linux-kernel - Re: [PATCH 18/19] drm/msm/dp: Move link training to atomic

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Message-ID: <cofa377vptj7on637u3c3mnxndplcmaegsb5h6idinz5wrvm6s@toylno4uapq4>
Date: Mon, 14 Jul 2025 14:54:12 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Jessica Zhang <jessica.zhang@....qualcomm.com>
Cc: Rob Clark <robin.clark@....qualcomm.com>,
        Abhinav Kumar <abhinav.kumar@...ux.dev>,
        Dmitry Baryshkov <lumag@...nel.org>, Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Yongxing Mou <quic_yongmou@...cinc.com>
Subject: Re: [PATCH 18/19] drm/msm/dp: Move link training to atomic_enable()

On Fri, Jul 11, 2025 at 05:58:23PM -0700, Jessica Zhang wrote:
> Currently, the DP link training is being done during HPD. Move
> link training to atomic_enable() in accordance with the atomic_enable()
> documentation.
> 
> In addition, don't disable the link until atomic_post_disable() (as part
> of the dp_ctrl_off[_link_stream]() helpers).
> 
> Since the link training is moved to a later part of the enable sequence,
> change the bridge detect() to return true when the display is physically
> connected instead of when the link is ready.

These two parts should be patch #2 in the series.

> 
> Finally, call the plug/unplug handlers directly in hpd_notify() instead
> of queueing them in the event thread so that they aren't preempted by
> other events.
> 
> Signed-off-by: Jessica Zhang <jessica.zhang@....qualcomm.com>
> ---
>  drivers/gpu/drm/msm/dp/dp_display.c | 15 ++++++++-------
>  drivers/gpu/drm/msm/dp/dp_drm.c     |  6 +++---
>  2 files changed, 11 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
> index 87f2750a99ca..32e1ee40c2c3 100644
> --- a/drivers/gpu/drm/msm/dp/dp_display.c
> +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> @@ -410,11 +410,6 @@ static int msm_dp_display_process_hpd_high(struct msm_dp_display_private *dp)
>  	msm_dp_link_psm_config(dp->link, &dp->panel->link_info, false);
>  
>  	msm_dp_link_reset_phy_params_vx_px(dp->link);
> -	rc = msm_dp_ctrl_on_link(dp->ctrl);
> -	if (rc) {
> -		DRM_ERROR("failed to complete DP link training\n");
> -		goto end;
> -	}
>  
>  	msm_dp_add_event(dp, EV_USER_NOTIFICATION, true, 0);
>  
> @@ -1561,6 +1556,12 @@ void msm_dp_bridge_atomic_enable(struct drm_bridge *drm_bridge,
>  		force_link_train = true;
>  	}
>  
> +	rc = msm_dp_ctrl_on_link(msm_dp_display->ctrl);
> +	if (rc) {
> +		DRM_ERROR("Failed link training (rc=%d)\n", rc);
> +		dp->connector->state->link_status = DRM_LINK_STATUS_BAD;
> +	}
> +
>  	msm_dp_display_enable(msm_dp_display, force_link_train);
>  
>  	rc = msm_dp_display_post_enable(dp);
> @@ -1706,7 +1707,7 @@ void msm_dp_bridge_hpd_notify(struct drm_bridge *bridge,
>  		return;
>  
>  	if (!msm_dp_display->link_ready && status == connector_status_connected)
> -		msm_dp_add_event(dp, EV_HPD_PLUG_INT, 0, 0);
> +		msm_dp_hpd_plug_handle(dp, 0);
>  	else if (msm_dp_display->link_ready && status == connector_status_disconnected)
> -		msm_dp_add_event(dp, EV_HPD_UNPLUG_INT, 0, 0);
> +		msm_dp_hpd_unplug_handle(dp, 0);

This chunk should be separated from this patch. I'd ask to drop
EV_HPD_PLUG_INT / EV_HPD_UNPLUG_INT completely and call DRM functions
all over the place instead. You can do it in a single patch, which comes
after this one.

>  }

-- 
With best wishes
Dmitry