Re: [PATCH] drm/amdgpu: Check resize bar register when system uses large bar

["Ma, Jun" <majun@amd.com>]

Hi Alex,

On 1/6/2024 12:11 AM, Alex Deucher wrote:
> On Fri, Jan 5, 2024 at 9:16 AM Christian König
> <ckoenig.leichtzumerken@gmail.com> wrote:
>>
>> Am 21.12.23 um 02:58 schrieb Ma, Jun:
>>> Hi Christian,
>>>
>>>
>>> On 12/20/2023 10:10 PM, Christian König wrote:
>>>> Am 19.12.23 um 06:58 schrieb Ma Jun:
>>>>> Print a warnning message if the system can't access
>>>>> the resize bar register when using large bar.
>>>> Well pretty clear NAK, we have embedded use cases where this would
>>>> trigger an incorrect warning.
>>>>
>>>> What should that be good for in the first place?
>>>>
>>> Some customer platforms do not enable mmconfig for various reasons, such as
>>> bios bug, and therefore cannot access the GPU extend configuration
>>> space through mmio.
>>>
>>> Therefore, when the system enters the d3cold state and resumes,
>>> the amdgpu driver fails to resume because the extend configuration
>>> space registers of GPU can't be restored. At this point, Usually we
>>> only see some failure dmesg log printed by amdgpu driver, it is
>>> difficult to find the root cause.
>>>
>>> So I thought it would be helpful to print some warning messages at
>>> the beginning to identify problems quickly.
>>
>> Interesting bug, but we can't do this here. We have a couple of devices
>> where the REBAR cap isn't enabled for some reason (or not correctly
>> enabled).
>>
>> In this case this would print a warning even when there isn't anything
>> wrong.
>>
>> What we could potentially do is to check for the MSI extension, that
>> should always be there if I'm not completely mistaken.
>>
>> But how does this hardware platform even works without the extended mmio
>> space? I mean we can't even enable/disable MSI in that configuration if
>> I'm not completely mistaken.
> 
> That system is probably similar to what Mario mentioned:
> https://lore.kernel.org/linux-pci/20231215220343.22523-1-mario.limonciello@amd.com/
> 
Yes, It's the same problem.

Regards,
Ma Jun


> Alex
> 
>>
>> Regards,
>> Christian.
>>
>>>
>>> Regards,
>>> Ma Jun
>>>
>>>> Regards,
>>>> Christian.
>>>>
>>>>> Signed-off-by: Ma Jun <Jun.Ma2@amd.com>
>>>>> ---
>>>>>    drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 10 +++++++++-
>>>>>    1 file changed, 9 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
>>>>> index 4b694696930e..e7aedb4bd66e 100644
>>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
>>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
>>>>> @@ -1417,6 +1417,12 @@ void amdgpu_device_wb_free(struct amdgpu_device *adev, u32 wb)
>>>>>             __clear_bit(wb, adev->wb.used);
>>>>>    }
>>>>>
>>>>> +static inline void amdgpu_find_rb_register(struct amdgpu_device *adev)
>>>>> +{
>>>>> +   if (!pci_find_ext_capability(adev->pdev, PCI_EXT_CAP_ID_REBAR))
>>>>> +           DRM_WARN("System can't access the resize bar register,please check!!\n");
>>>>> +}
>>>>> +
>>>>>    /**
>>>>>     * amdgpu_device_resize_fb_bar - try to resize FB BAR
>>>>>     *
>>>>> @@ -1444,8 +1450,10 @@ int amdgpu_device_resize_fb_bar(struct amdgpu_device *adev)
>>>>>
>>>>>     /* skip if the bios has already enabled large BAR */
>>>>>     if (adev->gmc.real_vram_size &&
>>>>> -       (pci_resource_len(adev->pdev, 0) >= adev->gmc.real_vram_size))
>>>>> +       (pci_resource_len(adev->pdev, 0) >= adev->gmc.real_vram_size)) {
>>>>> +           amdgpu_find_rb_register(adev);
>>>>>             return 0;
>>>>> +   }
>>>>>
>>>>>     /* Check if the root BUS has 64bit memory resources */
>>>>>     root = adev->pdev->bus;
>>