From: Aradhya Bhatia <a-bhatia1@ti.com>

Add a helper API that can be used by the DSI hosts to find the required
input bus format for the given output dsi pixel format.

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Aradhya Bhatia <a-bhatia1@ti.com>
Signed-off-by: Aradhya Bhatia <aradhya.bhatia@linux.dev>
---
 drivers/gpu/drm/drm_mipi_dsi.c | 37 ++++++++++++++++++++++++++++++++++
 include/drm/drm_mipi_dsi.h     |  1 +
 2 files changed, 38 insertions(+)

diff --git a/drivers/gpu/drm/drm_mipi_dsi.c b/drivers/gpu/drm/drm_mipi_dsi.c
index 5e5c5f84daac..076826f2445a 100644
--- a/drivers/gpu/drm/drm_mipi_dsi.c
+++ b/drivers/gpu/drm/drm_mipi_dsi.c
@@ -36,6 +36,8 @@
 #include <drm/drm_mipi_dsi.h>
 #include <drm/drm_print.h>
 
+#include <linux/media-bus-format.h>
+
 #include <video/mipi_display.h>
 
 /**
@@ -870,6 +872,41 @@ ssize_t mipi_dsi_generic_read(struct mipi_dsi_device *dsi, const void *params,
 }
 EXPORT_SYMBOL(mipi_dsi_generic_read);
 
+/**
+ * drm_mipi_dsi_get_input_bus_fmt() - Get the required MEDIA_BUS_FMT_* based
+ *				      input pixel format for a given DSI output
+ *				      pixel format
+ * @dsi_format: pixel format that a DSI host needs to output
+ *
+ * Various DSI hosts can use this function during their
+ * &drm_bridge_funcs.atomic_get_input_bus_fmts operation to ascertain
+ * the MEDIA_BUS_FMT_* pixel format required as input.
+ *
+ * RETURNS:
+ * a 32-bit MEDIA_BUS_FMT_* value on success or 0 in case of failure.
+ */
+u32 drm_mipi_dsi_get_input_bus_fmt(enum mipi_dsi_pixel_format dsi_format)
+{
+	switch (dsi_format) {
+	case MIPI_DSI_FMT_RGB888:
+		return MEDIA_BUS_FMT_RGB888_1X24;
+
+	case MIPI_DSI_FMT_RGB666:
+		return MEDIA_BUS_FMT_RGB666_1X24_CPADHI;
+
+	case MIPI_DSI_FMT_RGB666_PACKED:
+		return MEDIA_BUS_FMT_RGB666_1X18;
+
+	case MIPI_DSI_FMT_RGB565:
+		return MEDIA_BUS_FMT_RGB565_1X16;
+
+	default:
+		/* Unsupported DSI Format */
+		return 0;
+	}
+}
+EXPORT_SYMBOL(drm_mipi_dsi_get_input_bus_fmt);
+
 /**
  * mipi_dsi_dcs_write_buffer() - transmit a DCS command with payload
  * @dsi: DSI peripheral device
diff --git a/include/drm/drm_mipi_dsi.h b/include/drm/drm_mipi_dsi.h
index 94400a78031f..9e2804e3a2b0 100644
--- a/include/drm/drm_mipi_dsi.h
+++ b/include/drm/drm_mipi_dsi.h
@@ -293,6 +293,7 @@ void mipi_dsi_generic_write_multi(struct mipi_dsi_multi_context *ctx,
 				  const void *payload, size_t size);
 ssize_t mipi_dsi_generic_read(struct mipi_dsi_device *dsi, const void *params,
 			      size_t num_params, void *data, size_t size);
+u32 drm_mipi_dsi_get_input_bus_fmt(enum mipi_dsi_pixel_format dsi_format);
 
 #define mipi_dsi_msleep(ctx, delay)	\
 	do {				\
-- 
2.34.1

From: Aradhya Bhatia <a-bhatia1@ti.com>

Change the existing (and deprecated) bridge hooks, to the bridge
atomic APIs.

Add drm helpers for duplicate_state, destroy_state, and bridge_reset
bridge hooks.

Further add support for the input format negotiation hook.

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Aradhya Bhatia <a-bhatia1@ti.com>
Signed-off-by: Aradhya Bhatia <aradhya.bhatia@linux.dev>
---
 .../gpu/drm/bridge/cadence/cdns-dsi-core.c    | 51 ++++++++++++++++---
 1 file changed, 43 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
index 284c468db6c3..7341e609dc8b 100644
--- a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
+++ b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
@@ -658,7 +658,8 @@ cdns_dsi_bridge_mode_valid(struct drm_bridge *bridge,
 	return MODE_OK;
 }
 
-static void cdns_dsi_bridge_disable(struct drm_bridge *bridge)
+static void cdns_dsi_bridge_atomic_disable(struct drm_bridge *bridge,
+					   struct drm_bridge_state *old_bridge_state)
 {
 	struct cdns_dsi_input *input = bridge_to_cdns_dsi_input(bridge);
 	struct cdns_dsi *dsi = input_to_dsi(input);
@@ -682,7 +683,8 @@ static void cdns_dsi_bridge_disable(struct drm_bridge *bridge)
 	pm_runtime_put(dsi->base.dev);
 }
 
-static void cdns_dsi_bridge_post_disable(struct drm_bridge *bridge)
+static void cdns_dsi_bridge_atomic_post_disable(struct drm_bridge *bridge,
+						struct drm_bridge_state *old_bridge_state)
 {
 	struct cdns_dsi_input *input = bridge_to_cdns_dsi_input(bridge);
 	struct cdns_dsi *dsi = input_to_dsi(input);
@@ -758,7 +760,8 @@ static void cdns_dsi_init_link(struct cdns_dsi *dsi)
 	dsi->link_initialized = true;
 }
 
-static void cdns_dsi_bridge_enable(struct drm_bridge *bridge)
+static void cdns_dsi_bridge_atomic_enable(struct drm_bridge *bridge,
+					  struct drm_bridge_state *old_bridge_state)
 {
 	struct cdns_dsi_input *input = bridge_to_cdns_dsi_input(bridge);
 	struct cdns_dsi *dsi = input_to_dsi(input);
@@ -911,7 +914,8 @@ static void cdns_dsi_bridge_enable(struct drm_bridge *bridge)
 	writel(tmp, dsi->regs + MCTL_MAIN_EN);
 }
 
-static void cdns_dsi_bridge_pre_enable(struct drm_bridge *bridge)
+static void cdns_dsi_bridge_atomic_pre_enable(struct drm_bridge *bridge,
+					      struct drm_bridge_state *old_bridge_state)
 {
 	struct cdns_dsi_input *input = bridge_to_cdns_dsi_input(bridge);
 	struct cdns_dsi *dsi = input_to_dsi(input);
@@ -923,13 +927,44 @@ static void cdns_dsi_bridge_pre_enable(struct drm_bridge *bridge)
 	cdns_dsi_hs_init(dsi);
 }
 
+static u32 *cdns_dsi_bridge_get_input_bus_fmts(struct drm_bridge *bridge,
+					       struct drm_bridge_state *bridge_state,
+					       struct drm_crtc_state *crtc_state,
+					       struct drm_connector_state *conn_state,
+					       u32 output_fmt,
+					       unsigned int *num_input_fmts)
+{
+	struct cdns_dsi_input *input = bridge_to_cdns_dsi_input(bridge);
+	struct cdns_dsi *dsi = input_to_dsi(input);
+	struct cdns_dsi_output *output = &dsi->output;
+	u32 *input_fmts;
+
+	*num_input_fmts = 0;
+
+	input_fmts = kzalloc(sizeof(*input_fmts), GFP_KERNEL);
+	if (!input_fmts)
+		return NULL;
+
+	input_fmts[0] = drm_mipi_dsi_get_input_bus_fmt(output->dev->format);
+	if (!input_fmts[0])
+		return NULL;
+
+	*num_input_fmts = 1;
+
+	return input_fmts;
+}
+
 static const struct drm_bridge_funcs cdns_dsi_bridge_funcs = {
 	.attach = cdns_dsi_bridge_attach,
 	.mode_valid = cdns_dsi_bridge_mode_valid,
-	.disable = cdns_dsi_bridge_disable,
-	.pre_enable = cdns_dsi_bridge_pre_enable,
-	.enable = cdns_dsi_bridge_enable,
-	.post_disable = cdns_dsi_bridge_post_disable,
+	.atomic_disable = cdns_dsi_bridge_atomic_disable,
+	.atomic_pre_enable = cdns_dsi_bridge_atomic_pre_enable,
+	.atomic_enable = cdns_dsi_bridge_atomic_enable,
+	.atomic_post_disable = cdns_dsi_bridge_atomic_post_disable,
+	.atomic_duplicate_state = drm_atomic_helper_bridge_duplicate_state,
+	.atomic_destroy_state = drm_atomic_helper_bridge_destroy_state,
+	.atomic_reset = drm_atomic_helper_bridge_reset,
+	.atomic_get_input_bus_fmts = cdns_dsi_bridge_get_input_bus_fmts,
 };
 
 static int cdns_dsi_attach(struct mipi_dsi_host *host,
-- 
2.34.1

From: Aradhya Bhatia <a-bhatia1@ti.com>

At present, the DSI mode configuration check happens during the
_atomic_enable() phase, which is not really the best place for this.
Moreover, if the mode is not valid, the driver gives a warning and
continues the hardware configuration.

Move the DSI mode configuration check to _atomic_check() instead, which
can properly report back any invalid mode, before the _enable phase even
begins.

Signed-off-by: Aradhya Bhatia <a-bhatia1@ti.com>
Signed-off-by: Aradhya Bhatia <aradhya.bhatia@linux.dev>
---
 drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c | 18 +++++++++++++++---
 drivers/gpu/drm/bridge/cadence/cdns-dsi-core.h |  1 +
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
index 7341e609dc8b..79d8c2264c14 100644
--- a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
+++ b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
@@ -769,7 +769,7 @@ static void cdns_dsi_bridge_atomic_enable(struct drm_bridge *bridge,
 	struct drm_display_mode *mode;
 	struct phy_configure_opts_mipi_dphy *phy_cfg = &output->phy_opts.mipi_dphy;
 	unsigned long tx_byte_period;
-	struct cdns_dsi_cfg dsi_cfg;
+	struct cdns_dsi_cfg dsi_cfg = dsi->dsi_cfg;
 	u32 tmp, reg_wakeup, div, status;
 	int nlanes;
 
@@ -782,8 +782,6 @@ static void cdns_dsi_bridge_atomic_enable(struct drm_bridge *bridge,
 	mode = &bridge->encoder->crtc->state->adjusted_mode;
 	nlanes = output->dev->lanes;
 
-	WARN_ON_ONCE(cdns_dsi_check_conf(dsi, mode, &dsi_cfg, false));
-
 	cdns_dsi_init_link(dsi);
 	cdns_dsi_hs_init(dsi);
 
@@ -954,6 +952,19 @@ static u32 *cdns_dsi_bridge_get_input_bus_fmts(struct drm_bridge *bridge,
 	return input_fmts;
 }
 
+static int cdns_dsi_bridge_atomic_check(struct drm_bridge *bridge,
+					struct drm_bridge_state *bridge_state,
+					struct drm_crtc_state *crtc_state,
+					struct drm_connector_state *conn_state)
+{
+	struct cdns_dsi_input *input = bridge_to_cdns_dsi_input(bridge);
+	struct cdns_dsi *dsi = input_to_dsi(input);
+	struct drm_display_mode *mode = &crtc_state->mode;
+	struct cdns_dsi_cfg *dsi_cfg = &dsi->dsi_cfg;
+
+	return cdns_dsi_check_conf(dsi, mode, dsi_cfg, false);
+}
+
 static const struct drm_bridge_funcs cdns_dsi_bridge_funcs = {
 	.attach = cdns_dsi_bridge_attach,
 	.mode_valid = cdns_dsi_bridge_mode_valid,
@@ -961,6 +972,7 @@ static const struct drm_bridge_funcs cdns_dsi_bridge_funcs = {
 	.atomic_pre_enable = cdns_dsi_bridge_atomic_pre_enable,
 	.atomic_enable = cdns_dsi_bridge_atomic_enable,
 	.atomic_post_disable = cdns_dsi_bridge_atomic_post_disable,
+	.atomic_check = cdns_dsi_bridge_atomic_check,
 	.atomic_duplicate_state = drm_atomic_helper_bridge_duplicate_state,
 	.atomic_destroy_state = drm_atomic_helper_bridge_destroy_state,
 	.atomic_reset = drm_atomic_helper_bridge_reset,
diff --git a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.h b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.h
index 5db5dbbbcaad..b785df45bc59 100644
--- a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.h
+++ b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.h
@@ -77,6 +77,7 @@ struct cdns_dsi {
 	bool link_initialized;
 	bool phy_initialized;
 	struct phy *dphy;
+	struct cdns_dsi_cfg dsi_cfg;
 };
 
 #endif /* !__CDNS_DSI_H__ */
-- 
2.34.1

On Sun, Oct 20, 2024 at 01:35:27AM +0530, Aradhya Bhatia wrote:
> From: Aradhya Bhatia <a-bhatia1@ti.com>
> 
> At present, the DSI mode configuration check happens during the
> _atomic_enable() phase, which is not really the best place for this.
> Moreover, if the mode is not valid, the driver gives a warning and
> continues the hardware configuration.
> 
> Move the DSI mode configuration check to _atomic_check() instead, which
> can properly report back any invalid mode, before the _enable phase even
> begins.
> 
> Signed-off-by: Aradhya Bhatia <a-bhatia1@ti.com>
> Signed-off-by: Aradhya Bhatia <aradhya.bhatia@linux.dev>
> ---
>  drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c | 18 +++++++++++++++---
>  drivers/gpu/drm/bridge/cadence/cdns-dsi-core.h |  1 +
>  2 files changed, 16 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
> index 7341e609dc8b..79d8c2264c14 100644
> --- a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
> +++ b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
> @@ -769,7 +769,7 @@ static void cdns_dsi_bridge_atomic_enable(struct drm_bridge *bridge,
>  	struct drm_display_mode *mode;
>  	struct phy_configure_opts_mipi_dphy *phy_cfg = &output->phy_opts.mipi_dphy;
>  	unsigned long tx_byte_period;
> -	struct cdns_dsi_cfg dsi_cfg;
> +	struct cdns_dsi_cfg dsi_cfg = dsi->dsi_cfg;
>  	u32 tmp, reg_wakeup, div, status;
>  	int nlanes;
>  
> @@ -782,8 +782,6 @@ static void cdns_dsi_bridge_atomic_enable(struct drm_bridge *bridge,
>  	mode = &bridge->encoder->crtc->state->adjusted_mode;
>  	nlanes = output->dev->lanes;
>  
> -	WARN_ON_ONCE(cdns_dsi_check_conf(dsi, mode, &dsi_cfg, false));
> -
>  	cdns_dsi_init_link(dsi);
>  	cdns_dsi_hs_init(dsi);
>  
> @@ -954,6 +952,19 @@ static u32 *cdns_dsi_bridge_get_input_bus_fmts(struct drm_bridge *bridge,
>  	return input_fmts;
>  }
>  
> +static int cdns_dsi_bridge_atomic_check(struct drm_bridge *bridge,
> +					struct drm_bridge_state *bridge_state,
> +					struct drm_crtc_state *crtc_state,
> +					struct drm_connector_state *conn_state)
> +{
> +	struct cdns_dsi_input *input = bridge_to_cdns_dsi_input(bridge);
> +	struct cdns_dsi *dsi = input_to_dsi(input);
> +	struct drm_display_mode *mode = &crtc_state->mode;
> +	struct cdns_dsi_cfg *dsi_cfg = &dsi->dsi_cfg;

This makes .atomic_check store data in the non-state structure. However
it is not guaranteed that each atomic_check() will result in the
atomic_commit(). So in addition to moving the check to the
atomic_check() callback you also have to move the cdns_dsi_cfg and all
other structures written during the check to the new structure, wrapping
drm_bridge_state.

> +
> +	return cdns_dsi_check_conf(dsi, mode, dsi_cfg, false);
> +}
> +
>  static const struct drm_bridge_funcs cdns_dsi_bridge_funcs = {
>  	.attach = cdns_dsi_bridge_attach,
>  	.mode_valid = cdns_dsi_bridge_mode_valid,
> @@ -961,6 +972,7 @@ static const struct drm_bridge_funcs cdns_dsi_bridge_funcs = {
>  	.atomic_pre_enable = cdns_dsi_bridge_atomic_pre_enable,
>  	.atomic_enable = cdns_dsi_bridge_atomic_enable,
>  	.atomic_post_disable = cdns_dsi_bridge_atomic_post_disable,
> +	.atomic_check = cdns_dsi_bridge_atomic_check,
>  	.atomic_duplicate_state = drm_atomic_helper_bridge_duplicate_state,
>  	.atomic_destroy_state = drm_atomic_helper_bridge_destroy_state,
>  	.atomic_reset = drm_atomic_helper_bridge_reset,
> diff --git a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.h b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.h
> index 5db5dbbbcaad..b785df45bc59 100644
> --- a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.h
> +++ b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.h
> @@ -77,6 +77,7 @@ struct cdns_dsi {
>  	bool link_initialized;
>  	bool phy_initialized;
>  	struct phy *dphy;
> +	struct cdns_dsi_cfg dsi_cfg;
>  };
>  
>  #endif /* !__CDNS_DSI_H__ */
> -- 
> 2.34.1
> 

-- 
With best wishes
Dmitry

From: Aradhya Bhatia <a-bhatia1@ti.com>

The way any singular display pipeline, in need of a modeset, gets
enabled is as follows -

	CRTC Enable
	All Bridge Pre-Enable
	Encoder Enable
	All Bridge Enable

- and the disable path is exactly the reverse of this.

The CRTC enable/disable occurs by looping over the old and new CRTC
states, while the bridge pre-enable, encoder enable, and bridge enable
occur by looping through the new connector states of the display
pipelines.

At the moment, the encoder and bridge operations are grouped together
and occur under the same loops.

Separate out the enable/disable loops of the encoder and bridge
operations into a different function, to make way for the re-ordering of
the enable and disable sequence of all these display elements.

This patch doesn't alter in any way the ordering of CRTC/encoder/bridge
enable and disable, but merely helps to cleanly set up for the next
patch and to make sure that the bisectibility remains intact.

