Re: [PATCH v4] drm/msm/dp: force link training for display resolution change

[Kuogee Hsieh <quic_khsieh@quicinc.com>]

Any one has any comments?

Thanks,

On 5/27/2022 2:32 PM, Kuogee Hsieh wrote:
> During display resolution changes display have to be disabled first
> followed by display enabling with new resolution. Display disable
> will turn off both pixel clock and main link clock so that main link
> have to be re trained during display enable to have new video stream
> flow again. At current implementation, display enable function manually
> kicks up irq_hpd_handle which will read panel link status and start link
> training if link status is not in sync state. However, there is rare
> case that a particular panel links status keep staying in sync for
> some period of time after main link had been shut down previously at
> display disabled. Main link retraining will not be executed by
> irq_hdp_handle() if the link status read from pane shows it is in
> sync state. If this was happen, then video stream of newer display
> resolution will fail to be transmitted to panel due to main link is
> not in sync between host and panel. This patch force main link always
> be retrained during display enable procedure to prevent this rare
> failed case from happening. Also this implementation are more
> efficient than manual kicking off irq_hpd_handle function.
>
> Changes in v2:
> -- set force_link_train flag on DP only (is_edp == false)
>
> Changes in v3:
> -- revise commit  text
> -- add Fixes tag
>
> Changes in v4:
> -- revise commit  text
>
> Fixes: 62671d2ef24b ("drm/msm/dp: fixes wrong connection state caused by failure of link train")
> Signed-off-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
> ---
>   drivers/gpu/drm/msm/dp/dp_ctrl.c    |  6 +++---
>   drivers/gpu/drm/msm/dp/dp_ctrl.h    |  2 +-
>   drivers/gpu/drm/msm/dp/dp_display.c | 15 ++++++++-------
>   3 files changed, 12 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> index af7a80c..bea93eb 100644
> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> @@ -1551,7 +1551,7 @@ static int dp_ctrl_process_phy_test_request(struct dp_ctrl_private *ctrl)
>   
>   	ret = dp_ctrl_on_link(&ctrl->dp_ctrl);
>   	if (!ret)
> -		ret = dp_ctrl_on_stream(&ctrl->dp_ctrl);
> +		ret = dp_ctrl_on_stream(&ctrl->dp_ctrl, false);
>   	else
>   		DRM_ERROR("failed to enable DP link controller\n");
>   
> @@ -1807,7 +1807,7 @@ static int dp_ctrl_link_retrain(struct dp_ctrl_private *ctrl)
>   	return dp_ctrl_setup_main_link(ctrl, &training_step);
>   }
>   
> -int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl)
> +int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl, bool force_link_train)
>   {
>   	int ret = 0;
>   	bool mainlink_ready = false;
> @@ -1848,7 +1848,7 @@ int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl)
>   		return 0;
>   	}
>   
> -	if (!dp_ctrl_channel_eq_ok(ctrl))
> +	if (force_link_train || !dp_ctrl_channel_eq_ok(ctrl))
>   		dp_ctrl_link_retrain(ctrl);
>   
>   	/* stop txing train pattern to end link training */
> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.h b/drivers/gpu/drm/msm/dp/dp_ctrl.h
> index 0745fde..b563e2e 100644
> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.h
> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.h
> @@ -21,7 +21,7 @@ struct dp_ctrl {
>   };
>   
>   int dp_ctrl_on_link(struct dp_ctrl *dp_ctrl);
> -int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl);
> +int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl, bool force_link_train);
>   int dp_ctrl_off_link_stream(struct dp_ctrl *dp_ctrl);
>   int dp_ctrl_off_link(struct dp_ctrl *dp_ctrl);
>   int dp_ctrl_off(struct dp_ctrl *dp_ctrl);
> diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
> index c388323..370348d 100644
> --- a/drivers/gpu/drm/msm/dp/dp_display.c
> +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> @@ -872,7 +872,7 @@ static int dp_display_enable(struct dp_display_private *dp, u32 data)
>   		return 0;
>   	}
>   
> -	rc = dp_ctrl_on_stream(dp->ctrl);
> +	rc = dp_ctrl_on_stream(dp->ctrl, data);
>   	if (!rc)
>   		dp_display->power_on = true;
>   
> @@ -1654,6 +1654,7 @@ void dp_bridge_enable(struct drm_bridge *drm_bridge)
>   	int rc = 0;
>   	struct dp_display_private *dp_display;
>   	u32 state;
> +	bool force_link_train = false;
>   
>   	dp_display = container_of(dp, struct dp_display_private, dp_display);
>   	if (!dp_display->dp_mode.drm_mode.clock) {
> @@ -1688,10 +1689,14 @@ void dp_bridge_enable(struct drm_bridge *drm_bridge)
>   
>   	state =  dp_display->hpd_state;
>   
> -	if (state == ST_DISPLAY_OFF)
> +	if (state == ST_DISPLAY_OFF) {
>   		dp_display_host_phy_init(dp_display);
>   
> -	dp_display_enable(dp_display, 0);
> +		if (!dp->is_edp)
> +			force_link_train = true;
> +	}
> +
> +	dp_display_enable(dp_display, force_link_train);
>   
>   	rc = dp_display_post_enable(dp);
>   	if (rc) {
> @@ -1700,10 +1705,6 @@ void dp_bridge_enable(struct drm_bridge *drm_bridge)
>   		dp_display_unprepare(dp);
>   	}
>   
> -	/* manual kick off plug event to train link */
> -	if (state == ST_DISPLAY_OFF)
> -		dp_add_event(dp_display, EV_IRQ_HPD_INT, 0, 0);
> -
>   	/* completed connection */
>   	dp_display->hpd_state = ST_CONNECTED;
>