[PATCH] drm/amdgpu: Always align dumb buffer at PAGE_SIZE

[Christian König]

I was thinking about that as well, yes.

Might be a good idea to just change the alignment check in 
amdgpu_bo_create():

                 /* Memory should be aligned at least to a page size. */
                 page_align = ALIGN(bp->byte_align, PAGE_SIZE) >> 
PAGE_SHIFT;


Something like ALIGN(bp->byte_align ?: 1, PAGE_SIZE) should already do it.

Christian.

Am 23.09.22 um 08:23 schrieb Marek Olšák:
> The kernel could report the true alignment from the ioctl instead of 0.
>
> Marek
>
> On Fri, Sep 23, 2022 at 1:31 AM Christian König 
> <christian.koenig at amd.com> wrote:
>
>     Am 23.09.22 um 07:28 schrieb lepton:
>     > On Thu, Sep 22, 2022 at 10:14 PM Christian König
>     > <christian.koenig at amd.com> wrote:
>     >> Am 23.09.22 um 01:04 schrieb Lepton Wu:
>     >>> Since size has been aligned to PAGE_SIZE already, just align it
>     >>> to PAGE_SIZE so later the buffer can be used as a texture in mesa
>     >>> after
>     https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fcgit.freedesktop.org%2Fmesa%2Fmesa%2Fcommit%2F%3Fid%3Df7a4051b8&data=05%7C01%7Cchristian.koenig%40amd.com%7C645f6878a7bd487588b708da9d246c4c%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637995077041120091%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=NMEAl8TByDLQFWW1d%2FaJfiGrXc4mpwL5dxNH0M0QH84%3D&reserved=0
>     <https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fcgit.freedesktop.org%2Fmesa%2Fmesa%2Fcommit%2F%3Fid%3Df7a4051b8&data=05%7C01%7Cchristian.koenig%40amd.com%7C69c0881fd97d4de3380408da9d2c336b%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637995111117539790%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=KMiCYD7blJCjO9zcfsqmy9%2FfYbtAmMHbrwpzHP7F5O0%3D&reserved=0>
>     >>> Otherwise, si_texture_create_object will fail at line
>     >>> "buf->alignment < tex->surface.alignment"
>     >> I don't think that those Mesa checks are a good idea in the
>     first place.
>     >>
>     >> The alignment value is often specified as zero when it doesn't
>     matter
>     >> because the minimum alignment can never be less than the page size.
>     > Are you suggesting to change those mesa checks?
>
>     Yes, the minimum alignment of allocations is always 4096 because
>     that's
>     the page size of the GPU.
>
>     > While that can be
>     > done, I still think a kernel side "fix" is still
>     > useful since it doesn't hurt while can fix issues for some
>     versions of mesa.
>
>     No, we have tons of places where we don't specify and alignment for
>     buffers because it never mattered. I certainly don't want to fix
>     all of
>     those.
>
>     Regards,
>     Christian.
>
>     >> Christian.
>     >>
>     >>> Signed-off-by: Lepton Wu <ytht.net at gmail.com>
>     >>> ---
>     >>>    drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c | 2 +-
>     >>>    1 file changed, 1 insertion(+), 1 deletion(-)
>     >>>
>     >>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
>     b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
>     >>> index 8ef31d687ef3b..8dca0c920d3ce 100644
>     >>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
>     >>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
>     >>> @@ -928,7 +928,7 @@ int amdgpu_mode_dumb_create(struct
>     drm_file *file_priv,
>     >>>        args->size = ALIGN(args->size, PAGE_SIZE);
>     >>>        domain = amdgpu_bo_get_preferred_domain(adev,
>     >>> amdgpu_display_supported_domains(adev, flags));
>     >>> -     r = amdgpu_gem_object_create(adev, args->size, 0,
>     domain, flags,
>     >>> +     r = amdgpu_gem_object_create(adev, args->size,
>     PAGE_SIZE, domain, flags,
>     >>>  ttm_bo_type_device, NULL, &gobj);
>     >>>        if (r)
>     >>>                return -ENOMEM;
>
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