linux-kernel - Re: [PATCH 5/6] drm/amdgpu/dm/mst: Report possible

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Date:   Wed, 9 Oct 2019 17:01:55 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Sean Paul <sean@...rly.run>
Cc:     Lyude Paul <lyude@...hat.com>, amd-gfx@...ts.freedesktop.org,
        Ville Syrjälä 
        <ville.syrjala@...ux.intel.com>,
        Harry Wentland <harry.wentland@....com>,
        Leo Li <sunpeng.li@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "David (ChunMing) Zhou" <David1.Zhou@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Nicholas Kazlauskas <nicholas.kazlauskas@....com>,
        David Francis <David.Francis@....com>,
        Mario Kleiner <mario.kleiner.de@...il.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/6] drm/amdgpu/dm/mst: Report possible_crtcs
 incorrectly, for now

On Fri, Sep 27, 2019 at 11:27:41AM -0400, Sean Paul wrote:
> On Thu, Sep 26, 2019 at 06:51:07PM -0400, Lyude Paul wrote:
> > This commit is seperate from the previous one to make it easier to
> > revert in the future. Basically, there's multiple userspace applications
> > that interpret possible_crtcs very wrong:
> > 
> > https://gitlab.freedesktop.org/xorg/xserver/merge_requests/277
> > https://gitlab.gnome.org/GNOME/mutter/issues/759
> > 
> > While work is ongoing to fix these issues in userspace, we need to
> > report ->possible_crtcs incorrectly for now in order to avoid
> > introducing a regression in in userspace. Once these issues get fixed,
> > this commit should be reverted.
> > 
> > Signed-off-by: Lyude Paul <lyude@...hat.com>
> > Cc: Ville Syrjälä <ville.syrjala@...ux.intel.com>
> > ---
> >  drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> > index b404f1ae6df7..fe8ac801d7a5 100644
> > --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> > +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> > @@ -4807,6 +4807,17 @@ static int amdgpu_dm_crtc_init(struct amdgpu_display_manager *dm,
> >  	if (!acrtc->mst_encoder)
> >  		goto fail;
> >  
> > +	/*
> > +	 * FIXME: This is a hack to workaround the following issues:
> > +	 *
> > +	 * https://gitlab.gnome.org/GNOME/mutter/issues/759
> > +	 * https://gitlab.freedesktop.org/xorg/xserver/merge_requests/277
> > +	 *
> > +	 * One these issues are closed, this should be removed
> 
> Even when these issues are closed, we'll still be introducing a regression if we
> revert this change. Time for actually_possible_crtcs? :)
> 
> You also might want to briefly explain the u/s bug in case the links go sour.
> 
> > +	 */
> > +	acrtc->mst_encoder->base.possible_crtcs =
> > +		amdgpu_dm_get_encoder_crtc_mask(dm->adev);
> 
> Why don't we put this hack in amdgpu_dm_dp_create_fake_mst_encoder()?

If we don't have the same hack for i915 mst I think we shouldn't merge
this ... broken userspace is broken.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch