linux-kernel - [PATCH v3 2/3] drm: Add MIPI read

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Message-ID: <20250730061748.1227643-3-me@brighamcampbell.com>
Date: Wed, 30 Jul 2025 00:17:47 -0600
From: Brigham Campbell <me@...ghamcampbell.com>
To: maarten.lankhorst@...ux.intel.com,
	mripard@...nel.org,
	tzimmermann@...e.de,
	airlied@...il.com,
	simona@...ll.ch,
	linus.walleij@...aro.org,
	neil.armstrong@...aro.org,
	jessica.zhang@....qualcomm.com,
	sam@...nborg.org
Cc: dianders@...omium.org,
	skhan@...uxfoundation.org,
	linux-kernel-mentees@...ts.linux.dev,
	dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org,
	Brigham Campbell <me@...ghamcampbell.com>
Subject: [PATCH v3 2/3] drm: Add MIPI read_multi func and two write macros

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@...omium.org>
Signed-off-by: Brigham Campbell <me@...ghamcampbell.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