Signed-off-by: Aradhya Bhatia <a-bhatia1@ti.com>
Signed-off-by: Aradhya Bhatia <aradhya.bhatia@linux.dev>
---
 drivers/gpu/drm/drm_atomic_helper.c | 97 +++++++++++++++++------------
 1 file changed, 57 insertions(+), 40 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index 5186d2114a50..7741fbcc8fc7 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -1122,11 +1122,10 @@ crtc_needs_disable(struct drm_crtc_state *old_state,
 }
 
 static void
-disable_outputs(struct drm_device *dev, struct drm_atomic_state *old_state)
+encoder_bridge_chain_disable(struct drm_device *dev, struct drm_atomic_state *old_state)
 {
 	struct drm_connector *connector;
 	struct drm_connector_state *old_conn_state, *new_conn_state;
-	struct drm_crtc *crtc;
 	struct drm_crtc_state *old_crtc_state, *new_crtc_state;
 	int i;
 
@@ -1189,6 +1188,16 @@ disable_outputs(struct drm_device *dev, struct drm_atomic_state *old_state)
 
 		drm_atomic_bridge_chain_post_disable(bridge, old_state);
 	}
+}
+
+static void
+disable_outputs(struct drm_device *dev, struct drm_atomic_state *old_state)
+{
+	struct drm_crtc *crtc;
+	struct drm_crtc_state *old_crtc_state, *new_crtc_state;
+	int i;
+
+	encoder_bridge_chain_disable(dev, old_state);
 
 	for_each_oldnew_crtc_in_state(old_state, crtc, old_crtc_state, new_crtc_state, i) {
 		const struct drm_crtc_helper_funcs *funcs;
@@ -1445,6 +1454,51 @@ static void drm_atomic_helper_commit_writebacks(struct drm_device *dev,
 	}
 }
 
+static void
+encoder_bridge_chain_enable(struct drm_device *dev, struct drm_atomic_state *old_state)
+{
+	struct drm_connector *connector;
+	struct drm_connector_state *new_conn_state;
+	int i;
+
+	for_each_new_connector_in_state(old_state, connector, new_conn_state, i) {
+		const struct drm_encoder_helper_funcs *funcs;
+		struct drm_encoder *encoder;
+		struct drm_bridge *bridge;
+
+		if (!new_conn_state->best_encoder)
+			continue;
+
+		if (!new_conn_state->crtc->state->active ||
+		    !drm_atomic_crtc_needs_modeset(new_conn_state->crtc->state))
+			continue;
+
+		encoder = new_conn_state->best_encoder;
+		funcs = encoder->helper_private;
+
+		drm_dbg_atomic(dev, "enabling [ENCODER:%d:%s]\n",
+			       encoder->base.id, encoder->name);
+
+		/*
+		 * Each encoder has at most one connector (since we always steal
+		 * it away), so we won't call enable hooks twice.
+		 */
+		bridge = drm_bridge_chain_get_first_bridge(encoder);
+		drm_atomic_bridge_chain_pre_enable(bridge, old_state);
+
+		if (funcs) {
+			if (funcs->atomic_enable)
+				funcs->atomic_enable(encoder, old_state);
+			else if (funcs->enable)
+				funcs->enable(encoder);
+			else if (funcs->commit)
+				funcs->commit(encoder);
+		}
+
+		drm_atomic_bridge_chain_enable(bridge, old_state);
+	}
+}
+
 /**
  * drm_atomic_helper_commit_modeset_enables - modeset commit to enable outputs
  * @dev: DRM device
@@ -1465,8 +1519,6 @@ void drm_atomic_helper_commit_modeset_enables(struct drm_device *dev,
 	struct drm_crtc *crtc;
 	struct drm_crtc_state *old_crtc_state;
 	struct drm_crtc_state *new_crtc_state;
-	struct drm_connector *connector;
-	struct drm_connector_state *new_conn_state;
 	int i;
 
 	for_each_oldnew_crtc_in_state(old_state, crtc, old_crtc_state, new_crtc_state, i) {
@@ -1491,42 +1543,7 @@ void drm_atomic_helper_commit_modeset_enables(struct drm_device *dev,
 		}
 	}
 
-	for_each_new_connector_in_state(old_state, connector, new_conn_state, i) {
-		const struct drm_encoder_helper_funcs *funcs;
-		struct drm_encoder *encoder;
-		struct drm_bridge *bridge;
-
-		if (!new_conn_state->best_encoder)
-			continue;
-
-		if (!new_conn_state->crtc->state->active ||
-		    !drm_atomic_crtc_needs_modeset(new_conn_state->crtc->state))
-			continue;
-
-		encoder = new_conn_state->best_encoder;
-		funcs = encoder->helper_private;
-
-		drm_dbg_atomic(dev, "enabling [ENCODER:%d:%s]\n",
-			       encoder->base.id, encoder->name);
-
-		/*
-		 * Each encoder has at most one connector (since we always steal
-		 * it away), so we won't call enable hooks twice.
-		 */
-		bridge = drm_bridge_chain_get_first_bridge(encoder);
-		drm_atomic_bridge_chain_pre_enable(bridge, old_state);
-
-		if (funcs) {
-			if (funcs->atomic_enable)
-				funcs->atomic_enable(encoder, old_state);
-			else if (funcs->enable)
-				funcs->enable(encoder);
-			else if (funcs->commit)
-				funcs->commit(encoder);
-		}
-
-		drm_atomic_bridge_chain_enable(bridge, old_state);
-	}
+	encoder_bridge_chain_enable(dev, old_state);
 
 	drm_atomic_helper_commit_writebacks(dev, old_state);
 }
-- 
2.34.1

On Sun, Oct 20, 2024 at 01:35:28AM +0530, Aradhya Bhatia wrote:
> From: Aradhya Bhatia <a-bhatia1@ti.com>
> 
> The way any singular display pipeline, in need of a modeset, gets
> enabled is as follows -
> 
> 	CRTC Enable
> 	All Bridge Pre-Enable
> 	Encoder Enable
> 	All Bridge Enable
> 
> - and the disable path is exactly the reverse of this.
> 
> The CRTC enable/disable occurs by looping over the old and new CRTC
> states, while the bridge pre-enable, encoder enable, and bridge enable
> occur by looping through the new connector states of the display
> pipelines.
> 
> At the moment, the encoder and bridge operations are grouped together
> and occur under the same loops.
> 
> Separate out the enable/disable loops of the encoder and bridge
> operations into a different function, to make way for the re-ordering of
> the enable and disable sequence of all these display elements.
> 
> This patch doesn't alter in any way the ordering of CRTC/encoder/bridge
> enable and disable, but merely helps to cleanly set up for the next
> patch and to make sure that the bisectibility remains intact.
> 
> Signed-off-by: Aradhya Bhatia <a-bhatia1@ti.com>
> Signed-off-by: Aradhya Bhatia <aradhya.bhatia@linux.dev>
> ---
>  drivers/gpu/drm/drm_atomic_helper.c | 97 +++++++++++++++++------------
>  1 file changed, 57 insertions(+), 40 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 5186d2114a50..7741fbcc8fc7 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -1122,11 +1122,10 @@ crtc_needs_disable(struct drm_crtc_state *old_state,
>  }
>  
>  static void
> -disable_outputs(struct drm_device *dev, struct drm_atomic_state *old_state)
> +encoder_bridge_chain_disable(struct drm_device *dev, struct drm_atomic_state *old_state)
>  {
>  	struct drm_connector *connector;
>  	struct drm_connector_state *old_conn_state, *new_conn_state;
> -	struct drm_crtc *crtc;
>  	struct drm_crtc_state *old_crtc_state, *new_crtc_state;
>  	int i;
>  
> @@ -1189,6 +1188,16 @@ disable_outputs(struct drm_device *dev, struct drm_atomic_state *old_state)
>  
>  		drm_atomic_bridge_chain_post_disable(bridge, old_state);
>  	}
> +}
> +
> +static void
> +disable_outputs(struct drm_device *dev, struct drm_atomic_state *old_state)
> +{
> +	struct drm_crtc *crtc;
> +	struct drm_crtc_state *old_crtc_state, *new_crtc_state;
> +	int i;
> +
> +	encoder_bridge_chain_disable(dev, old_state);
>  
>  	for_each_oldnew_crtc_in_state(old_state, crtc, old_crtc_state, new_crtc_state, i) {
>  		const struct drm_crtc_helper_funcs *funcs;
> @@ -1445,6 +1454,51 @@ static void drm_atomic_helper_commit_writebacks(struct drm_device *dev,
>  	}
>  }
>  
> +static void
> +encoder_bridge_chain_enable(struct drm_device *dev, struct drm_atomic_state *old_state)
> +{
> +	struct drm_connector *connector;
> +	struct drm_connector_state *new_conn_state;
> +	int i;
> +
> +	for_each_new_connector_in_state(old_state, connector, new_conn_state, i) {
> +		const struct drm_encoder_helper_funcs *funcs;
> +		struct drm_encoder *encoder;
> +		struct drm_bridge *bridge;
> +
> +		if (!new_conn_state->best_encoder)
> +			continue;
> +
> +		if (!new_conn_state->crtc->state->active ||
> +		    !drm_atomic_crtc_needs_modeset(new_conn_state->crtc->state))
> +			continue;
> +
> +		encoder = new_conn_state->best_encoder;
> +		funcs = encoder->helper_private;
> +
> +		drm_dbg_atomic(dev, "enabling [ENCODER:%d:%s]\n",
> +			       encoder->base.id, encoder->name);
> +
> +		/*
> +		 * Each encoder has at most one connector (since we always steal
> +		 * it away), so we won't call enable hooks twice.
> +		 */
> +		bridge = drm_bridge_chain_get_first_bridge(encoder);
> +		drm_atomic_bridge_chain_pre_enable(bridge, old_state);
> +
> +		if (funcs) {
> +			if (funcs->atomic_enable)
> +				funcs->atomic_enable(encoder, old_state);
> +			else if (funcs->enable)
> +				funcs->enable(encoder);
> +			else if (funcs->commit)
> +				funcs->commit(encoder);
> +		}
> +
> +		drm_atomic_bridge_chain_enable(bridge, old_state);
> +	}
> +}
> +
>  /**
>   * drm_atomic_helper_commit_modeset_enables - modeset commit to enable outputs
>   * @dev: DRM device
> @@ -1465,8 +1519,6 @@ void drm_atomic_helper_commit_modeset_enables(struct drm_device *dev,
>  	struct drm_crtc *crtc;
>  	struct drm_crtc_state *old_crtc_state;
>  	struct drm_crtc_state *new_crtc_state;
> -	struct drm_connector *connector;
> -	struct drm_connector_state *new_conn_state;
>  	int i;
>  
>  	for_each_oldnew_crtc_in_state(old_state, crtc, old_crtc_state, new_crtc_state, i) {
> @@ -1491,42 +1543,7 @@ void drm_atomic_helper_commit_modeset_enables(struct drm_device *dev,
>  		}
>  	}

I'd say, if you want for it to be cleaner, split both loops from
drm_atomic_helper_commit_modeset_enables() and call them separately.
This save you from the code move, which is harder to review (and also
helps with the function complexity).

>  
> -	for_each_new_connector_in_state(old_state, connector, new_conn_state, i) {
> -		const struct drm_encoder_helper_funcs *funcs;
> -		struct drm_encoder *encoder;
> -		struct drm_bridge *bridge;
> -
> -		if (!new_conn_state->best_encoder)
> -			continue;
> -
> -		if (!new_conn_state->crtc->state->active ||
> -		    !drm_atomic_crtc_needs_modeset(new_conn_state->crtc->state))
> -			continue;
> -
> -		encoder = new_conn_state->best_encoder;
> -		funcs = encoder->helper_private;
> -
> -		drm_dbg_atomic(dev, "enabling [ENCODER:%d:%s]\n",
> -			       encoder->base.id, encoder->name);
> -
> -		/*
> -		 * Each encoder has at most one connector (since we always steal
> -		 * it away), so we won't call enable hooks twice.
> -		 */
> -		bridge = drm_bridge_chain_get_first_bridge(encoder);
> -		drm_atomic_bridge_chain_pre_enable(bridge, old_state);
> -
> -		if (funcs) {
> -			if (funcs->atomic_enable)
> -				funcs->atomic_enable(encoder, old_state);
> -			else if (funcs->enable)
> -				funcs->enable(encoder);
> -			else if (funcs->commit)
> -				funcs->commit(encoder);
> -		}
> -
> -		drm_atomic_bridge_chain_enable(bridge, old_state);
> -	}
> +	encoder_bridge_chain_enable(dev, old_state);
>  
>  	drm_atomic_helper_commit_writebacks(dev, old_state);
>  }
> -- 
> 2.34.1
> 

-- 
With best wishes
Dmitry

From: Aradhya Bhatia <a-bhatia1@ti.com>

Move the bridge pre_enable call before crtc enable, and the bridge
post_disable call after the crtc disable.

The sequence of enable after this patch will look like:

	bridge[n]_pre_enable
	...
	bridge[1]_pre_enable

	crtc_enable
	encoder_enable

	bridge[1]_enable
	...
	bridge[n]_enable

and vice-versa for the bridge chain disable sequence.

The definition of bridge pre_enable hook says that,
"The display pipe (i.e. clocks and timing signals) feeding this bridge
will not yet be running when this callback is called".

Since CRTC is also a source feeding the bridge, it should not be enabled
before the bridges in the pipeline are pre_enabled. Fix that by
re-ordering the sequence of bridge pre_enable and bridge post_disable.

Signed-off-by: Aradhya Bhatia <a-bhatia1@ti.com>
Signed-off-by: Aradhya Bhatia <aradhya.bhatia@linux.dev>
---
 drivers/gpu/drm/drm_atomic_helper.c | 102 ++++++++++++++++++----------
 include/drm/drm_atomic_helper.h     |   5 ++
 2 files changed, 71 insertions(+), 36 deletions(-)

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index 7741fbcc8fc7..6ebd869df79b 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -1122,7 +1122,8 @@ crtc_needs_disable(struct drm_crtc_state *old_state,
 }
 
 static void
-encoder_bridge_chain_disable(struct drm_device *dev, struct drm_atomic_state *old_state)
+encoder_bridge_chain_disable(struct drm_device *dev, struct drm_atomic_state *old_state,
+			     enum bridge_chain_operation_type op_type)
 {
 	struct drm_connector *connector;
 	struct drm_connector_state *old_conn_state, *new_conn_state;
@@ -1162,31 +1163,43 @@ encoder_bridge_chain_disable(struct drm_device *dev, struct drm_atomic_state *ol
 		if (WARN_ON(!encoder))
 			continue;
 
-		funcs = encoder->helper_private;
-
-		drm_dbg_atomic(dev, "disabling [ENCODER:%d:%s]\n",
-			       encoder->base.id, encoder->name);
-
 		/*
 		 * Each encoder has at most one connector (since we always steal
 		 * it away), so we won't call disable hooks twice.
 		 */
 		bridge = drm_bridge_chain_get_first_bridge(encoder);
-		drm_atomic_bridge_chain_disable(bridge, old_state);
 
-		/* Right function depends upon target state. */
-		if (funcs) {
-			if (funcs->atomic_disable)
-				funcs->atomic_disable(encoder, old_state);
-			else if (new_conn_state->crtc && funcs->prepare)
-				funcs->prepare(encoder);
-			else if (funcs->disable)
-				funcs->disable(encoder);
-			else if (funcs->dpms)
-				funcs->dpms(encoder, DRM_MODE_DPMS_OFF);
-		}
+		switch (op_type) {
+		case DRM_BRIDGE_ENABLE_DISABLE:
+			funcs = encoder->helper_private;
+
+			drm_dbg_atomic(dev, "disabling [ENCODER:%d:%s]\n",
+				       encoder->base.id, encoder->name);
+
+			drm_atomic_bridge_chain_disable(bridge, old_state);
+
+			/* Right function depends upon target state. */
+			if (funcs) {
+				if (funcs->atomic_disable)
+					funcs->atomic_disable(encoder, old_state);
+				else if (new_conn_state->crtc && funcs->prepare)
+					funcs->prepare(encoder);
+				else if (funcs->disable)
+					funcs->disable(encoder);
+				else if (funcs->dpms)
+					funcs->dpms(encoder, DRM_MODE_DPMS_OFF);
+			}
 
-		drm_atomic_bridge_chain_post_disable(bridge, old_state);
+			break;
+
+		case DRM_BRIDGE_PRE_ENABLE_POST_DISABLE:
+			drm_atomic_bridge_chain_post_disable(bridge, old_state);
+			break;
+
+		default:
+			drm_err(dev, "Unrecognized Encoder/Bridge Operation (%d).\n", op_type);
+			break;
+		}
 	}
 }
 
@@ -1197,7 +1210,7 @@ disable_outputs(struct drm_device *dev, struct drm_atomic_state *old_state)
 	struct drm_crtc_state *old_crtc_state, *new_crtc_state;
 	int i;
 
-	encoder_bridge_chain_disable(dev, old_state);
+	encoder_bridge_chain_disable(dev, old_state, DRM_BRIDGE_ENABLE_DISABLE);
 
 	for_each_oldnew_crtc_in_state(old_state, crtc, old_crtc_state, new_crtc_state, i) {
 		const struct drm_crtc_helper_funcs *funcs;
@@ -1243,6 +1256,8 @@ disable_outputs(struct drm_device *dev, struct drm_atomic_state *old_state)
 		if (ret == 0)
 			drm_crtc_vblank_put(crtc);
 	}
+
+	encoder_bridge_chain_disable(dev, old_state, DRM_BRIDGE_PRE_ENABLE_POST_DISABLE);
 }
 
 /**
@@ -1455,7 +1470,8 @@ static void drm_atomic_helper_commit_writebacks(struct drm_device *dev,
 }
 
 static void
-encoder_bridge_chain_enable(struct drm_device *dev, struct drm_atomic_state *old_state)
+encoder_bridge_chain_enable(struct drm_device *dev, struct drm_atomic_state *old_state,
+			    enum bridge_chain_operation_type op_type)
 {
 	struct drm_connector *connector;
 	struct drm_connector_state *new_conn_state;
@@ -1474,28 +1490,40 @@ encoder_bridge_chain_enable(struct drm_device *dev, struct drm_atomic_state *old
 			continue;
 
 		encoder = new_conn_state->best_encoder;
-		funcs = encoder->helper_private;
-
-		drm_dbg_atomic(dev, "enabling [ENCODER:%d:%s]\n",
-			       encoder->base.id, encoder->name);
 
 		/*
 		 * Each encoder has at most one connector (since we always steal
 		 * it away), so we won't call enable hooks twice.
 		 */
 		bridge = drm_bridge_chain_get_first_bridge(encoder);
-		drm_atomic_bridge_chain_pre_enable(bridge, old_state);
 
-		if (funcs) {
-			if (funcs->atomic_enable)
-				funcs->atomic_enable(encoder, old_state);
-			else if (funcs->enable)
-				funcs->enable(encoder);
-			else if (funcs->commit)
-				funcs->commit(encoder);
-		}
+		switch (op_type) {
+		case DRM_BRIDGE_PRE_ENABLE_POST_DISABLE:
+			drm_atomic_bridge_chain_pre_enable(bridge, old_state);
+			break;
+
+		case DRM_BRIDGE_ENABLE_DISABLE:
+			funcs = encoder->helper_private;
+
+			drm_dbg_atomic(dev, "enabling [ENCODER:%d:%s]\n",
+				       encoder->base.id, encoder->name);
 
-		drm_atomic_bridge_chain_enable(bridge, old_state);
+			if (funcs) {
+				if (funcs->atomic_enable)
+					funcs->atomic_enable(encoder, old_state);
+				else if (funcs->enable)
+					funcs->enable(encoder);
+				else if (funcs->commit)
+					funcs->commit(encoder);
+			}
+
+			drm_atomic_bridge_chain_enable(bridge, old_state);
+			break;
+
+		default:
+			drm_err(dev, "Unrecognized Encoder/Bridge Operation (%d).\n", op_type);
+			break;
+		}
 	}
 }
 
@@ -1521,6 +1549,8 @@ void drm_atomic_helper_commit_modeset_enables(struct drm_device *dev,
 	struct drm_crtc_state *new_crtc_state;
 	int i;
 
+	encoder_bridge_chain_enable(dev, old_state, DRM_BRIDGE_PRE_ENABLE_POST_DISABLE);
+
 	for_each_oldnew_crtc_in_state(old_state, crtc, old_crtc_state, new_crtc_state, i) {
 		const struct drm_crtc_helper_funcs *funcs;
 
@@ -1543,7 +1573,7 @@ void drm_atomic_helper_commit_modeset_enables(struct drm_device *dev,
 		}
 	}
 
-	encoder_bridge_chain_enable(dev, old_state);
+	encoder_bridge_chain_enable(dev, old_state, DRM_BRIDGE_ENABLE_DISABLE);
 
 	drm_atomic_helper_commit_writebacks(dev, old_state);
 }
diff --git a/include/drm/drm_atomic_helper.h b/include/drm/drm_atomic_helper.h
index 9aa0a05aa072..92a5812adc6c 100644
--- a/include/drm/drm_atomic_helper.h
+++ b/include/drm/drm_atomic_helper.h
@@ -43,6 +43,11 @@
  */
 #define DRM_PLANE_NO_SCALING (1<<16)
 
