linux-kernel - Re: [PATCH v3 4/8] drm/msm/dp: Move link training to atomic

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Message-ID: <rwxrhtnft7xb2geu6sbyhkw7n6bu6em4aiag2glyhudmbt5cxa@wylxybjpfhkl>
Date: Thu, 15 Jan 2026 20:51:34 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Bjorn Andersson <andersson@...nel.org>
Cc: Rob Clark <robin.clark@....qualcomm.com>,
        Dmitry Baryshkov <lumag@...nel.org>,
        Abhinav Kumar <abhinav.kumar@...ux.dev>,
        Jessica Zhang <jesszhan0024@...il.com>, Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        Kuogee Hsieh <quic_khsieh@...cinc.com>, linux-arm-msm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org,
        Jessica Zhang <jessica.zhang@....qualcomm.com>
Subject: Re: [PATCH v3 4/8] drm/msm/dp: Move link training to atomic_enable()

On Thu, Jan 15, 2026 at 09:30:22AM -0600, Bjorn Andersson wrote:
> On Thu, Jan 15, 2026 at 09:29:09AM +0200, Dmitry Baryshkov wrote:
> > From: Jessica Zhang <jessica.zhang@....qualcomm.com>
> > 
> > Currently, the DP link training is being done during HPD. Move
> > link training to atomic_enable() in accordance with the atomic_enable()
> > documentation.
> > 
> > Link disabling is already done in atomic_post_disable() (as part of the
> > dp_ctrl_off_link_stream() helper).
> > 
> > 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>
> > Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
> 
> Reviewed-by: Bjorn Andersson <andersson@...nel.org>
> 
> > ---
> >  drivers/gpu/drm/msm/dp/dp_display.c | 11 ++++++-----
> >  1 file changed, 6 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
> > index a05144de3b93..3184066adb15 100644
> > --- a/drivers/gpu/drm/msm/dp/dp_display.c
> > +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> > @@ -436,11 +436,6 @@ 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);
> 
> I think unrelated to this patch (and series), but do we really want to
> keep the v_level and p_level settings until the user reconnects the
> cable?

Yes (or unless DP RX requires a full retraining). It's a part of the
standard.

> 
> Regards,
> Bjorn
> 
> > -	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);
> >  
> > @@ -1695,6 +1690,12 @@ 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);
> > +		drm_connector_set_link_status_property(dp->connector, DRM_LINK_STATUS_BAD);
> > +	}
> > +
> >  	msm_dp_display_enable(msm_dp_display, force_link_train);
> >  
> >  	rc = msm_dp_display_post_enable(dp);
> > 
> > -- 
> > 2.47.3
> > 
> > 

-- 
With best wishes
Dmitry