drm/mcde: Retry DSI read/write transactions

The vendor driver makes a few retries on read DSI
transactions, something that is needed especially in
case of read (such as reading the panel MTP ID) while
the panel is running in video mode. This happens on
the Samsung s6e63m0 panel on the Golden device.

Retry reads and writes alike three times.

Signed-off-by: Linus Walleij <[e-mail]>
Reviewed-by: Stephan Gerhold <[e-mail]>
Cc: Stephan Gerhold <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/mcde/mcde_dsi.c

···
 	 (type == MIPI_DSI_GENERIC_READ_REQUEST_2_PARAM) || \
 	 (type == MIPI_DSI_DCS_READ))
 
+static int mcde_dsi_execute_transfer(struct mcde_dsi *d,
+				     const struct mipi_dsi_msg *msg)
+{
+	const u32 loop_delay_us = 10; /* us */
+	u32 loop_counter;
+	size_t txlen = msg->tx_len;
+	size_t rxlen = msg->rx_len;
+	int i;
+	u32 val;
+	int ret;
+
+	writel(~0, d->regs + DSI_DIRECT_CMD_STS_CLR);
+	writel(~0, d->regs + DSI_CMD_MODE_STS_CLR);
+	/* Send command */
+	writel(1, d->regs + DSI_DIRECT_CMD_SEND);
+
+	loop_counter = 1000 * 1000 / loop_delay_us;
+	if (MCDE_DSI_HOST_IS_READ(msg->type)) {
+		/* Read command */
+		while (!(readl(d->regs + DSI_DIRECT_CMD_STS) &
+			 (DSI_DIRECT_CMD_STS_READ_COMPLETED |
+			  DSI_DIRECT_CMD_STS_READ_COMPLETED_WITH_ERR))
+		       && --loop_counter)
+			usleep_range(loop_delay_us, (loop_delay_us * 3) / 2);
+		if (!loop_counter) {
+			dev_err(d->dev, "DSI read timeout!\n");
+			/* Set exit code and retry */
+			return -ETIME;
+		}
+	} else {
+		/* Writing only */
+		while (!(readl(d->regs + DSI_DIRECT_CMD_STS) &
+			 DSI_DIRECT_CMD_STS_WRITE_COMPLETED)
+		       && --loop_counter)
+			usleep_range(loop_delay_us, (loop_delay_us * 3) / 2);
+
+		if (!loop_counter) {
+			/* Set exit code and retry */
+			dev_err(d->dev, "DSI write timeout!\n");
+			return -ETIME;
+		}
+	}
+
+	val = readl(d->regs + DSI_DIRECT_CMD_STS);
+	if (val & DSI_DIRECT_CMD_STS_READ_COMPLETED_WITH_ERR) {
+		dev_err(d->dev, "read completed with error\n");
+		writel(1, d->regs + DSI_DIRECT_CMD_RD_INIT);
+		return -EIO;
+	}
+	if (val & DSI_DIRECT_CMD_STS_ACKNOWLEDGE_WITH_ERR_RECEIVED) {
+		val >>= DSI_DIRECT_CMD_STS_ACK_VAL_SHIFT;
+		dev_err(d->dev, "error during transmission: %04x\n",
+			val);
+		return -EIO;
+	}
+
+	if (!MCDE_DSI_HOST_IS_READ(msg->type)) {
+		/* Return number of bytes written */
+		ret = txlen;
+	} else {
+		/* OK this is a read command, get the response */
+		u32 rdsz;
+		u32 rddat;
+		u8 *rx = msg->rx_buf;
+
+		rdsz = readl(d->regs + DSI_DIRECT_CMD_RD_PROPERTY);
+		rdsz &= DSI_DIRECT_CMD_RD_PROPERTY_RD_SIZE_MASK;
+		rddat = readl(d->regs + DSI_DIRECT_CMD_RDDAT);
+		if (rdsz < rxlen) {
+			dev_err(d->dev, "read error, requested %zd got %d\n",
+				rxlen, rdsz);
+			return -EIO;
+		}
+		/* FIXME: read more than 4 bytes */
+		for (i = 0; i < 4 && i < rxlen; i++)
+			rx[i] = (rddat >> (i * 8)) & 0xff;
+		ret = rdsz;
+	}
+
+	/* Successful transmission */
+	return ret;
+}
+
 static ssize_t mcde_dsi_host_transfer(struct mipi_dsi_host *host,
 				      const struct mipi_dsi_msg *msg)
 {
 	struct mcde_dsi *d = host_to_mcde_dsi(host);
-	const u32 loop_delay_us = 10; /* us */
 	const u8 *tx = msg->tx_buf;
-	u32 loop_counter;
 	size_t txlen = msg->tx_len;
 	size_t rxlen = msg->rx_len;
+	unsigned int retries = 0;
 	u32 val;
 	int ret;
 	int i;
···
 		writel(val, d->regs + DSI_DIRECT_CMD_WRDAT3);
 	}
 