+enum bridge_chain_operation_type {
+	DRM_BRIDGE_PRE_ENABLE_POST_DISABLE,
+	DRM_BRIDGE_ENABLE_DISABLE,
+};
+
 struct drm_atomic_state;
 struct drm_private_obj;
 struct drm_private_state;
-- 
2.34.1

On Sun, Oct 20, 2024 at 01:35:29AM +0530, Aradhya Bhatia wrote:
> From: Aradhya Bhatia <a-bhatia1@ti.com>
> 
> Move the bridge pre_enable call before crtc enable, and the bridge
> post_disable call after the crtc disable.
> 
> The sequence of enable after this patch will look like:
> 
> 	bridge[n]_pre_enable
> 	...
> 	bridge[1]_pre_enable
> 
> 	crtc_enable
> 	encoder_enable
> 
> 	bridge[1]_enable
> 	...
> 	bridge[n]_enable
> 
> and vice-versa for the bridge chain disable sequence.
> 
> The definition of bridge pre_enable hook says that,
> "The display pipe (i.e. clocks and timing signals) feeding this bridge
> will not yet be running when this callback is called".
> 
> Since CRTC is also a source feeding the bridge, it should not be enabled
> before the bridges in the pipeline are pre_enabled. Fix that by
> re-ordering the sequence of bridge pre_enable and bridge post_disable.
> 
> Signed-off-by: Aradhya Bhatia <a-bhatia1@ti.com>
> Signed-off-by: Aradhya Bhatia <aradhya.bhatia@linux.dev>
> ---
>  drivers/gpu/drm/drm_atomic_helper.c | 102 ++++++++++++++++++----------
>  include/drm/drm_atomic_helper.h     |   5 ++
>  2 files changed, 71 insertions(+), 36 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 7741fbcc8fc7..6ebd869df79b 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -1122,7 +1122,8 @@ crtc_needs_disable(struct drm_crtc_state *old_state,
>  }
>  
>  static void
> -encoder_bridge_chain_disable(struct drm_device *dev, struct drm_atomic_state *old_state)
> +encoder_bridge_chain_disable(struct drm_device *dev, struct drm_atomic_state *old_state,
> +			     enum bridge_chain_operation_type op_type)
>  {
>  	struct drm_connector *connector;
>  	struct drm_connector_state *old_conn_state, *new_conn_state;
> @@ -1162,31 +1163,43 @@ encoder_bridge_chain_disable(struct drm_device *dev, struct drm_atomic_state *ol
>  		if (WARN_ON(!encoder))
>  			continue;
>  
> -		funcs = encoder->helper_private;
> -
> -		drm_dbg_atomic(dev, "disabling [ENCODER:%d:%s]\n",
> -			       encoder->base.id, encoder->name);
> -
>  		/*
>  		 * Each encoder has at most one connector (since we always steal
>  		 * it away), so we won't call disable hooks twice.
>  		 */
>  		bridge = drm_bridge_chain_get_first_bridge(encoder);
> -		drm_atomic_bridge_chain_disable(bridge, old_state);
>  
> -		/* Right function depends upon target state. */
> -		if (funcs) {
> -			if (funcs->atomic_disable)
> -				funcs->atomic_disable(encoder, old_state);
> -			else if (new_conn_state->crtc && funcs->prepare)
> -				funcs->prepare(encoder);
> -			else if (funcs->disable)
> -				funcs->disable(encoder);
> -			else if (funcs->dpms)
> -				funcs->dpms(encoder, DRM_MODE_DPMS_OFF);
> -		}
> +		switch (op_type) {
> +		case DRM_BRIDGE_ENABLE_DISABLE:
> +			funcs = encoder->helper_private;
> +
> +			drm_dbg_atomic(dev, "disabling [ENCODER:%d:%s]\n",
> +				       encoder->base.id, encoder->name);
> +
> +			drm_atomic_bridge_chain_disable(bridge, old_state);
> +
> +			/* Right function depends upon target state. */
> +			if (funcs) {
> +				if (funcs->atomic_disable)
> +					funcs->atomic_disable(encoder, old_state);
> +				else if (new_conn_state->crtc && funcs->prepare)
> +					funcs->prepare(encoder);
> +				else if (funcs->disable)
> +					funcs->disable(encoder);
> +				else if (funcs->dpms)
> +					funcs->dpms(encoder, DRM_MODE_DPMS_OFF);
> +			}
>  
> -		drm_atomic_bridge_chain_post_disable(bridge, old_state);
> +			break;
> +
> +		case DRM_BRIDGE_PRE_ENABLE_POST_DISABLE:
> +			drm_atomic_bridge_chain_post_disable(bridge, old_state);
> +			break;
> +
> +		default:
> +			drm_err(dev, "Unrecognized Encoder/Bridge Operation (%d).\n", op_type);
> +			break;
> +		}
>  	}
>  }
>  
> @@ -1197,7 +1210,7 @@ disable_outputs(struct drm_device *dev, struct drm_atomic_state *old_state)
>  	struct drm_crtc_state *old_crtc_state, *new_crtc_state;
>  	int i;
>  
> -	encoder_bridge_chain_disable(dev, old_state);
> +	encoder_bridge_chain_disable(dev, old_state, DRM_BRIDGE_ENABLE_DISABLE);
>  
>  	for_each_oldnew_crtc_in_state(old_state, crtc, old_crtc_state, new_crtc_state, i) {
>  		const struct drm_crtc_helper_funcs *funcs;
> @@ -1243,6 +1256,8 @@ disable_outputs(struct drm_device *dev, struct drm_atomic_state *old_state)
>  		if (ret == 0)
>  			drm_crtc_vblank_put(crtc);
>  	}
> +
> +	encoder_bridge_chain_disable(dev, old_state, DRM_BRIDGE_PRE_ENABLE_POST_DISABLE);
>  }
>  
>  /**
> @@ -1455,7 +1470,8 @@ static void drm_atomic_helper_commit_writebacks(struct drm_device *dev,
>  }
>  
>  static void
> -encoder_bridge_chain_enable(struct drm_device *dev, struct drm_atomic_state *old_state)
> +encoder_bridge_chain_enable(struct drm_device *dev, struct drm_atomic_state *old_state,
> +			    enum bridge_chain_operation_type op_type)
>  {
>  	struct drm_connector *connector;
>  	struct drm_connector_state *new_conn_state;
> @@ -1474,28 +1490,40 @@ encoder_bridge_chain_enable(struct drm_device *dev, struct drm_atomic_state *old
>  			continue;
>  
>  		encoder = new_conn_state->best_encoder;
> -		funcs = encoder->helper_private;
> -
> -		drm_dbg_atomic(dev, "enabling [ENCODER:%d:%s]\n",
> -			       encoder->base.id, encoder->name);
>  
>  		/*
>  		 * Each encoder has at most one connector (since we always steal
>  		 * it away), so we won't call enable hooks twice.
>  		 */
>  		bridge = drm_bridge_chain_get_first_bridge(encoder);
> -		drm_atomic_bridge_chain_pre_enable(bridge, old_state);
>  
> -		if (funcs) {
> -			if (funcs->atomic_enable)
> -				funcs->atomic_enable(encoder, old_state);
> -			else if (funcs->enable)
> -				funcs->enable(encoder);
> -			else if (funcs->commit)
> -				funcs->commit(encoder);
> -		}
> +		switch (op_type) {
> +		case DRM_BRIDGE_PRE_ENABLE_POST_DISABLE:
> +			drm_atomic_bridge_chain_pre_enable(bridge, old_state);
> +			break;
> +
> +		case DRM_BRIDGE_ENABLE_DISABLE:
> +			funcs = encoder->helper_private;
> +
> +			drm_dbg_atomic(dev, "enabling [ENCODER:%d:%s]\n",
> +				       encoder->base.id, encoder->name);
>  
> -		drm_atomic_bridge_chain_enable(bridge, old_state);
> +			if (funcs) {
> +				if (funcs->atomic_enable)
> +					funcs->atomic_enable(encoder, old_state);
> +				else if (funcs->enable)
> +					funcs->enable(encoder);
> +				else if (funcs->commit)
> +					funcs->commit(encoder);
> +			}
> +
> +			drm_atomic_bridge_chain_enable(bridge, old_state);
> +			break;
> +
> +		default:
> +			drm_err(dev, "Unrecognized Encoder/Bridge Operation (%d).\n", op_type);
> +			break;
> +		}
>  	}
>  }
>  
> @@ -1521,6 +1549,8 @@ void drm_atomic_helper_commit_modeset_enables(struct drm_device *dev,
>  	struct drm_crtc_state *new_crtc_state;
>  	int i;
>  
> +	encoder_bridge_chain_enable(dev, old_state, DRM_BRIDGE_PRE_ENABLE_POST_DISABLE);
> +
>  	for_each_oldnew_crtc_in_state(old_state, crtc, old_crtc_state, new_crtc_state, i) {
>  		const struct drm_crtc_helper_funcs *funcs;
>  
> @@ -1543,7 +1573,7 @@ void drm_atomic_helper_commit_modeset_enables(struct drm_device *dev,
>  		}
>  	}
>  
> -	encoder_bridge_chain_enable(dev, old_state);
> +	encoder_bridge_chain_enable(dev, old_state, DRM_BRIDGE_ENABLE_DISABLE);
>  
>  	drm_atomic_helper_commit_writebacks(dev, old_state);
>  }
> diff --git a/include/drm/drm_atomic_helper.h b/include/drm/drm_atomic_helper.h
> index 9aa0a05aa072..92a5812adc6c 100644
> --- a/include/drm/drm_atomic_helper.h
> +++ b/include/drm/drm_atomic_helper.h
> @@ -43,6 +43,11 @@
>   */
>  #define DRM_PLANE_NO_SCALING (1<<16)
>  
> +enum bridge_chain_operation_type {
> +	DRM_BRIDGE_PRE_ENABLE_POST_DISABLE,
> +	DRM_BRIDGE_ENABLE_DISABLE,
> +};
> +

The enum doesn't need to be public, does it?

>  struct drm_atomic_state;
>  struct drm_private_obj;
>  struct drm_private_state;
> -- 
> 2.34.1
> 

-- 
With best wishes
Dmitry

From: Aradhya Bhatia <a-bhatia1@ti.com>

The cdns-dsi controller requires that it be turned on completely before
the input DPI's source has begun streaming[0]. Not having that, allows
for a small window before cdns-dsi enable and after cdns-dsi disable
where the previous entity (in this case tidss's videoport) to continue
streaming DPI video signals. This small window where cdns-dsi is
disabled but is still receiving signals causes the input FIFO of
cdns-dsi to get corrupted. This causes the colors to shift on the output
display. The colors can either shift by one color component (R->G, G->B,
B->R), or by two color components (R->B, G->R, B->G).

Since tidss's videoport starts streaming via crtc enable hooks, we need
cdns-dsi to be up and running before that. Now that the bridges are
pre_enabled before crtc is enabled, and post_disabled after crtc is
disabled, use the pre_enable and post_disable hooks to get cdns-dsi
ready and running before the tidss videoport to get pass the color shift
issues.

[0]: See section 12.6.5.7.3 "Start-up Procedure" in J721E SoC TRM
     TRM Link: http://www.ti.com/lit/pdf/spruil1

Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Aradhya Bhatia <a-bhatia1@ti.com>
Signed-off-by: Aradhya Bhatia <aradhya.bhatia@linux.dev>
---
 .../gpu/drm/bridge/cadence/cdns-dsi-core.c    | 62 ++++++++++---------
 1 file changed, 34 insertions(+), 28 deletions(-)

diff --git a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
index 79d8c2264c14..dfeb53841ebc 100644
--- a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
+++ b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
@@ -658,13 +658,28 @@ cdns_dsi_bridge_mode_valid(struct drm_bridge *bridge,
 	return MODE_OK;
 }
 
-static void cdns_dsi_bridge_atomic_disable(struct drm_bridge *bridge,
-					   struct drm_bridge_state *old_bridge_state)
+static void cdns_dsi_bridge_atomic_post_disable(struct drm_bridge *bridge,
+						struct drm_bridge_state *old_bridge_state)
 {
 	struct cdns_dsi_input *input = bridge_to_cdns_dsi_input(bridge);
 	struct cdns_dsi *dsi = input_to_dsi(input);
 	u32 val;
 
+	/*
+	 * The cdns-dsi controller needs to be disabled after it's DPI source
+	 * has stopped streaming. If this is not followed, there is a brief
+	 * window before DPI source is disabled and after cdns-dsi controller
+	 * has been disabled where the DPI stream is still on, but the cdns-dsi
+	 * controller is not ready anymore to accept the incoming signals. This
+	 * is one of the reasons why a shift in pixel colors is observed on
+	 * displays that have cdns-dsi as one of the bridges.
+	 *
+	 * To mitigate this, disable this bridge from the bridge post_disable()
+	 * hook, instead of the bridge _disable() hook. The bridge post_disable()
+	 * hook gets called after the CRTC disable, where often many DPI sources
+	 * disable their streams.
+	 */
+
 	val = readl(dsi->regs + MCTL_MAIN_DATA_CTL);
 	val &= ~(IF_VID_SELECT_MASK | IF_VID_MODE | VID_EN | HOST_EOT_GEN |
 		 DISP_EOT_GEN);
@@ -683,15 +698,6 @@ static void cdns_dsi_bridge_atomic_disable(struct drm_bridge *bridge,
 	pm_runtime_put(dsi->base.dev);
 }
 
-static void cdns_dsi_bridge_atomic_post_disable(struct drm_bridge *bridge,
-						struct drm_bridge_state *old_bridge_state)
-{
-	struct cdns_dsi_input *input = bridge_to_cdns_dsi_input(bridge);
-	struct cdns_dsi *dsi = input_to_dsi(input);
-
-	pm_runtime_put(dsi->base.dev);
-}
-
 static void cdns_dsi_hs_init(struct cdns_dsi *dsi)
 {
 	struct cdns_dsi_output *output = &dsi->output;
@@ -760,8 +766,8 @@ static void cdns_dsi_init_link(struct cdns_dsi *dsi)
 	dsi->link_initialized = true;
 }
 
-static void cdns_dsi_bridge_atomic_enable(struct drm_bridge *bridge,
-					  struct drm_bridge_state *old_bridge_state)
+static void cdns_dsi_bridge_atomic_pre_enable(struct drm_bridge *bridge,
+					      struct drm_bridge_state *old_bridge_state)
 {
 	struct cdns_dsi_input *input = bridge_to_cdns_dsi_input(bridge);
 	struct cdns_dsi *dsi = input_to_dsi(input);
@@ -776,6 +782,21 @@ static void cdns_dsi_bridge_atomic_enable(struct drm_bridge *bridge,
 	if (WARN_ON(pm_runtime_get_sync(dsi->base.dev) < 0))
 		return;
 
+	/*
+	 * The cdns-dsi controller needs to be enabled before it's DPI source
+	 * has begun streaming. If this is not followed, there is a brief window
+	 * after DPI source enable and before cdns-dsi controller enable where
+	 * the DPI stream is on, but the cdns-dsi controller is not ready to
+	 * accept the incoming signals. This is one of the reasons why a shift
+	 * in pixel colors is observed on displays that have cdns-dsi as one of
+	 * the bridges.
+	 *
+	 * To mitigate this, enable this bridge from the bridge pre_enable()
+	 * hook, instead of the bridge _enable() hook. The bridge pre_enable()
+	 * hook gets called before the CRTC enable, where often many DPI sources
+	 * enable their streams.
+	 */
+
 	if (dsi->platform_ops && dsi->platform_ops->enable)
 		dsi->platform_ops->enable(dsi);
 
@@ -912,19 +933,6 @@ static void cdns_dsi_bridge_atomic_enable(struct drm_bridge *bridge,
 	writel(tmp, dsi->regs + MCTL_MAIN_EN);
 }
 
-static void cdns_dsi_bridge_atomic_pre_enable(struct drm_bridge *bridge,
-					      struct drm_bridge_state *old_bridge_state)
-{
-	struct cdns_dsi_input *input = bridge_to_cdns_dsi_input(bridge);
-	struct cdns_dsi *dsi = input_to_dsi(input);
-
-	if (WARN_ON(pm_runtime_get_sync(dsi->base.dev) < 0))
-		return;
-
-	cdns_dsi_init_link(dsi);
-	cdns_dsi_hs_init(dsi);
-}
-
 static u32 *cdns_dsi_bridge_get_input_bus_fmts(struct drm_bridge *bridge,
 					       struct drm_bridge_state *bridge_state,
 					       struct drm_crtc_state *crtc_state,
@@ -968,9 +976,7 @@ static int cdns_dsi_bridge_atomic_check(struct drm_bridge *bridge,
 static const struct drm_bridge_funcs cdns_dsi_bridge_funcs = {
 	.attach = cdns_dsi_bridge_attach,
 	.mode_valid = cdns_dsi_bridge_mode_valid,
-	.atomic_disable = cdns_dsi_bridge_atomic_disable,
 	.atomic_pre_enable = cdns_dsi_bridge_atomic_pre_enable,
-	.atomic_enable = cdns_dsi_bridge_atomic_enable,
 	.atomic_post_disable = cdns_dsi_bridge_atomic_post_disable,
 	.atomic_check = cdns_dsi_bridge_atomic_check,
 	.atomic_duplicate_state = drm_atomic_helper_bridge_duplicate_state,
-- 
2.34.1

On Sun, Oct 20, 2024 at 01:35:30AM +0530, Aradhya Bhatia wrote:
> From: Aradhya Bhatia <a-bhatia1@ti.com>
> 
> The cdns-dsi controller requires that it be turned on completely before
> the input DPI's source has begun streaming[0]. Not having that, allows
> for a small window before cdns-dsi enable and after cdns-dsi disable
> where the previous entity (in this case tidss's videoport) to continue
> streaming DPI video signals. This small window where cdns-dsi is
> disabled but is still receiving signals causes the input FIFO of
> cdns-dsi to get corrupted. This causes the colors to shift on the output
> display. The colors can either shift by one color component (R->G, G->B,
> B->R), or by two color components (R->B, G->R, B->G).
> 
> Since tidss's videoport starts streaming via crtc enable hooks, we need
> cdns-dsi to be up and running before that. Now that the bridges are
> pre_enabled before crtc is enabled, and post_disabled after crtc is
> disabled, use the pre_enable and post_disable hooks to get cdns-dsi
> ready and running before the tidss videoport to get pass the color shift
> issues.
> 

Not being an expert in the TI DSS driver, would it be more proper to
handle that in the TI driver instead? I mean, sending out DPI signals
isn't a part of the CRTC setup, it's a job of the encoder.

