Re: [PATCH v4 05/39] drm/msm/dp: splite msm_dp_ctrl_config_ctrl() into link parts and stream parts

[Dmitry Baryshkov]

On Fri, Apr 10, 2026 at 05:33:40PM +0800, Yongxing Mou wrote:
> The DP_CONFIGURATION_CTRL register contains both link-level and
> stream-specific fields. Currently, msm_dp_ctrl_config_ctrl() configures
> all of them together. Separates the configuration into link parts and
> streams part for support MST.
> 
> Signed-off-by: Yongxing Mou <yongxing.mou@xxxxxxxxxxxxxxxx>
> ---
>  drivers/gpu/drm/msm/dp/dp_ctrl.c | 43 ++++++++++++++++++++++++++--------------
>  1 file changed, 28 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> index 476346e3ac19..85315467b5d0 100644
> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> @@ -388,26 +388,41 @@ void msm_dp_ctrl_push_idle(struct msm_dp_ctrl *msm_dp_ctrl)
>  	drm_dbg_dp(ctrl->drm_dev, "mainlink off\n");
>  }
>  
> -static void msm_dp_ctrl_config_ctrl(struct msm_dp_ctrl_private *ctrl)
> +static void msm_dp_ctrl_config_ctrl_streams(struct msm_dp_ctrl_private *ctrl,
> +					    struct msm_dp_panel *msm_dp_panel)
>  {
>  	u32 config = 0, tbd;
> +
> +	config = msm_dp_read_link(ctrl, REG_DP_CONFIGURATION_CTRL);
> +
> +	if (msm_dp_panel->msm_dp_mode.out_fmt_is_yuv_420)
> +		config |= DP_CONFIGURATION_CTRL_RGB_YUV; /* YUV420 */
> +
> +	tbd = msm_dp_link_get_test_bits_depth(ctrl->link,
> +					      msm_dp_panel->msm_dp_mode.bpp);
> +
> +	config |= tbd << DP_CONFIGURATION_CTRL_BPC_SHIFT;
> +
> +	if (msm_dp_panel->psr_cap.version)
> +		config |= DP_CONFIGURATION_CTRL_SEND_VSC;
> +
> +	drm_dbg_dp(ctrl->drm_dev, "stream DP_CONFIGURATION_CTRL=0x%x\n", config);
> +
> +	msm_dp_write_link(ctrl, REG_DP_CONFIGURATION_CTRL, config);

You have an RMW cycle here. Please document what prevents it from racing
with the concurrent msm_dp_ctrl_config_ctrl_link().

> +}
> +
> +static void msm_dp_ctrl_config_ctrl_link(struct msm_dp_ctrl_private *ctrl)
> +{
> +	u32 config = 0;
>  	const u8 *dpcd = ctrl->panel->dpcd;
>  
>  	/* Default-> LSCLK DIV: 1/4 LCLK  */
>  	config |= (2 << DP_CONFIGURATION_CTRL_LSCLK_DIV_SHIFT);
>  
> -	if (ctrl->panel->msm_dp_mode.out_fmt_is_yuv_420)
> -		config |= DP_CONFIGURATION_CTRL_RGB_YUV; /* YUV420 */
> -
>  	/* Scrambler reset enable */
>  	if (drm_dp_alternate_scrambler_reset_cap(dpcd))
>  		config |= DP_CONFIGURATION_CTRL_ASSR;
>  
> -	tbd = msm_dp_link_get_test_bits_depth(ctrl->link,
> -			ctrl->panel->msm_dp_mode.bpp);
> -
> -	config |= tbd << DP_CONFIGURATION_CTRL_BPC_SHIFT;
> -
>  	/* Num of Lanes */
>  	config |= ((ctrl->link->link_params.num_lanes - 1)
>  			<< DP_CONFIGURATION_CTRL_NUM_OF_LANES_SHIFT);
> @@ -421,10 +436,7 @@ static void msm_dp_ctrl_config_ctrl(struct msm_dp_ctrl_private *ctrl)
>  	config |= DP_CONFIGURATION_CTRL_STATIC_DYNAMIC_CN;
>  	config |= DP_CONFIGURATION_CTRL_SYNC_ASYNC_CLK;
>  
> -	if (ctrl->panel->psr_cap.version)
> -		config |= DP_CONFIGURATION_CTRL_SEND_VSC;
> -
> -	drm_dbg_dp(ctrl->drm_dev, "DP_CONFIGURATION_CTRL=0x%x\n", config);
> +	drm_dbg_dp(ctrl->drm_dev, "link DP_CONFIGURATION_CTRL=0x%x\n", config);
>  
>  	msm_dp_write_link(ctrl, REG_DP_CONFIGURATION_CTRL, config);
>  }
> @@ -450,7 +462,8 @@ static void msm_dp_ctrl_configure_source_params(struct msm_dp_ctrl_private *ctrl
>  	msm_dp_ctrl_lane_mapping(ctrl);
>  	msm_dp_setup_peripheral_flush(ctrl);
>  
> -	msm_dp_ctrl_config_ctrl(ctrl);
> +	msm_dp_ctrl_config_ctrl_link(ctrl);
> +	msm_dp_ctrl_config_ctrl_streams(ctrl, ctrl->panel);
>  
>  	test_bits_depth = msm_dp_link_get_test_bits_depth(ctrl->link, ctrl->panel->msm_dp_mode.bpp);
>  	colorimetry_cfg = msm_dp_link_get_colorimetry_config(ctrl->link);
> @@ -1628,7 +1641,7 @@ static int msm_dp_ctrl_link_train(struct msm_dp_ctrl_private *ctrl,
>  	u8 assr;
>  	struct msm_dp_link_info link_info = {0};
>  
> -	msm_dp_ctrl_config_ctrl(ctrl);
> +	msm_dp_ctrl_config_ctrl_link(ctrl);
>  
>  	link_info.num_lanes = ctrl->link->link_params.num_lanes;
>  	link_info.rate = ctrl->link->link_params.rate;
> 
> -- 
> 2.43.0
> 

-- 
With best wishes
Dmitry