Create mipi_dsi_dcs_read_multi(), which accepts a mipi_dsi_multi_context
struct for improved error handling and cleaner panel driver code.

Create mipi_dsi_dcs_write_var_seq_multi() and
mipi_dsi_generic_write_var_seq_multi() macros which allow MIPI panel
drivers to write non-static data to display controllers.

Signed-off-by: Brigham Campbell <me@brighamcampbell.com>
---

I looked into using __builtin_constant_p() to extend
mipi_dsi_{generic,dcs}_write_seq_multi() to accept both static and
non-static sequences of bytes and store them accordingly, it looked
promising at first, but I found no such solution ultimately. At the very
least, if we find a solution at some point, my hope is that cocinelle
could be used to replace each of the new var_seq_multi() usages among
drivers with an improved seq_multi().


 drivers/gpu/drm/drm_mipi_dsi.c | 37 ++++++++++++++++++++++++++++++++++
 include/drm/drm_mipi_dsi.h     | 35 ++++++++++++++++++++++++++++++++
 2 files changed, 72 insertions(+)

diff --git a/drivers/gpu/drm/drm_mipi_dsi.c b/drivers/gpu/drm/drm_mipi_dsi.c
index a00d76443128..0f2c3be98212 100644
--- a/drivers/gpu/drm/drm_mipi_dsi.c
+++ b/drivers/gpu/drm/drm_mipi_dsi.c
@@ -1075,6 +1075,43 @@ ssize_t mipi_dsi_dcs_read(struct mipi_dsi_device *dsi, u8 cmd, void *data,
 }
 EXPORT_SYMBOL(mipi_dsi_dcs_read);
 
+/**
+ * mipi_dsi_dcs_read_multi() - mipi_dsi_dcs_read() w/ accum_err
+ * @ctx: Context for multiple DSI transactions
+ * @cmd: DCS command
+ * @data: buffer in which to receive data
+ * @len: size of receive buffer
+ *
+ * Like mipi_dsi_dcs_read() but deals with errors in a way that makes it
+ * convenient to make several calls in a row.
+ */
+void mipi_dsi_dcs_read_multi(struct mipi_dsi_multi_context *ctx, u8 cmd,
+			     void *data, size_t len)
+{
+	struct mipi_dsi_device *dsi = ctx->dsi;
+	struct device *dev = &dsi->dev;
+	struct mipi_dsi_msg msg = {
+		.channel = dsi->channel,
+		.type = MIPI_DSI_DCS_READ,
+		.tx_buf = &cmd,
+		.tx_len = 1,
+		.rx_buf = data,
+		.rx_len = len
+	};
+	ssize_t ret;
+
+	if (ctx->accum_err)
+		return;
+
+	ret = mipi_dsi_device_transfer(dsi, &msg);
+	if (ret < 0) {
+		ctx->accum_err = ret;
+		dev_err(dev, "dcs read with command %#x failed: %d\n", cmd,
+			ctx->accum_err);
+	}
+}
+EXPORT_SYMBOL(mipi_dsi_dcs_read_multi);
+
 /**
  * mipi_dsi_dcs_nop() - send DCS nop packet
  * @dsi: DSI peripheral device
diff --git a/include/drm/drm_mipi_dsi.h b/include/drm/drm_mipi_dsi.h
index 369b0d8830c3..bfee4071e89e 100644
--- a/include/drm/drm_mipi_dsi.h
+++ b/include/drm/drm_mipi_dsi.h
@@ -333,6 +333,8 @@ ssize_t mipi_dsi_dcs_write(struct mipi_dsi_device *dsi, u8 cmd,
 			   const void *data, size_t len);
 ssize_t mipi_dsi_dcs_read(struct mipi_dsi_device *dsi, u8 cmd, void *data,
 			  size_t len);
+void mipi_dsi_dcs_read_multi(struct mipi_dsi_multi_context *ctx, u8 cmd,
+			     void *data, size_t len);
 int mipi_dsi_dcs_nop(struct mipi_dsi_device *dsi);
 int mipi_dsi_dcs_soft_reset(struct mipi_dsi_device *dsi);
 int mipi_dsi_dcs_get_power_mode(struct mipi_dsi_device *dsi, u8 *mode);
@@ -415,6 +417,22 @@ void mipi_dsi_dcs_set_tear_off_multi(struct mipi_dsi_multi_context *ctx);
 		mipi_dsi_generic_write_multi(ctx, d, ARRAY_SIZE(d)); \
 	} while (0)
 
