[PATCH v2 01/15] drm/dsi: Make mipi_dsi_dcs_{read, write}() symmetrical

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From: Thierry Reding <treding@xxxxxxxxxx>

Currently the mipi_dsi_dcs_write() function requires the DCS command
byte to be embedded within the write buffer whereas mipi_dsi_dcs_read()
has a separate parameter. Make them more symmetrical by adding an extra
command parameter to mipi_dsi_dcs_write().

The S6E8AA0 driver relies on the old asymmetric API and there's concern
that moving to the new API may be less efficient. Provide a new function
with the old semantics for those cases and make the S6E8AA0 driver use
it instead.

Signed-off-by: Thierry Reding <treding@xxxxxxxxxx>
---
Changes in v2:
- provide mipi_dsi_dcs_write_buffer() for backwards compatibility

 drivers/gpu/drm/drm_mipi_dsi.c        | 127 +++++++++++++++++++++++++++++-----
 drivers/gpu/drm/panel/panel-s6e8aa0.c |   2 +-
 include/drm/drm_mipi_dsi.h            |   6 +-
 3 files changed, 114 insertions(+), 21 deletions(-)

diff --git a/drivers/gpu/drm/drm_mipi_dsi.c b/drivers/gpu/drm/drm_mipi_dsi.c
index eb6dfe52cab2..1702ffd07986 100644
--- a/drivers/gpu/drm/drm_mipi_dsi.c
+++ b/drivers/gpu/drm/drm_mipi_dsi.c
@@ -199,33 +199,120 @@ int mipi_dsi_detach(struct mipi_dsi_device *dsi)
 EXPORT_SYMBOL(mipi_dsi_detach);
 
 /**
- * mipi_dsi_dcs_write - send DCS write command
- * @dsi: DSI device
- * @data: pointer to the command followed by parameters
- * @len: length of @data
+ * mipi_dsi_dcs_write_buffer() - transmit a DCS command with payload
+ * @dsi: DSI peripheral device
+ * @data: buffer containing data to be transmitted
+ * @len: size of transmission buffer
+ *
+ * This function will automatically choose the right data type depending on
+ * the command payload length.
+ *
+ * Return: The number of bytes successfully transmitted or a negative error
+ * code on failure.
  */
-ssize_t mipi_dsi_dcs_write(struct mipi_dsi_device *dsi, const void *data,
-			    size_t len)
+ssize_t mipi_dsi_dcs_write_buffer(struct mipi_dsi_device *dsi,
+				  const void *data, size_t len)
 {
-	const struct mipi_dsi_host_ops *ops = dsi->host->ops;
 	struct mipi_dsi_msg msg = {
 		.channel = dsi->channel,
 		.tx_buf = data,
 		.tx_len = len
 	};
 
-	if (!ops || !ops->transfer)
+	if (!dsi->host->ops || !dsi->host->ops->transfer)
 		return -ENOSYS;
 
 	switch (len) {
 	case 0:
 		return -EINVAL;
+
 	case 1:
 		msg.type = MIPI_DSI_DCS_SHORT_WRITE;
 		break;
+
 	case 2:
 		msg.type = MIPI_DSI_DCS_SHORT_WRITE_PARAM;
 		break;
+
+	default:
+		msg.type = MIPI_DSI_DCS_LONG_WRITE;
+		break;
+	}
+
+	return dsi->host->ops->transfer(dsi->host, &msg);
+}
+EXPORT_SYMBOL(mipi_dsi_dcs_write_buffer);
+
+/**
+ * mipi_dsi_dcs_write() - send DCS write command
+ * @dsi: DSI peripheral device
+ * @cmd: DCS command
+ * @data: buffer containing the command payload
+ * @len: command payload length
+ *
+ * This function will automatically choose the right data type depending on
+ * the command payload length.
+ *
+ * Return: The number of bytes successfully transmitted or a negative error
+ * code on failure.
+ */
+ssize_t mipi_dsi_dcs_write(struct mipi_dsi_device *dsi, u8 cmd,
+			   const void *data, size_t len)
+{
+	struct mipi_dsi_msg msg;
+	ssize_t err;
+	size_t size;
+	u8 *tx;
+
+	if (!dsi->host->ops || !dsi->host->ops->transfer)
+		return -ENOSYS;
+
+	if (len > 0) {
+		unsigned int offset = 0;
+
+		/*
+		 * DCS long write packets contain the word count in the header
+		 * bytes 1 and 2 and have a payload containing the DCS command
+		 * byte folowed by word count minus one bytes.
+		 *
+		 * DCS short write packets encode the DCS command and up to
+		 * one parameter in header bytes 1 and 2.
+		 */
+		if (len > 1)
+			size = 3 + len;
+		else
+			size = 1 + len;
+
+		tx = kmalloc(size, GFP_KERNEL);
+		if (!tx)
+			return -ENOMEM;
+
+		/* write word count to header for DCS long write packets */
+		if (len > 1) {
+			tx[offset++] = ((1 + len) >> 0) & 0xff;
+			tx[offset++] = ((1 + len) >> 8) & 0xff;
+		}
+
+		/* write the DCS command byte followed by the payload */
+		tx[offset++] = cmd;
+		memcpy(tx + offset, data, len);
+	} else {
+		tx = &cmd;
+		size = 1;
+	}
+
+	memset(&msg, 0, sizeof(msg));
+	msg.channel = dsi->channel;
+	msg.tx_len = size;
+	msg.tx_buf = tx;
+
+	switch (len) {
+	case 0:
+		msg.type = MIPI_DSI_DCS_SHORT_WRITE;
+		break;
+	case 1:
+		msg.type = MIPI_DSI_DCS_SHORT_WRITE_PARAM;
+		break;
 	default:
 		msg.type = MIPI_DSI_DCS_LONG_WRITE;
 		break;
@@ -234,23 +321,27 @@ ssize_t mipi_dsi_dcs_write(struct mipi_dsi_device *dsi, const void *data,
 	if (dsi->mode_flags & MIPI_DSI_MODE_LPM)
 		msg.flags = MIPI_DSI_MSG_USE_LPM;
 