> [0]: See section 12.6.5.7.3 "Start-up Procedure" in J721E SoC TRM
>      TRM Link: http://www.ti.com/lit/pdf/spruil1
> 
> Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
> Signed-off-by: Aradhya Bhatia <a-bhatia1@ti.com>
> Signed-off-by: Aradhya Bhatia <aradhya.bhatia@linux.dev>
> ---
>  .../gpu/drm/bridge/cadence/cdns-dsi-core.c    | 62 ++++++++++---------
>  1 file changed, 34 insertions(+), 28 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
> index 79d8c2264c14..dfeb53841ebc 100644
> --- a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
> +++ b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
> @@ -658,13 +658,28 @@ cdns_dsi_bridge_mode_valid(struct drm_bridge *bridge,
>  	return MODE_OK;
>  }
>  
> -static void cdns_dsi_bridge_atomic_disable(struct drm_bridge *bridge,
> -					   struct drm_bridge_state *old_bridge_state)
> +static void cdns_dsi_bridge_atomic_post_disable(struct drm_bridge *bridge,
> +						struct drm_bridge_state *old_bridge_state)
>  {
>  	struct cdns_dsi_input *input = bridge_to_cdns_dsi_input(bridge);
>  	struct cdns_dsi *dsi = input_to_dsi(input);
>  	u32 val;
>  
> +	/*
> +	 * The cdns-dsi controller needs to be disabled after it's DPI source
> +	 * has stopped streaming. If this is not followed, there is a brief
> +	 * window before DPI source is disabled and after cdns-dsi controller
> +	 * has been disabled where the DPI stream is still on, but the cdns-dsi
> +	 * controller is not ready anymore to accept the incoming signals. This
> +	 * is one of the reasons why a shift in pixel colors is observed on
> +	 * displays that have cdns-dsi as one of the bridges.
> +	 *
> +	 * To mitigate this, disable this bridge from the bridge post_disable()
> +	 * hook, instead of the bridge _disable() hook. The bridge post_disable()
> +	 * hook gets called after the CRTC disable, where often many DPI sources
> +	 * disable their streams.
> +	 */
> +
>  	val = readl(dsi->regs + MCTL_MAIN_DATA_CTL);
>  	val &= ~(IF_VID_SELECT_MASK | IF_VID_MODE | VID_EN | HOST_EOT_GEN |
>  		 DISP_EOT_GEN);
> @@ -683,15 +698,6 @@ static void cdns_dsi_bridge_atomic_disable(struct drm_bridge *bridge,
>  	pm_runtime_put(dsi->base.dev);
>  }
>  
> -static void cdns_dsi_bridge_atomic_post_disable(struct drm_bridge *bridge,
> -						struct drm_bridge_state *old_bridge_state)
> -{
> -	struct cdns_dsi_input *input = bridge_to_cdns_dsi_input(bridge);
> -	struct cdns_dsi *dsi = input_to_dsi(input);
> -
> -	pm_runtime_put(dsi->base.dev);
> -}
> -
>  static void cdns_dsi_hs_init(struct cdns_dsi *dsi)
>  {
>  	struct cdns_dsi_output *output = &dsi->output;
> @@ -760,8 +766,8 @@ static void cdns_dsi_init_link(struct cdns_dsi *dsi)
>  	dsi->link_initialized = true;
>  }
>  
> -static void cdns_dsi_bridge_atomic_enable(struct drm_bridge *bridge,
> -					  struct drm_bridge_state *old_bridge_state)
> +static void cdns_dsi_bridge_atomic_pre_enable(struct drm_bridge *bridge,
> +					      struct drm_bridge_state *old_bridge_state)
>  {
>  	struct cdns_dsi_input *input = bridge_to_cdns_dsi_input(bridge);
>  	struct cdns_dsi *dsi = input_to_dsi(input);
> @@ -776,6 +782,21 @@ static void cdns_dsi_bridge_atomic_enable(struct drm_bridge *bridge,
>  	if (WARN_ON(pm_runtime_get_sync(dsi->base.dev) < 0))
>  		return;
>  
> +	/*
> +	 * The cdns-dsi controller needs to be enabled before it's DPI source
> +	 * has begun streaming. If this is not followed, there is a brief window
> +	 * after DPI source enable and before cdns-dsi controller enable where
> +	 * the DPI stream is on, but the cdns-dsi controller is not ready to
> +	 * accept the incoming signals. This is one of the reasons why a shift
> +	 * in pixel colors is observed on displays that have cdns-dsi as one of
> +	 * the bridges.
> +	 *
> +	 * To mitigate this, enable this bridge from the bridge pre_enable()
> +	 * hook, instead of the bridge _enable() hook. The bridge pre_enable()
> +	 * hook gets called before the CRTC enable, where often many DPI sources
> +	 * enable their streams.
> +	 */
> +
>  	if (dsi->platform_ops && dsi->platform_ops->enable)
>  		dsi->platform_ops->enable(dsi);
>  
> @@ -912,19 +933,6 @@ static void cdns_dsi_bridge_atomic_enable(struct drm_bridge *bridge,
>  	writel(tmp, dsi->regs + MCTL_MAIN_EN);
>  }
>  
> -static void cdns_dsi_bridge_atomic_pre_enable(struct drm_bridge *bridge,
> -					      struct drm_bridge_state *old_bridge_state)
> -{
> -	struct cdns_dsi_input *input = bridge_to_cdns_dsi_input(bridge);
> -	struct cdns_dsi *dsi = input_to_dsi(input);
> -
> -	if (WARN_ON(pm_runtime_get_sync(dsi->base.dev) < 0))
> -		return;
> -
> -	cdns_dsi_init_link(dsi);
> -	cdns_dsi_hs_init(dsi);
> -}
> -
>  static u32 *cdns_dsi_bridge_get_input_bus_fmts(struct drm_bridge *bridge,
>  					       struct drm_bridge_state *bridge_state,
>  					       struct drm_crtc_state *crtc_state,
> @@ -968,9 +976,7 @@ static int cdns_dsi_bridge_atomic_check(struct drm_bridge *bridge,
>  static const struct drm_bridge_funcs cdns_dsi_bridge_funcs = {
>  	.attach = cdns_dsi_bridge_attach,
>  	.mode_valid = cdns_dsi_bridge_mode_valid,
> -	.atomic_disable = cdns_dsi_bridge_atomic_disable,
>  	.atomic_pre_enable = cdns_dsi_bridge_atomic_pre_enable,
> -	.atomic_enable = cdns_dsi_bridge_atomic_enable,
>  	.atomic_post_disable = cdns_dsi_bridge_atomic_post_disable,
>  	.atomic_check = cdns_dsi_bridge_atomic_check,
>  	.atomic_duplicate_state = drm_atomic_helper_bridge_duplicate_state,
> -- 
> 2.34.1
> 

-- 
With best wishes
Dmitry

Hi Dmitry,

Thank you for reviewing the patches!

On 10/20/24 17:27, Dmitry Baryshkov wrote:
> On Sun, Oct 20, 2024 at 01:35:30AM +0530, Aradhya Bhatia wrote:
>> From: Aradhya Bhatia <a-bhatia1@ti.com>
>>
>> The cdns-dsi controller requires that it be turned on completely before
>> the input DPI's source has begun streaming[0]. Not having that, allows
>> for a small window before cdns-dsi enable and after cdns-dsi disable
>> where the previous entity (in this case tidss's videoport) to continue
>> streaming DPI video signals. This small window where cdns-dsi is
>> disabled but is still receiving signals causes the input FIFO of
>> cdns-dsi to get corrupted. This causes the colors to shift on the output
>> display. The colors can either shift by one color component (R->G, G->B,
>> B->R), or by two color components (R->B, G->R, B->G).
>>
>> Since tidss's videoport starts streaming via crtc enable hooks, we need
>> cdns-dsi to be up and running before that. Now that the bridges are
>> pre_enabled before crtc is enabled, and post_disabled after crtc is
>> disabled, use the pre_enable and post_disable hooks to get cdns-dsi
>> ready and running before the tidss videoport to get pass the color shift
>> issues.
>>
> 
> Not being an expert in the TI DSS driver, would it be more proper to
> handle that in the TI driver instead? I mean, sending out DPI signals
> isn't a part of the CRTC setup, it's a job of the encoder.

I haven't done a feasibility analysis of moving the CRTC bits of TIDSS
into the encoder, but even if it were possible, it wouldn't solve the
issue.

The bridge_enable() sequence gets called _after_ the encoder has been
enabled - causing the TIDSS's DPI (enabled from encoder) to still be
up and running before the DSI has had a chance to be ready.

Regards
Aradhya


> 
>> [0]: See section 12.6.5.7.3 "Start-up Procedure" in J721E SoC TRM
>>      TRM Link: http://www.ti.com/lit/pdf/spruil1
>>
>> Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
>> Signed-off-by: Aradhya Bhatia <a-bhatia1@ti.com>
>> Signed-off-by: Aradhya Bhatia <aradhya.bhatia@linux.dev>
>> ---
>>  .../gpu/drm/bridge/cadence/cdns-dsi-core.c    | 62 ++++++++++---------
>>  1 file changed, 34 insertions(+), 28 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
>> index 79d8c2264c14..dfeb53841ebc 100644
>> --- a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
>> +++ b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
>> @@ -658,13 +658,28 @@ cdns_dsi_bridge_mode_valid(struct drm_bridge *bridge,
>>  	return MODE_OK;
>>  }
>>  
>> -static void cdns_dsi_bridge_atomic_disable(struct drm_bridge *bridge,
>> -					   struct drm_bridge_state *old_bridge_state)
>> +static void cdns_dsi_bridge_atomic_post_disable(struct drm_bridge *bridge,
>> +						struct drm_bridge_state *old_bridge_state)
>>  {
>>  	struct cdns_dsi_input *input = bridge_to_cdns_dsi_input(bridge);
>>  	struct cdns_dsi *dsi = input_to_dsi(input);
>>  	u32 val;
>>  
>> +	/*
>> +	 * The cdns-dsi controller needs to be disabled after it's DPI source
>> +	 * has stopped streaming. If this is not followed, there is a brief
>> +	 * window before DPI source is disabled and after cdns-dsi controller
>> +	 * has been disabled where the DPI stream is still on, but the cdns-dsi
>> +	 * controller is not ready anymore to accept the incoming signals. This
>> +	 * is one of the reasons why a shift in pixel colors is observed on
>> +	 * displays that have cdns-dsi as one of the bridges.
>> +	 *
>> +	 * To mitigate this, disable this bridge from the bridge post_disable()
>> +	 * hook, instead of the bridge _disable() hook. The bridge post_disable()
>> +	 * hook gets called after the CRTC disable, where often many DPI sources
>> +	 * disable their streams.
>> +	 */
>> +
>>  	val = readl(dsi->regs + MCTL_MAIN_DATA_CTL);
>>  	val &= ~(IF_VID_SELECT_MASK | IF_VID_MODE | VID_EN | HOST_EOT_GEN |
>>  		 DISP_EOT_GEN);
>> @@ -683,15 +698,6 @@ static void cdns_dsi_bridge_atomic_disable(struct drm_bridge *bridge,
>>  	pm_runtime_put(dsi->base.dev);
>>  }
>>  
>> -static void cdns_dsi_bridge_atomic_post_disable(struct drm_bridge *bridge,
>> -						struct drm_bridge_state *old_bridge_state)
>> -{
>> -	struct cdns_dsi_input *input = bridge_to_cdns_dsi_input(bridge);
>> -	struct cdns_dsi *dsi = input_to_dsi(input);
>> -
>> -	pm_runtime_put(dsi->base.dev);
>> -}
>> -
>>  static void cdns_dsi_hs_init(struct cdns_dsi *dsi)
>>  {
>>  	struct cdns_dsi_output *output = &dsi->output;
>> @@ -760,8 +766,8 @@ static void cdns_dsi_init_link(struct cdns_dsi *dsi)
>>  	dsi->link_initialized = true;
>>  }
>>  
>> -static void cdns_dsi_bridge_atomic_enable(struct drm_bridge *bridge,
>> -					  struct drm_bridge_state *old_bridge_state)
>> +static void cdns_dsi_bridge_atomic_pre_enable(struct drm_bridge *bridge,
>> +					      struct drm_bridge_state *old_bridge_state)
>>  {
>>  	struct cdns_dsi_input *input = bridge_to_cdns_dsi_input(bridge);
>>  	struct cdns_dsi *dsi = input_to_dsi(input);
>> @@ -776,6 +782,21 @@ static void cdns_dsi_bridge_atomic_enable(struct drm_bridge *bridge,
>>  	if (WARN_ON(pm_runtime_get_sync(dsi->base.dev) < 0))
>>  		return;
>>  
>> +	/*
>> +	 * The cdns-dsi controller needs to be enabled before it's DPI source
>> +	 * has begun streaming. If this is not followed, there is a brief window
>> +	 * after DPI source enable and before cdns-dsi controller enable where
>> +	 * the DPI stream is on, but the cdns-dsi controller is not ready to
>> +	 * accept the incoming signals. This is one of the reasons why a shift
>> +	 * in pixel colors is observed on displays that have cdns-dsi as one of
>> +	 * the bridges.
>> +	 *
>> +	 * To mitigate this, enable this bridge from the bridge pre_enable()
>> +	 * hook, instead of the bridge _enable() hook. The bridge pre_enable()
>> +	 * hook gets called before the CRTC enable, where often many DPI sources
>> +	 * enable their streams.
>> +	 */
>> +
>>  	if (dsi->platform_ops && dsi->platform_ops->enable)
>>  		dsi->platform_ops->enable(dsi);
>>  
>> @@ -912,19 +933,6 @@ static void cdns_dsi_bridge_atomic_enable(struct drm_bridge *bridge,
>>  	writel(tmp, dsi->regs + MCTL_MAIN_EN);
>>  }
>>  
>> -static void cdns_dsi_bridge_atomic_pre_enable(struct drm_bridge *bridge,
>> -					      struct drm_bridge_state *old_bridge_state)
>> -{
>> -	struct cdns_dsi_input *input = bridge_to_cdns_dsi_input(bridge);
>> -	struct cdns_dsi *dsi = input_to_dsi(input);
>> -
>> -	if (WARN_ON(pm_runtime_get_sync(dsi->base.dev) < 0))
>> -		return;
>> -
>> -	cdns_dsi_init_link(dsi);
>> -	cdns_dsi_hs_init(dsi);
>> -}
>> -
>>  static u32 *cdns_dsi_bridge_get_input_bus_fmts(struct drm_bridge *bridge,
>>  					       struct drm_bridge_state *bridge_state,
>>  					       struct drm_crtc_state *crtc_state,
>> @@ -968,9 +976,7 @@ static int cdns_dsi_bridge_atomic_check(struct drm_bridge *bridge,
>>  static const struct drm_bridge_funcs cdns_dsi_bridge_funcs = {
>>  	.attach = cdns_dsi_bridge_attach,
>>  	.mode_valid = cdns_dsi_bridge_mode_valid,
>> -	.atomic_disable = cdns_dsi_bridge_atomic_disable,
>>  	.atomic_pre_enable = cdns_dsi_bridge_atomic_pre_enable,
>> -	.atomic_enable = cdns_dsi_bridge_atomic_enable,
>>  	.atomic_post_disable = cdns_dsi_bridge_atomic_post_disable,
>>  	.atomic_check = cdns_dsi_bridge_atomic_check,
>>  	.atomic_duplicate_state = drm_atomic_helper_bridge_duplicate_state,
>> -- 
>> 2.34.1
>>
>

On Mon, 21 Oct 2024 at 20:07, Aradhya Bhatia <aradhya.bhatia@linux.dev> wrote:
>
> Hi Dmitry,
>
> Thank you for reviewing the patches!
>
> On 10/20/24 17:27, Dmitry Baryshkov wrote:
> > On Sun, Oct 20, 2024 at 01:35:30AM +0530, Aradhya Bhatia wrote:
> >> From: Aradhya Bhatia <a-bhatia1@ti.com>
> >>
> >> The cdns-dsi controller requires that it be turned on completely before
> >> the input DPI's source has begun streaming[0]. Not having that, allows
> >> for a small window before cdns-dsi enable and after cdns-dsi disable
> >> where the previous entity (in this case tidss's videoport) to continue
> >> streaming DPI video signals. This small window where cdns-dsi is
> >> disabled but is still receiving signals causes the input FIFO of
> >> cdns-dsi to get corrupted. This causes the colors to shift on the output
> >> display. The colors can either shift by one color component (R->G, G->B,
> >> B->R), or by two color components (R->B, G->R, B->G).
> >>
> >> Since tidss's videoport starts streaming via crtc enable hooks, we need
> >> cdns-dsi to be up and running before that. Now that the bridges are
> >> pre_enabled before crtc is enabled, and post_disabled after crtc is
> >> disabled, use the pre_enable and post_disable hooks to get cdns-dsi
> >> ready and running before the tidss videoport to get pass the color shift
> >> issues.
> >>
> >
> > Not being an expert in the TI DSS driver, would it be more proper to
> > handle that in the TI driver instead? I mean, sending out DPI signals
> > isn't a part of the CRTC setup, it's a job of the encoder.
>
> I haven't done a feasibility analysis of moving the CRTC bits of TIDSS
> into the encoder, but even if it were possible, it wouldn't solve the
> issue.
>
> The bridge_enable() sequence gets called _after_ the encoder has been
> enabled - causing the TIDSS's DPI (enabled from encoder) to still be
> up and running before the DSI has had a chance to be ready.

But then you can move CDSI setup to pre_enable, so that all setup
happens before encoder's (= DPI) being enabled.


-- 
With best wishes
Dmitry

On 10/22/24 00:09, Dmitry Baryshkov wrote:
> On Mon, 21 Oct 2024 at 20:07, Aradhya Bhatia <aradhya.bhatia@linux.dev> wrote:
>>
>> Hi Dmitry,
>>
>> Thank you for reviewing the patches!
>>
>> On 10/20/24 17:27, Dmitry Baryshkov wrote:
>>> On Sun, Oct 20, 2024 at 01:35:30AM +0530, Aradhya Bhatia wrote:
>>>> From: Aradhya Bhatia <a-bhatia1@ti.com>
>>>>
>>>> The cdns-dsi controller requires that it be turned on completely before
>>>> the input DPI's source has begun streaming[0]. Not having that, allows
>>>> for a small window before cdns-dsi enable and after cdns-dsi disable
>>>> where the previous entity (in this case tidss's videoport) to continue
>>>> streaming DPI video signals. This small window where cdns-dsi is
>>>> disabled but is still receiving signals causes the input FIFO of
>>>> cdns-dsi to get corrupted. This causes the colors to shift on the output
>>>> display. The colors can either shift by one color component (R->G, G->B,
>>>> B->R), or by two color components (R->B, G->R, B->G).
>>>>
>>>> Since tidss's videoport starts streaming via crtc enable hooks, we need
>>>> cdns-dsi to be up and running before that. Now that the bridges are
>>>> pre_enabled before crtc is enabled, and post_disabled after crtc is
>>>> disabled, use the pre_enable and post_disable hooks to get cdns-dsi
>>>> ready and running before the tidss videoport to get pass the color shift
>>>> issues.
>>>>
>>>
>>> Not being an expert in the TI DSS driver, would it be more proper to
>>> handle that in the TI driver instead? I mean, sending out DPI signals
>>> isn't a part of the CRTC setup, it's a job of the encoder.
>>
>> I haven't done a feasibility analysis of moving the CRTC bits of TIDSS
>> into the encoder, but even if it were possible, it wouldn't solve the
>> issue.
>>
>> The bridge_enable() sequence gets called _after_ the encoder has been
>> enabled - causing the TIDSS's DPI (enabled from encoder) to still be
>> up and running before the DSI has had a chance to be ready.
> 
> But then you can move CDSI setup to pre_enable, so that all setup
> happens before encoder's (= DPI) being enabled.
> 
> 

Ah! I did not realize that you were suggesting against moving
_bridge_pre_enable() to before crtc_enable().

I think, despite its initial complexity, it is a good idea to move the
_bridge_pre_enable() before the crtc_enable().

The boundary between an encoder and a CRTC in the modern display
hardware seems to have blurred a bit. Maybe the tidss / cdns-dsi is a
unique case (only for now), but of course, tidss is not
the only one generating the DPI signal from the CRTC.

And bridges should be allowed an option to get _some_ configuration done
before the CRTC and encoder are up and running, and I think that's where
the re-ordering is of the essence.

My initial version did suggest creating a new API[0], "_early_enable()"
that allowed _pre_enable() to remain where it is, all the while allowing
the bridges to have the option of configuring before the signals start
getting generated in the pipeline. That idea was then translated into
the current one.


Regards
Aradhya


[0]: https://lore.kernel.org/all/20240511153051.1355825-7-a-bhatia1@ti.com/