This patch adds the DCS/GENERIC DSI read feature.

Signed-off-by: Philippe Cornu <philippe.co...@st.com>
---
Extra notes:
DSI read tests have been performed with DCS & GENERIC, short & long
commands, on two different panels.
The maximum fifo size (32*32-bit = 128 bytes on stm32) has been
verified too.

 drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c | 58 +++++++++++++++++++++------
 1 file changed, 45 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c 
b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
index e9422d05e897..65aeb3f78b48 100644
--- a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
@@ -397,18 +397,46 @@ 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) {
@@ -422,12 +450,16 @@ 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 = {
-- 
2.15.1

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