-	return ops->transfer(dsi->host, &msg);
+	err = dsi->host->ops->transfer(dsi->host, &msg);
+
+	if (len > 0)
+		kfree(tx);
+
+	return err;
 }
 EXPORT_SYMBOL(mipi_dsi_dcs_write);
 
 /**
- * mipi_dsi_dcs_read - send DCS read request command
- * @dsi: DSI device
- * @cmd: DCS read command
- * @data: pointer to read buffer
- * @len: length of @data
+ * mipi_dsi_dcs_read() - send DCS read request command
+ * @dsi: DSI peripheral device
+ * @cmd: DCS command
+ * @data: buffer in which to receive data
+ * @len: size of receive buffer
  *
- * Function returns number of read bytes or error code.
+ * Return: The number of bytes read or a negative error code on failure.
  */
 ssize_t mipi_dsi_dcs_read(struct mipi_dsi_device *dsi, u8 cmd, void *data,
 			  size_t len)
 {
-	const struct mipi_dsi_host_ops *ops = dsi->host->ops;
 	struct mipi_dsi_msg msg = {
 		.channel = dsi->channel,
 		.type = MIPI_DSI_DCS_READ,
@@ -260,13 +351,13 @@ ssize_t mipi_dsi_dcs_read(struct mipi_dsi_device *dsi, u8 cmd, void *data,
 		.rx_len = len
 	};
 
-	if (!ops || !ops->transfer)
+	if (!dsi->host->ops || !dsi->host->ops->transfer)
 		return -ENOSYS;
 
 	if (dsi->mode_flags & MIPI_DSI_MODE_LPM)
 		msg.flags = MIPI_DSI_MSG_USE_LPM;
 
-	return ops->transfer(dsi->host, &msg);
+	return dsi->host->ops->transfer(dsi->host, &msg);
 }
 EXPORT_SYMBOL(mipi_dsi_dcs_read);
 
diff --git a/drivers/gpu/drm/panel/panel-s6e8aa0.c b/drivers/gpu/drm/panel/panel-s6e8aa0.c
index b5217fe37f02..0f85a7c37687 100644
--- a/drivers/gpu/drm/panel/panel-s6e8aa0.c
+++ b/drivers/gpu/drm/panel/panel-s6e8aa0.c
@@ -141,7 +141,7 @@ static void s6e8aa0_dcs_write(struct s6e8aa0 *ctx, const void *data, size_t len)
 	if (ctx->error < 0)
 		return;
 
-	ret = mipi_dsi_dcs_write(dsi, data, len);
+	ret = mipi_dsi_dcs_write_buffer(dsi, data, len);
 	if (ret < 0) {
 		dev_err(ctx->dev, "error %zd writing dcs seq: %*ph\n", ret, len,
 			data);
diff --git a/include/drm/drm_mipi_dsi.h b/include/drm/drm_mipi_dsi.h
index 8569dc5a1026..ccc3869e137b 100644
--- a/include/drm/drm_mipi_dsi.h
+++ b/include/drm/drm_mipi_dsi.h
@@ -132,8 +132,10 @@ static inline struct mipi_dsi_device *to_mipi_dsi_device(struct device *dev)
 
 int mipi_dsi_attach(struct mipi_dsi_device *dsi);
 int mipi_dsi_detach(struct mipi_dsi_device *dsi);
-ssize_t mipi_dsi_dcs_write(struct mipi_dsi_device *dsi, const void *data,
-			    size_t len);
+ssize_t mipi_dsi_dcs_write_buffer(struct mipi_dsi_device *dsi,
+				  const void *data, size_t len);
+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);
 
-- 
2.1.2

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