[PATCH v2] drm/msm/dsi: use RMW cycles in dsi_update_dsc_timing

[Abhinav Kumar]

On 4/30/2022 10:55 AM, Dmitry Baryshkov wrote:
> The downstream uses read-modify-write for updating command mode
> compression registers. Let's follow this approach. This also fixes the
> following warning:
> 
> drivers/gpu/drm/msm/dsi/dsi_host.c:918:23: warning: variable 'reg_ctrl' set but not used [-Wunused-but-set-variable]
> 
> Reported-by: kernel test robot <lkp at intel.com>
> Fixes: 08802f515c3c ("drm/msm/dsi: Add support for DSC configuration")
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov at linaro.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk at quicinc.com>
> ---
> 
> Changes since v1:
>   - Fix c&p error and apply mask clear to reg_ctrl2 instead of reg_ctrl
>     (Abhinav)
> 
> ---
>   drivers/gpu/drm/msm/dsi/dsi_host.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
> index c983698d1384..a95d5df52653 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> @@ -961,10 +961,13 @@ static void dsi_update_dsc_timing(struct msm_dsi_host *msm_host, bool is_cmd_mod
>   		reg_ctrl = dsi_read(msm_host, REG_DSI_COMMAND_COMPRESSION_MODE_CTRL);
>   		reg_ctrl2 = dsi_read(msm_host, REG_DSI_COMMAND_COMPRESSION_MODE_CTRL2);
>   
> +		reg_ctrl &= ~0xffff;
>   		reg_ctrl |= reg;
> +
> +		reg_ctrl2 &= ~DSI_COMMAND_COMPRESSION_MODE_CTRL2_STREAM0_SLICE_WIDTH__MASK;
>   		reg_ctrl2 |= DSI_COMMAND_COMPRESSION_MODE_CTRL2_STREAM0_SLICE_WIDTH(bytes_in_slice);
>   
> -		dsi_write(msm_host, REG_DSI_COMMAND_COMPRESSION_MODE_CTRL, reg);
> +		dsi_write(msm_host, REG_DSI_COMMAND_COMPRESSION_MODE_CTRL, reg_ctrl);
>   		dsi_write(msm_host, REG_DSI_COMMAND_COMPRESSION_MODE_CTRL2, reg_ctrl2);
>   	} else {
>   		dsi_write(msm_host, REG_DSI_VIDEO_COMPRESSION_MODE_CTRL, reg);