[PATCH 1/1] drm/amdgpu: return early on error while setting bar0 memtype

[Lazar, Lijo]

On 11/2/2021 4:39 PM, Christian König wrote:
> Am 02.11.21 um 11:11 schrieb Das, Nirmoy:
>>
>> On 11/2/2021 9:00 AM, Lazar, Lijo wrote:
>>>
>>>
>>> On 10/29/2021 8:39 PM, Nirmoy Das wrote:
>>>> We set WC memtype for aper_base but don't check return value
>>>> of arch_io_reserve_memtype_wc(). Be more defensive and return
>>>> early on error.
>>>>
>>>> Signed-off-by: Nirmoy Das <nirmoy.das at amd.com>
>>>> ---
>>>>   drivers/gpu/drm/amd/amdgpu/amdgpu_object.c | 7 ++++++-
>>>>   1 file changed, 6 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c 
>>>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
>>>> index 073ba2af0b9c..6b25982a9077 100644
>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
>>>> @@ -1032,9 +1032,14 @@ int amdgpu_bo_init(struct amdgpu_device *adev)
>>>>       /* On A+A platform, VRAM can be mapped as WB */
>>>>       if (!adev->gmc.xgmi.connected_to_cpu) {
>>>>           /* reserve PAT memory space to WC for VRAM */
>>>> -        arch_io_reserve_memtype_wc(adev->gmc.aper_base,
>>>> +        int r = arch_io_reserve_memtype_wc(adev->gmc.aper_base,
>>>>                   adev->gmc.aper_size);
>>>
>>> BTW, isn't it more appropriate to use visible vram size? There are 
>>> cases where pci resize rounds aperture to the next higher size > size 
>>> of actual VRAM.
>>
>>
>> Good point, I will update this one and send again.
> 
> Not a good idea at all.
> 
> The aperture size is rounded up to the next power of two and that's 
> exactly what we should stick to if we don't want to get an error code in 
> return.
> 
PCI rebar sizes have its restrictions. It jumps from 4G to 8G to 16G and 
so on. Why we need to map 16G for a card with 12G VRAM? BTW, how it 
increases the failure chance - this mapping happens in page sizes, right?

Thanks,
Lijo

> Regards,
> Christian.
> 
>>
>>
>> Regards,
>>
>> Nirmoy
>>
>>
>>>
>>> Thanks,
>>> Lijo
>>>>   +        if (r) {
>>>> +            DRM_ERROR("Unable to set WC memtype for the aperture 
>>>> base\n");
>>>> +            return r;
>>>> +        }
>>>> +
>>>>           /* Add an MTRR for the VRAM */
>>>>           adev->gmc.vram_mtrr = arch_phys_wc_add(adev->gmc.aper_base,
>>>>                   adev->gmc.aper_size);
>>>>
>