linux-kernel - Re: [PATCH v3] drm/i915/dp: Use max params for panels

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Date:   Thu, 26 Aug 2021 13:37:34 -0400
From:   Rodrigo Vivi <rodrigo.vivi@...el.com>
To:     Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc:     Kai-Heng Feng <kai.heng.feng@...onical.com>,
        jani.nikula@...ux.intel.com, joonas.lahtinen@...ux.intel.com,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Imre Deak <imre.deak@...el.com>,
        Uma Shankar <uma.shankar@...el.com>,
        Manasi Navare <manasi.d.navare@...el.com>,
        Ankit Nautiyal <ankit.k.nautiyal@...el.com>,
        José Roberto de Souza 
        <jose.souza@...el.com>, Sean Paul <seanpaul@...omium.org>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] drm/i915/dp: Use max params for panels < eDP 1.4

On Fri, Aug 20, 2021 at 08:26:14PM +0300, Ville Syrjälä wrote:
> On Fri, Aug 20, 2021 at 03:52:59PM +0800, Kai-Heng Feng wrote:
> > Users reported that after commit 2bbd6dba84d4 ("drm/i915: Try to use
> > fast+narrow link on eDP again and fall back to the old max strategy on
> > failure"), the screen starts to have wobbly effect.
> > 
> > Commit a5c936add6a2 ("drm/i915/dp: Use slow and wide link training for
> > everything") doesn't help either, that means the affected eDP 1.2 panels
> > only work with max params.
> > 
> > So use max params for panels < eDP 1.4 as Windows does to solve the
> > issue.
> > 
> > v3:
> >  - Do the eDP rev check in intel_edp_init_dpcd()
> > 
> > v2:
> >  - Check eDP 1.4 instead of DPCD 1.1 to apply max params
> > 
> > Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/3714
> > Fixes: 2bbd6dba84d4 ("drm/i915: Try to use fast+narrow link on eDP again and fall back to the old max strategy on failure")
> > Fixes: a5c936add6a2 ("drm/i915/dp: Use slow and wide link training for everything")
> > Suggested-by: Ville Syrjälä <ville.syrjala@...ux.intel.com>
> > Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
> 
> Slapped a cc:stable on it and pushed to drm-intel-next. Thanks.

Since I got a strange failure on CI_DIF_604 that I don't see on CI_DIF_603,
I'm avoiding the display patches. This one and also
dab1b47e57e0 ("drm/i915/dp: return proper DPRX link training result")

I know, it is probably the other one, but I had to remove both patches for
now and I'm not confident the CI will allow me to test with this one alone.

If we have -rc8 I will check again later. Otherwise we will have to send
to the stable mailing list later.

> 
> > ---
> >  drivers/gpu/drm/i915/display/intel_dp.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> > index 75d4ebc669411..e0dbd35ae7bc0 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > @@ -2445,11 +2445,14 @@ intel_edp_init_dpcd(struct intel_dp *intel_dp)
> >  	 */
> >  	if (drm_dp_dpcd_read(&intel_dp->aux, DP_EDP_DPCD_REV,
> >  			     intel_dp->edp_dpcd, sizeof(intel_dp->edp_dpcd)) ==
> > -			     sizeof(intel_dp->edp_dpcd))
> > +			     sizeof(intel_dp->edp_dpcd)) {
> >  		drm_dbg_kms(&dev_priv->drm, "eDP DPCD: %*ph\n",
> >  			    (int)sizeof(intel_dp->edp_dpcd),
> >  			    intel_dp->edp_dpcd);
> >  
> > +		intel_dp->use_max_params = intel_dp->edp_dpcd[0] < DP_EDP_14;
> > +	}
> > +
> >  	/*
> >  	 * This has to be called after intel_dp->edp_dpcd is filled, PSR checks
> >  	 * for SET_POWER_CAPABLE bit in intel_dp->edp_dpcd[1]
> > -- 
> > 2.32.0
> 
> -- 
> Ville Syrjälä
> Intel