The LT9611 has two DSI input ports. The driver currently assumes Port A
is always used for single-port configurations. However, some boards
connect DSI to Port B only.

Update the driver to detect which ports are populated from devicetree
and configure the hardware accordingly:

- If only port@1 (Port B) is populated, configure port swap (0x8303
  bit 6) and byte_clk source (0x8250 bit 3:2) for Port B operation
- If both ports are populated, use dual-port mode (Port A + B)
- If only port@0 (Port A) is populated, use single Port A (existing
  behavior)

Signed-off-by: Hongyang Zhao <hongyang.zhao@thundersoft.com>
Reviewed-by: Roger Shimizu <rosh@debian.org>
---
 drivers/gpu/drm/bridge/lontium-lt9611.c | 46 +++++++++++++++++++++++----------
 1 file changed, 32 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/bridge/lontium-lt9611.c b/drivers/gpu/drm/bridge/lontium-lt9611.c
index a2d032ee4744..5fc22489b078 100644
--- a/drivers/gpu/drm/bridge/lontium-lt9611.c
+++ b/drivers/gpu/drm/bridge/lontium-lt9611.c
@@ -116,12 +116,25 @@ static int lt9611_mipi_input_digital(struct lt9611 *lt9611,
 		{ 0x830a, 0x00 },
 		{ 0x824f, 0x80 },
 		{ 0x8250, 0x10 },
+		{ 0x8303, 0x00 },
 		{ 0x8302, 0x0a },
 		{ 0x8306, 0x0a },
 	};
 
-	if (lt9611->dsi1_node)
-		reg_cfg[1].def = 0x03;
+	if (lt9611->dsi1_node) {
+		if (lt9611->dsi0_node) {
+			/* Dual port (Port A + B) */
+			reg_cfg[1].def = 0x03;
+		} else {
+			/*
+			 * Single port B:
+			 * - 0x8303 bit 6: port swap (1=PortB as primary)
+			 * - 0x8250 bit 3:2: byte_clk source (01=PortB)
+			 */
+			reg_cfg[3].def = 0x14;
+			reg_cfg[4].def = 0x40;
+		}
+	}
 
 	return regmap_multi_reg_write(lt9611->regmap, reg_cfg, ARRAY_SIZE(reg_cfg));
 }
@@ -202,7 +215,9 @@ static void lt9611_pcr_setup(struct lt9611 *lt9611, const struct drm_display_mod
 	regmap_write(lt9611->regmap, 0x831d, pol);
 
 	regmap_multi_reg_write(lt9611->regmap, reg_cfg, ARRAY_SIZE(reg_cfg));
-	if (lt9611->dsi1_node) {
+
+	/* dual port: configure hact for combining two DSI inputs */
+	if (lt9611->dsi0_node && lt9611->dsi1_node) {
 		unsigned int hact = mode->hdisplay;
 
 		hact >>= 2;
@@ -759,7 +774,8 @@ static enum drm_mode_status lt9611_bridge_mode_valid(struct drm_bridge *bridge,
 	if (mode->hdisplay > 3840)
 		return MODE_BAD_HVALUE;
 
-	if (mode->hdisplay > 2000 && !lt9611->dsi1_node)
+	/* high resolution requires dual port (Port A + B) */
+	if (mode->hdisplay > 2000 && !(lt9611->dsi0_node && lt9611->dsi1_node))
 		return MODE_PANEL;
 
 	return MODE_OK;
@@ -1015,13 +1031,13 @@ static int lt9611_parse_dt(struct device *dev,
 			   struct lt9611 *lt9611)
 {
 	lt9611->dsi0_node = of_graph_get_remote_node(dev->of_node, 0, -1);
-	if (!lt9611->dsi0_node) {
-		dev_err(lt9611->dev, "failed to get remote node for primary dsi\n");
+	lt9611->dsi1_node = of_graph_get_remote_node(dev->of_node, 1, -1);
+
+	if (!lt9611->dsi0_node && !lt9611->dsi1_node) {
+		dev_err(lt9611->dev, "failed to get remote node for dsi\n");
 		return -ENODEV;
 	}
 
-	lt9611->dsi1_node = of_graph_get_remote_node(dev->of_node, 1, -1);
-
 	lt9611->ac_mode = of_property_read_bool(dev->of_node, "lt,ac-mode");
 
 	return drm_of_find_panel_or_bridge(dev->of_node, 2, -1, NULL, &lt9611->next_bridge);
@@ -1142,14 +1158,16 @@ static int lt9611_probe(struct i2c_client *client)
 
 	drm_bridge_add(&lt9611->bridge);
 
-	/* Attach primary DSI */
-	lt9611->dsi0 = lt9611_attach_dsi(lt9611, lt9611->dsi0_node);
-	if (IS_ERR(lt9611->dsi0)) {
-		ret = PTR_ERR(lt9611->dsi0);
-		goto err_remove_bridge;
+	/* Attach primary DSI (directly drives or Port A in dual-port mode) */
+	if (lt9611->dsi0_node) {
+		lt9611->dsi0 = lt9611_attach_dsi(lt9611, lt9611->dsi0_node);
+		if (IS_ERR(lt9611->dsi0)) {
+			ret = PTR_ERR(lt9611->dsi0);
+			goto err_remove_bridge;
+		}
 	}
 
-	/* Attach secondary DSI, if specified */
+	/* Attach secondary DSI (Port B in single or dual-port mode) */
 	if (lt9611->dsi1_node) {
 		lt9611->dsi1 = lt9611_attach_dsi(lt9611, lt9611->dsi1_node);
 		if (IS_ERR(lt9611->dsi1)) {

-- 
2.43.0

On Wed, Jan 28, 2026 at 07:15:46PM +0800, Hongyang Zhao wrote:
> The LT9611 has two DSI input ports. The driver currently assumes Port A
> is always used for single-port configurations. However, some boards
> connect DSI to Port B only.
> 
> Update the driver to detect which ports are populated from devicetree
> and configure the hardware accordingly:
> 
> - If only port@1 (Port B) is populated, configure port swap (0x8303
>   bit 6) and byte_clk source (0x8250 bit 3:2) for Port B operation
> - If both ports are populated, use dual-port mode (Port A + B)
> - If only port@0 (Port A) is populated, use single Port A (existing
>   behavior)
> 
> Signed-off-by: Hongyang Zhao <hongyang.zhao@thundersoft.com>
> Reviewed-by: Roger Shimizu <rosh@debian.org>
> ---
>  drivers/gpu/drm/bridge/lontium-lt9611.c | 46 +++++++++++++++++++++++----------
>  1 file changed, 32 insertions(+), 14 deletions(-)
> 

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>


-- 
With best wishes
Dmitry