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.

Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Brigham Campbell <me@brighamcampbell.com>
---

Doug, you had suggested a slightly different shortlog for this patch. I
adjusted your suggestion to fit within the canonical recommended
shortlog length of 50 characters. I understand that the 50 character
limit isn't a rule as much as it is a guideline, but the current
shortlog seems to me like a good compromise.

 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..296ffdc9cd02 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-constant 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 Tue, Jul 29, 2025 at 11:18 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.
>
> Reviewed-by: Douglas Anderson <dianders@chromium.org>
> Signed-off-by: Brigham Campbell <me@brighamcampbell.com>
> ---
>
> Doug, you had suggested a slightly different shortlog for this patch. I
> adjusted your suggestion to fit within the canonical recommended
> shortlog length of 50 characters. I understand that the 50 character
> limit isn't a rule as much as it is a guideline, but the current
> shortlog seems to me like a good compromise.

Looks good.


> @@ -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

I should have been explicit, but the above "non-static" should also be
"non-constant". ;-)

I could probably fix that when applying, or you could send a v4. Up to you.

Speaking of applying this, I'll be on vacation next week, so I won't
be able to apply the patches until the week after. That will also give
anyone else on the list a chance to comment if they want...

-Doug

On Wed Jul 30, 2025 at 9:56 AM MDT, Doug Anderson wrote:
>> +/**
>> + * mipi_dsi_dcs_write_var_seq_multi - transmit a DCS command with non-static
>> + * payload
>
> I should have been explicit, but the above "non-static" should also be
> "non-constant". ;-)
>
> I could probably fix that when applying, or you could send a v4. Up to you.

Oops. This obviously needed to change as well, but I tunnel-visioned
hard. I'll go ahead and fix it in v4.

Naturally, I wouldn't be at all opposed to you or any other maintainer
making such a small change to one of my patches as it heads upstream,
but I'd rather not ask you to remember to make that change after a long
vacation and a busy merge window. There's no need for me to add even a
little more cognitive load to your job than what's necessary.

> Speaking of applying this, I'll be on vacation next week, so I won't
> be able to apply the patches until the week after. That will also give
> anyone else on the list a chance to comment if they want...

Awesome! I'll plan to sit tight and act on whatever feedback I get on
v4.

If you happen to be flying over northern Utah to get to your
destination, look out the window. I'll wave as you go by.

Cheers,
Brigham