drm/bridge/synopsys: dsi: Add read feature

This patch adds the DCS/GENERIC DSI read feature.
Signed-off-by: Philippe Cornu <philippe.cornu@st.com>
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180204213104.17834-1-philippe.cornu@st.com

drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c

@@ -391,18 +391,46 @@ static int dw_mipi_dsi_write(struct dw_mipi_dsi *dsi,
 	return dw_mipi_dsi_gen_pkt_hdr_write(dsi, le32_to_cpu(word));
 }
 
+static int dw_mipi_dsi_read(struct dw_mipi_dsi *dsi,
+			    const struct mipi_dsi_msg *msg)
+{
+	int i, j, ret, len = msg->rx_len;
+	u8 *buf = msg->rx_buf;
+	u32 val;
+
+	/* Wait end of the read operation */
+	ret = readl_poll_timeout(dsi->base + DSI_CMD_PKT_STATUS,
+				 val, !(val & GEN_RD_CMD_BUSY),
+				 1000, CMD_PKT_STATUS_TIMEOUT_US);
+	if (ret) {
+		dev_err(dsi->dev, "Timeout during read operation\n");
+		return ret;
+	}
+
+	for (i = 0; i < len; i += 4) {
+		/* Read fifo must not be empty before all bytes are read */
+		ret = readl_poll_timeout(dsi->base + DSI_CMD_PKT_STATUS,
+					 val, !(val & GEN_PLD_R_EMPTY),
+					 1000, CMD_PKT_STATUS_TIMEOUT_US);
+		if (ret) {
+			dev_err(dsi->dev, "Read payload FIFO is empty\n");
+			return ret;
+		}
+
+		val = dsi_read(dsi, DSI_GEN_PLD_DATA);
+		for (j = 0; j < 4 && j + i < len; j++)
+			buf[i + j] = val >> (8 * j);
+	}
+
+	return ret;
+}
+
 static ssize_t dw_mipi_dsi_host_transfer(struct mipi_dsi_host *host,
 					 const struct mipi_dsi_msg *msg)
 {
 	struct dw_mipi_dsi *dsi = host_to_dsi(host);
 	struct mipi_dsi_packet packet;
-	int ret;
-
-	if (msg->rx_buf || msg->rx_len) {
-		/* TODO dw drv improvements: implement read feature */
-		dev_warn(dsi->dev, "read operations not yet implemented\n");
-		return -EINVAL;
-	}
+	int ret, nb_bytes;
 
 	ret = mipi_dsi_create_packet(&packet, msg);
 	if (ret) {
@@ -416,12 +444,16 @@ static ssize_t dw_mipi_dsi_host_transfer(struct mipi_dsi_host *host,
 	if (ret)
 		return ret;
 
-	/*
-	 * TODO Only transmitted size is returned as actual driver does
-	 * not support dcs/generic reads. Please update return value when
-	 * delivering the read feature.
-	 */
-	return packet.size;
+	if (msg->rx_buf && msg->rx_len) {
+		ret = dw_mipi_dsi_read(dsi, msg);
+		if (ret)
+			return ret;
+		nb_bytes = msg->rx_len;
+	} else {
+		nb_bytes = packet.size;
+	}
+
+	return nb_bytes;
 }
 
 static const struct mipi_dsi_host_ops dw_mipi_dsi_host_ops = {