drm/bridge: Clear the DP_AUX_I2C_MOT bit passed in aux read command.

If the previous transfer didn't end with a command without DP_AUX_I2C_MOT,
the next read trasnfer will miss the first byte. But if the command in
previous transfer is requested with length 0, it's a no-op to anx7625
since it can't process this command. anx7625 requires the last command
to be read command with length > 0.

It's observed that if we clear the DP_AUX_I2C_MOT in read transfer, we
can still get correct data. Clear the read commands with DP_AUX_I2C_MOT
bit to fix this issue.

Fixes: adca62ec370c ("drm/bridge: anx7625: Support reading edid through aux channel")
Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
Reviewed-by: Xin Ji <xji@analogixsemi.com>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220217082224.1823916-1-hsinyi@chromium.org

diff --git a/drivers/gpu/drm/bridge/analogix/anx7625.c b/drivers/gpu/drm/bridge/analogix/anx7625.c
index 9aab879a885135a079307be43ef0f09b0d12713c..31ecf5626f1d98fa9ba35d1b2528616025b339fc 100644 (file)
--- a/drivers/gpu/drm/bridge/analogix/anx7625.c
+++ b/drivers/gpu/drm/bridge/analogix/anx7625.c
@@ -253,6 +253,8 @@ static int anx7625_aux_trans(struct anx7625_data *ctx, u8 op, u32 address,
        addrm = (address >> 8) & 0xFF;
        addrh = (address >> 16) & 0xFF;
 
+       if (!is_write)
+               op &= ~DP_AUX_I2C_MOT;
        cmd = DPCD_CMD(len, op);
 
        /* Set command and length */