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

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

Hi Christian,

On 1/5/2024 9:39 PM, Christian König 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.
> 
Do you mean MSI-X? There are no extended capability registers related with
MSI or MSI-x.

How about reading the 0x100 register in the extended config space since the
extended capabilities always start from the offset 0x100 according the pcie
spec.

> 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.

I think the MSI related configuration registers are in the legacy
configuration space. So the system don't need to use mmio to access these
registers.

Regards,
Ma Jun

> 
> 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;
>