[PATCH 1/2] drm/amdgpu/gmc: always steal the first 32MB of vram for fw hand-over

[Christian König]

Am 06.04.2018 um 09:50 schrieb Michel Dänzer:
> On 2018-04-05 09:27 PM, Alex Deucher wrote:
>> On Thu, Apr 5, 2018 at 2:26 PM, Andrey Grodzovsky
>> <andrey.grodzovsky at amd.com> wrote:
>>> From: Alex Deucher <alexander.deucher at amd.com>
>>>
>>> The vbios uses memory from the start of vram for the pre-OS
>>> framebuffer. Reserve this at driver load time to prevent
>>> the driver from using it for other things which may cause
>>> atrifacts on screen before the console has kicked in.
>>>
>>> Signed-off-by: Alex Deucher <alexander.deucher at amd.com>
>>> Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky at amd.com>
> [...]
>
>>> diff --git a/drivers/gpu/drm/amd/amdgpu/gmc_v8_0.c b/drivers/gpu/drm/amd/amdgpu/gmc_v8_0.c
>>> index d71d4cb..c8c5ca2 100644
>>> --- a/drivers/gpu/drm/amd/amdgpu/gmc_v8_0.c
>>> +++ b/drivers/gpu/drm/amd/amdgpu/gmc_v8_0.c
>>> @@ -1096,7 +1096,7 @@ static int gmc_v8_0_sw_init(void *handle)
>>>           */
>>>          adev->gmc.mc_mask = 0xffffffffffULL; /* 40 bit MC */
>>>
>>> -       adev->gmc.stolen_size = 256 * 1024;
>>> +       adev->gmc.stolen_size = 32 * 1024 * 1024;
>> For platforms that might have limited carve out (ST, CZ, RV), we may
>> want to do something like:
>> if (adev->gmc.real_vram_size <= 32MB) // 128MB?
>>      stolen_size = 256K;
> That means artifacts are likely to still occur during initialization on
> systems where we only reserve 256K, right?
>
>
> I wonder if there's no way to determine which part of VRAM is being
> scanned out. If there was, we could just create a normal BO covering
> that, which would get destroyed once no CRTC references it anymore.

Unfortunately it goes further than that. The stolen VRAM is needed for 
VGA emulation, not only for scanout.

But yes I agree that we somehow figure that value out from the BIOS. If 
I'm not completely mistaken I've also seen some atombios table with that 
info in some discussion.

Christian.