Re: [PATCH 1/2] drm/amdgpu: read FB through BAR0 when aperture is unavailable

["Christian König" <ckoenig.leichtzumerken@gmail.com>]

On 7/1/26 07:53, chong li wrote:
> Allow early VRAM reads to fall back to a temporary BAR0 mapping
> when the normal aperture mapping has not been established yet.

Clear NAK.

You are just trying to fix a symptom of incorrect initialization order here.

Regards,
Christian.

> 
> Signed-off-by: chong li <chongli2@amd.com>
> Co-authored-by: Cursor <cursoragent@cursor.com>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 43 +++++++++++++++++++++-
>  1 file changed, 42 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
> index 5442a1fc1c37..610d82b79de3 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
> @@ -743,6 +743,44 @@ void amdgpu_device_mm_access(struct amdgpu_device *adev, loff_t pos,
>  	drm_dev_exit(idx);
>  }
>  
> +static int amdgpu_device_read_fb_via_bar0(struct amdgpu_device *adev,
> +					  u64 offset, void *buf, size_t size)
> +{
> +	resource_size_t bar_start, bar_size, map_base;
> +	void __iomem *vram;
> +	size_t map_offset, map_size;
> +	unsigned long flags;
> +	u64 end;
> +
> +	if (!buf || !size)
> +		return -EINVAL;
> +
> +	flags = pci_resource_flags(adev->pdev, 0);
> +	if ((flags & IORESOURCE_UNSET) || !(flags & IORESOURCE_MEM))
> +		return -EINVAL;
> +
> +	bar_size = pci_resource_len(adev->pdev, 0);
> +	if (!bar_size)
> +		return -ENODEV;
> +
> +	if (check_add_overflow(offset, size, &end) || end > bar_size)
> +		return -EINVAL;
> +
> +	bar_start = pci_resource_start(adev->pdev, 0);
> +	map_offset = offset_in_page(offset);
> +	map_base = bar_start + (offset & PAGE_MASK);
> +	map_size = PAGE_ALIGN(map_offset + size);
> +
> +	vram = ioremap_wc(map_base, map_size);
> +	if (!vram)
> +		return -ENOMEM;
> +
> +	memcpy_fromio(buf, (u8 __iomem *)vram + map_offset, size);
> +	iounmap(vram);
> +
> +	return 0;
> +}
> +
>  /**
>   * amdgpu_device_aper_access - access vram by vram aperture
>   *
> @@ -762,8 +800,11 @@ size_t amdgpu_device_aper_access(struct amdgpu_device *adev, loff_t pos,
>  	size_t count = 0;
>  	uint64_t last;
>  
> -	if (!adev->mman.aper_base_kaddr)
> +	if (!adev->mman.aper_base_kaddr) {
> +		if (!write && !amdgpu_device_read_fb_via_bar0(adev, pos, buf, size))
> +			return size;
>  		return 0;
> +	}
>  
>  	last = min(pos + size, adev->gmc.visible_vram_size);
>  	if (last > pos) {