Re: [PATCH 5/6] drm/amdgpu/dm/mst: Report possible_crtcs incorrectly, for now

[Lyude Paul <lyude@redhat.com>]

a little late but: i915 does have this hack (or rather-possible_crtcs with MST
in i915 has been broken for a while and got fixed, but had to get reverted
because of this issue), it's where this originally came from.

On Wed, 2019-10-09 at 17:01 +0200, Daniel Vetter wrote:
> 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@redhat.com>
> > > Cc: Ville Syrjälä <ville.syrjala@linux.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
-- 
Cheers,
	Lyude Paul