[PATCH v4 2/2] drm/amdgpu: Free VGA stolen memory as soon as possible.

[Michel Dänzer]

On 2018-04-12 03:33 PM, Alex Deucher wrote:
> On Thu, Apr 12, 2018 at 7:17 AM, Andrey Grodzovsky
> <Andrey.Grodzovsky at amd.com> wrote:
>> On 04/12/2018 12:32 AM, Alex Deucher wrote:
>>>
>>> On Thu, Apr 12, 2018 at 12:08 AM, Andrey Grodzovsky
>>> <andrey.grodzovsky at amd.com> wrote:
>>>>
>>>> Reserved VRAM is used to avoid overriding pre OS FB.
>>>> Once our display stack takes over we don't need the reserved
>>>> VRAM anymore.
>>>>
>>>> v2:
>>>> Remove comment, we know actually why we need to reserve the stolen VRAM.
>>>> Fix return type for amdgpu_ttm_late_init.
>>>> v3:
>>>> Return 0 in amdgpu_bo_late_init, rebase on changes to previous patch
>>>> v4:
>>>> Don't release stolen memory for GMC9 ASICs untill GART corruption
>>>> on S3 resume is resolved.
>>>>
>>>> Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky at amd.com>
>>>> Signed-off-by: Alex Deucher <alexander.deucher at amd.com>

[...]

>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c
>>>> b/drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c
>>>> index 252a6c69..099e3ce5 100644
>>>> --- a/drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c
>>>> +++ b/drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c
>>>> @@ -659,6 +659,16 @@ static int gmc_v9_0_late_init(void *handle)
>>>>          unsigned i;
>>>>          int r;
>>>>
>>>> +       /*
>>>> +        * TODO:
>>>> +        * Currently there is a bug where some memory client outside
>>>> +        * of the driver writes to first 8M of VRAM on S3 resume,
>>>> +        * this overrides GART which by default gets placed in first 8M
>>>> and
>>>> +        * causes VM_FAULTS once GTT is accessed.
>>>> +        * Keep the stolen memory reservation until this solved.
>>>> +        */
>>>> +       /* amdgpu_bo_late_init(adev); /
>>>> +
>>>
>>> We still need to free this somewhere.  I'd suggest calling it in
>>> gmc_v9_0_sw_fini() and add a comment there about moving it when we fix
>>> the issue.
>>>
>>>>          for(i = 0; i < adev->num_rings; ++i) {
>>>>                  struct amdgpu_ring *ring = adev->rings[i];
>>>>                  unsigned vmhub = ring->funcs->vmhub;
>>>> @@ -884,10 +894,6 @@ static int gmc_v9_0_sw_init(void *handle)
>>>>           */
>>>>          adev->gmc.mc_mask = 0xffffffffffffULL; /* 48 bit MC */
>>>>
>>>> -       /*
>>>> -        * It needs to reserve 8M stolen memory for vega10
>>>> -        * TODO: Figure out how to avoid that...
>>>> -        */
>>>>          adev->gmc.stolen_size = gmc_v9_0_get_vbios_fb_size(adev);
>>>
>>> We may also just want to return 8MB or 9MB temporarily in
>>> gmc_v9_0_get_vbios_fb_size until we sort out the root cause of the S3
>>> issue otherwise we're potentially wasting a lot more memory.
>>
>> But what if we have 4k display ? In this case returning 9M probably will not
>> hide the corruption  we were originally dealing with. I remember in that
>> case pre OS FB size would be 32M.
> 
> I guess it's a trade off, possible garbage monentary during bios to
> driver transition vs. wasting an additional 24 MB of CPU accessible
> vram for the life of the driver.

Can we free the reserved memory after initialization, then reserve it
again on resume?


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer