linux-kernel - Re: [PATCH] drm/amdgpu: Raven: don't allow mixing GTT and VRAM

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Message-ID: <CADnq5_OeTJqzg0DgV06b-u_AmgaqXL5XWdQ6h40zcgGj1mCE_A@mail.gmail.com>
Date: Wed, 16 Jul 2025 17:02:59 -0400
From: Alex Deucher <alexdeucher@...il.com>
To: Brian Geffon <bgeffon@...gle.com>, "Wentland, Harry" <Harry.Wentland@....com>, 
	"Leo (Sunpeng) Li" <Sunpeng.Li@....com>
Cc: Alex Deucher <alexander.deucher@....com>, christian.koenig@....com, 
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
	Tvrtko Ursulin <tvrtko.ursulin@...lia.com>, Yunxiang Li <Yunxiang.Li@....com>, 
	Lijo Lazar <lijo.lazar@....com>, Prike Liang <Prike.Liang@....com>, 
	Pratap Nirujogi <pratap.nirujogi@....com>, Luben Tuikov <luben.tuikov@....com>, 
	amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org, 
	linux-kernel@...r.kernel.org, Garrick Evans <garrick@...gle.com>, 
	Thadeu Lima de Souza Cascardo <cascardo@...lia.com>, stable@...r.kernel.org
Subject: Re: [PATCH] drm/amdgpu: Raven: don't allow mixing GTT and VRAM

On Wed, Jul 16, 2025 at 12:40 PM Brian Geffon <bgeffon@...gle.com> wrote:
>
> On Wed, Jul 16, 2025 at 12:33 PM Alex Deucher <alexdeucher@...il.com> wrote:
> >
> > On Wed, Jul 16, 2025 at 12:18 PM Brian Geffon <bgeffon@...gle.com> wrote:
> > >
> > > Commit 81d0bcf99009 ("drm/amdgpu: make display pinning more flexible (v2)")
> > > allowed for newer ASICs to mix GTT and VRAM, this change also noted that
> > > some older boards, such as Stoney and Carrizo do not support this.
> > > It appears that at least one additional ASIC does not support this which
> > > is Raven.
> > >
> > > We observed this issue when migrating a device from a 5.4 to 6.6 kernel
> > > and have confirmed that Raven also needs to be excluded from mixing GTT
> > > and VRAM.
> >
> > Can you elaborate a bit on what the problem is?  For carrizo and
> > stoney this is a hardware limitation (all display buffers need to be
> > in GTT or VRAM, but not both).  Raven and newer don't have this
> > limitation and we tested raven pretty extensively at the time.
>
> Thanks for taking the time to look. We have automated testing and a
> few igt gpu tools tests failed and after debugging we found that
> commit 81d0bcf99009 is what introduced the failures on this hardware
> on 6.1+ kernels. The specific tests that fail are kms_async_flips and
> kms_plane_alpha_blend, excluding Raven from this sharing of GTT and
> VRAM buffers resolves the issue.

+ Harry and Leo

This sounds like the memory placement issue we discussed last week.
In that case, the issue is related to where the buffer ends up when we
try to do an async flip.  In that case, we can't do an async flip
without a full modeset if the buffers locations are different than the
last modeset because we need to update more than just the buffer base
addresses.  This change works around that limitation by always forcing
display buffers into VRAM or GTT.  Adding raven to this case may fix
those tests but will make the overall experience worse because we'll
end up effectively not being able to not fully utilize both gtt and
vram for display which would reintroduce all of the problems fixed by
81d0bcf99009 ("drm/amdgpu: make display pinning more flexible (v2)").

Alex

>
> Brian
>
> >
> >
> > Alex
> >
> > >
> > > Fixes: 81d0bcf99009 ("drm/amdgpu: make display pinning more flexible (v2)")
> > > Cc: Luben Tuikov <luben.tuikov@....com>
> > > Cc: Christian König <christian.koenig@....com>
> > > Cc: Alex Deucher <alexander.deucher@....com>
> > > Cc: stable@...r.kernel.org # 6.1+
> > > Tested-by: Thadeu Lima de Souza Cascardo <cascardo@...lia.com>
> > > Signed-off-by: Brian Geffon <bgeffon@...gle.com>
> > > ---
> > >  drivers/gpu/drm/amd/amdgpu/amdgpu_object.c | 3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
> > > index 73403744331a..5d7f13e25b7c 100644
> > > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
> > > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
> > > @@ -1545,7 +1545,8 @@ uint32_t amdgpu_bo_get_preferred_domain(struct amdgpu_device *adev,
> > >                                             uint32_t domain)
> > >  {
> > >         if ((domain == (AMDGPU_GEM_DOMAIN_VRAM | AMDGPU_GEM_DOMAIN_GTT)) &&
> > > -           ((adev->asic_type == CHIP_CARRIZO) || (adev->asic_type == CHIP_STONEY))) {
> > > +           ((adev->asic_type == CHIP_CARRIZO) || (adev->asic_type == CHIP_STONEY) ||
> > > +            (adev->asic_type == CHIP_RAVEN))) {
> > >                 domain = AMDGPU_GEM_DOMAIN_VRAM;
> > >                 if (adev->gmc.real_vram_size <= AMDGPU_SG_THRESHOLD)
> > >                         domain = AMDGPU_GEM_DOMAIN_GTT;
> > > --
> > > 2.50.0.727.gbf7dc18ff4-goog
> > >