+/**
+ * mipi_dsi_generic_write_var_seq_multi - transmit non-static data using a
+ * generic write packet
+ *
+ * This macro will print errors for you and error handling is optimized for
+ * callers that call this multiple times in a row.
+ *
+ * @ctx: Context for multiple DSI transactions
+ * @seq: buffer containing the payload
+ */
+#define mipi_dsi_generic_write_var_seq_multi(ctx, seq...)	     \
+	do {							     \
+		const u8 d[] = { seq };				     \
+		mipi_dsi_generic_write_multi(ctx, d, ARRAY_SIZE(d)); \
+	} while (0)
+
 /**
  * mipi_dsi_dcs_write_seq_multi - transmit a DCS command with payload
  *
@@ -431,6 +449,23 @@ void mipi_dsi_dcs_set_tear_off_multi(struct mipi_dsi_multi_context *ctx);
 		mipi_dsi_dcs_write_buffer_multi(ctx, d, ARRAY_SIZE(d)); \
 	} while (0)
 
+/**
+ * mipi_dsi_dcs_write_var_seq_multi - transmit a DCS command with non-static
+ * payload
+ *
+ * This macro will print errors for you and error handling is optimized for
+ * callers that call this multiple times in a row.
+ *
+ * @ctx: Context for multiple DSI transactions
+ * @cmd: Command
+ * @seq: buffer containing data to be transmitted
+ */
+#define mipi_dsi_dcs_write_var_seq_multi(ctx, cmd, seq...)		\
+	do {								\
+		const u8 d[] = { cmd, seq };				\
+		mipi_dsi_dcs_write_buffer_multi(ctx, d, ARRAY_SIZE(d));	\
+	} while (0)
+
 /**
  * struct mipi_dsi_driver - DSI driver
  * @driver: device driver model driver
-- 
2.50.1

Hi,

On Mon, Jul 28, 2025 at 10:44 PM Brigham Campbell
<me@brighamcampbell.com> wrote:
>
> Create mipi_dsi_dcs_read_multi(), which accepts a mipi_dsi_multi_context
> struct for improved error handling and cleaner panel driver code.
>
> Create mipi_dsi_dcs_write_var_seq_multi() and
> mipi_dsi_generic_write_var_seq_multi() macros which allow MIPI panel
> drivers to write non-static data to display controllers.
>
> Signed-off-by: Brigham Campbell <me@brighamcampbell.com>
> ---
>
> I looked into using __builtin_constant_p() to extend
> mipi_dsi_{generic,dcs}_write_seq_multi() to accept both static and
> non-static sequences of bytes and store them accordingly, it looked
> promising at first, but I found no such solution ultimately. At the very
> least, if we find a solution at some point, my hope is that cocinelle
> could be used to replace each of the new var_seq_multi() usages among
> drivers with an improved seq_multi().
>
>
>  drivers/gpu/drm/drm_mipi_dsi.c | 37 ++++++++++++++++++++++++++++++++++
>  include/drm/drm_mipi_dsi.h     | 35 ++++++++++++++++++++++++++++++++
>  2 files changed, 72 insertions(+)

nit: maybe make the subject a bit more specific, like:

drm: Add MIPI _multi reader func and two new write variants


> @@ -415,6 +417,22 @@ void mipi_dsi_dcs_set_tear_off_multi(struct mipi_dsi_multi_context *ctx);
>                 mipi_dsi_generic_write_multi(ctx, d, ARRAY_SIZE(d)); \
>         } while (0)
>
> +/**
> + * mipi_dsi_generic_write_var_seq_multi - transmit non-static data using a
> + * generic write packet

nit: "non-constant", not "non-static"

From the caller's point of view the difference is that the data is
compile-time constant in one case and not compile-time constant in the
other case. It happens that means you can _store_ it in a "static
const" in one case and not in the other case, but that doesn't make
the parameters "static".


Other than nits:

Reviewed-by: Douglas Anderson <dianders@chromium.org>

On Tue Jul 29, 2025 at 3:34 PM MDT, Doug Anderson wrote:
>> +/**
>> + * mipi_dsi_generic_write_var_seq_multi - transmit non-static data using a
>> + * generic write packet
>
> nit: "non-constant", not "non-static"
>
> From the caller's point of view the difference is that the data is
> compile-time constant in one case and not compile-time constant in the
> other case. It happens that means you can _store_ it in a "static
> const" in one case and not in the other case, but that doesn't make
> the parameters "static".

Good point. The storage class is an important implementation detail
within drm_mipi_dsi.h, but just that from the perspective of a panel
driver author: an implementation detail. I'll go ahead and address this
and other feedback in v3.

Thanks,
Brigham