[PATCH] drm/amdgpu: Clear VRAM for DRM dumb_create buffers

[Koenig, Christian]

Am 11.03.19 um 18:04 schrieb Kazlauskas, Nicholas:
> On 3/11/19 12:58 PM, Christian König wrote:
>> Am 08.03.19 um 17:47 schrieb Alex Deucher:
>>> On Fri, Mar 8, 2019 at 10:38 AM Nicholas Kazlauskas
>>> <nicholas.kazlauskas at amd.com> wrote:
>>>> The dumb_create API isn't intended for high performance rendering
>>>> and it's more useful for userspace (ie. IGT) to have them precleared.
>>>>
>>>> The bonus here is that we also won't needlessly leak whatever was
>>>> previously in VRAM, but it also probably wasn't sensitive if it was
>>>> going through this API.
>>>>
>>>> Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas at amd.com>
>>> Reviewed-by: Alex Deucher <alexander.deucher at amd.com>
>> NAK, IIRC we used to have this bit here before.
>>
>> In general I agree that this would be a good idea, but the problem is
>> the that first dump buffer is sometimes created before the engine
>> (usually SDMA) to clear VRAM is initialized.
>>
>> So you can run into a nice crash on suspend/resume.
>>
>> Christian.
> FWIW I never hit it myself during any suspend/resume tests I did but
> I'll take your word for it.
>
> How about doing a map/memset/unmap immediately after buffer creation
> here? It'd be much slower, but it's also what we'd be doing in userspace
> anyway.

And history repeat itself :) Yeah, that was also suggested before and 
didn't worked either for some reason.

But that was ~2 years ago and I really don't remember the details.

What could work is maybe to add a check if the engine is available if 
the flag is given and ignore it when it isn't.

Christian.

>
> Nicholas Kazlauskas
>
>
>>>> ---
>>>>    drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c | 3 ++-
>>>>    1 file changed, 2 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
>>>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
>>>> index fcaaac30e84b..a58072bbc9b8 100644
>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
>>>> @@ -743,7 +743,8 @@ int amdgpu_mode_dumb_create(struct drm_file
>>>> *file_priv,
>>>>           domain = amdgpu_bo_get_preferred_pin_domain(adev,
>>>>                                   
>>>> amdgpu_display_supported_domains(adev));
>>>>           r = amdgpu_gem_object_create(adev, args->size, 0, domain,
>>>> -
>>>> AMDGPU_GEM_CREATE_CPU_ACCESS_REQUIRED,
>>>> +
>>>> AMDGPU_GEM_CREATE_CPU_ACCESS_REQUIRED |
>>>> +                                    AMDGPU_GEM_CREATE_VRAM_CLEARED,
>>>>                                        ttm_bo_type_device, NULL, &gobj);
>>>>           if (r)
>>>>                   return -ENOMEM;
>>>> -- 
>>>> 2.17.1
>>>>
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