-	writel(~0, d->regs + DSI_DIRECT_CMD_STS_CLR);
-	writel(~0, d->regs + DSI_CMD_MODE_STS_CLR);
-	/* Send command */
-	writel(1, d->regs + DSI_DIRECT_CMD_SEND);
-
-	loop_counter = 1000 * 1000 / loop_delay_us;
-	if (MCDE_DSI_HOST_IS_READ(msg->type)) {
-		/* Read command */
-		while (!(readl(d->regs + DSI_DIRECT_CMD_STS) &
-			 (DSI_DIRECT_CMD_STS_READ_COMPLETED |
-			  DSI_DIRECT_CMD_STS_READ_COMPLETED_WITH_ERR))
-		       && --loop_counter)
-			usleep_range(loop_delay_us, (loop_delay_us * 3) / 2);
-		if (!loop_counter) {
-			dev_err(d->dev, "DSI read timeout!\n");
-			return -ETIME;
-		}
-	} else {
-		/* Writing only */
-		while (!(readl(d->regs + DSI_DIRECT_CMD_STS) &
-			 DSI_DIRECT_CMD_STS_WRITE_COMPLETED)
-		       && --loop_counter)
-			usleep_range(loop_delay_us, (loop_delay_us * 3) / 2);
-
-		if (!loop_counter) {
-			dev_err(d->dev, "DSI write timeout!\n");
-			return -ETIME;
-		}
+	while (retries < 3) {
+		ret = mcde_dsi_execute_transfer(d, msg);
+		if (ret >= 0)
+			break;
+		retries++;
 	}
+	if (ret < 0 && retries)
+		dev_err(d->dev, "gave up after %d retries\n", retries);
 
-	val = readl(d->regs + DSI_DIRECT_CMD_STS);
-	if (val & DSI_DIRECT_CMD_STS_READ_COMPLETED_WITH_ERR) {
-		dev_err(d->dev, "read completed with error\n");
-		writel(1, d->regs + DSI_DIRECT_CMD_RD_INIT);
-		return -EIO;
-	}
-	if (val & DSI_DIRECT_CMD_STS_ACKNOWLEDGE_WITH_ERR_RECEIVED) {
-		val >>= DSI_DIRECT_CMD_STS_ACK_VAL_SHIFT;
-		dev_err(d->dev, "error during transmission: %04x\n",
-			val);
-		return -EIO;
-	}
-
-	if (!MCDE_DSI_HOST_IS_READ(msg->type)) {
-		/* Return number of bytes written */
-		ret = txlen;
-	} else {
-		/* OK this is a read command, get the response */
-		u32 rdsz;
-		u32 rddat;
-		u8 *rx = msg->rx_buf;
-
-		rdsz = readl(d->regs + DSI_DIRECT_CMD_RD_PROPERTY);
-		rdsz &= DSI_DIRECT_CMD_RD_PROPERTY_RD_SIZE_MASK;
-		rddat = readl(d->regs + DSI_DIRECT_CMD_RDDAT);
-		if (rdsz < rxlen) {
-			dev_err(d->dev, "read error, requested %zd got %d\n",
-				rxlen, rdsz);
-			return -EIO;
-		}
-		/* FIXME: read more than 4 bytes */
-		for (i = 0; i < 4 && i < rxlen; i++)
-			rx[i] = (rddat >> (i * 8)) & 0xff;
-		ret = rdsz;
-	}
-
+	/* Clear any errors */
 	writel(~0, d->regs + DSI_DIRECT_CMD_STS_CLR);
 	writel(~0, d->regs + DSI_CMD_MODE_STS_CLR);