linux-kernel - Re: [PATCH] drm/i915/psr: Disable PSR2 selective fetch for all TGL steps

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Date:   Tue, 08 Feb 2022 13:09:10 -0500
From:   Lyude Paul <lyude@...hat.com>
To:     "Souza, Jose" <jose.souza@...el.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>
Cc:     "airlied@...ux.ie" <airlied@...ux.ie>,
        "ville.syrjala@...ux.intel.com" <ville.syrjala@...ux.intel.com>,
        "Vivi, Rodrigo" <rodrigo.vivi@...el.com>,
        "joonas.lahtinen@...ux.intel.com" <joonas.lahtinen@...ux.intel.com>,
        "Mun, Gwan-gyeong" <gwan-gyeong.mun@...el.com>,
        "Roper, Matthew D" <matthew.d.roper@...el.com>,
        "tvrtko.ursulin@...ux.intel.com" <tvrtko.ursulin@...ux.intel.com>,
        "Kahola, Mika" <mika.kahola@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "jani.nikula@...ux.intel.com" <jani.nikula@...ux.intel.com>,
        "daniel@...ll.ch" <daniel@...ll.ch>,
        "Hogander, Jouni" <jouni.hogander@...el.com>,
        "De Marchi, Lucas" <lucas.demarchi@...el.com>
Subject: Re: [PATCH] drm/i915/psr: Disable PSR2 selective fetch for all TGL
 steps

On Tue, 2022-02-08 at 13:06 +0000, Souza, Jose wrote:
> On Mon, 2022-02-07 at 16:38 -0500, Lyude Paul wrote:
> > As we've unfortunately started to come to expect from PSR on Intel
> > platforms, PSR2 selective fetch is not at all ready to be enabled on
> > Tigerlake as it results in severe flickering issues - at least on this
> > ThinkPad X1 Carbon 9th generation. The easiest way I've found of
> > reproducing these issues is to just move the cursor around the left border
> > of the screen (suspicious…).
> 
> Where is the bug for that? Where is the logs?

I'm happy to open up a bug and include some logs, will do it in just a moment

> We can't go from enabled to disabled without any debug and because of a
> single device.
> In the mean time you have the option to set the i915 parameter to disable
> it.

I mean - I totally understand the hesistance with the lack of debug info, I'll
go open up an issue with said info in a bit. FWIW is a machine currently being
sold with Linux pre-installs which is expected to work out of the box, so it's
not exactly an uncommon laptop to be running Linux. Also I don't have any
problem with us trying to fix the issue before flat out disabling things - I
sent the revert hoping that would happen, and also because I needed to write
the revert anyway since I had to disable this in Fedora's kernel.

> 
> > 
> > So, fix people's displays again and turn PSR2 selective fetch off for all
> > steppings of Tigerlake. This can be re-enabled again if someone from Intel
> > finds the time to fix this functionality on OEM machines.
> > 
> > Signed-off-by: Lyude Paul <lyude@...hat.com>
> > Fixes: 7f6002e58025 ("drm/i915/display: Enable PSR2 selective fetch by
> > default")
> > Cc: Gwan-gyeong Mun <gwan-gyeong.mun@...el.com>
> > Cc: Ville Syrjälä <ville.syrjala@...ux.intel.com>
> > Cc: José Roberto de Souza <jose.souza@...el.com>
> > Cc: Jani Nikula <jani.nikula@...ux.intel.com>
> > Cc: Rodrigo Vivi <rodrigo.vivi@...el.com>
> > Cc: intel-gfx@...ts.freedesktop.org
> > Cc: <stable@...r.kernel.org> # v5.16+
> > ---
> >  drivers/gpu/drm/i915/display/intel_psr.c | 10 +++++++---
> >  1 file changed, 7 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_psr.c
> > b/drivers/gpu/drm/i915/display/intel_psr.c
> > index a1a663f362e7..25c16abcd9cd 100644
> > --- a/drivers/gpu/drm/i915/display/intel_psr.c
> > +++ b/drivers/gpu/drm/i915/display/intel_psr.c
> > @@ -737,10 +737,14 @@ static bool intel_psr2_sel_fetch_config_valid(struct
> > intel_dp *intel_dp,
> >                 return false;
> >         }
> >  
> > -       /* Wa_14010254185 Wa_14010103792 */
> > -       if (IS_TGL_DISPLAY_STEP(dev_priv, STEP_A0, STEP_C0)) {
> > +       /*
> > +        * There's two things stopping this from being enabled on TGL:
> > +        * For steps A0-C0: workarounds Wa_14010254185 Wa_14010103792 are
> > missing
> > +        * For all steps: PSR2 selective fetch causes screen flickering
> > +        */
> > +       if (IS_TIGERLAKE(dev_priv)) {
> >                 drm_dbg_kms(&dev_priv->drm,
> > -                           "PSR2 sel fetch not enabled, missing the
> > implementation of WAs\n");
> > +                           "PSR2 sel fetch not enabled, currently broken
> > on TGL\n");
> >                 return false;
> >         }
> >  
> 

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat