Re: [PATCH] drm/amd/amdgpu: add firmware file fallback for APU VBIOS discovery

[Mario Limonciello <mario.limonciello@amd.com>]

On 6/21/26 13:01, Oz Tiram wrote:
> APUs (e.g. AMD Radeon 780M / HawkPoint, PCI 1002:1900) have no
> dedicated VBIOS ROM chip.  amdgpu_get_bios_apu() attempts four paths
> before giving up:
> 
>    1. ACPI VFCT table
>    2. VRAM BAR read
>    3. ROM BAR read
>    4. platform BIOS
> 
> On some systems all four fail:

That's pretty odd to me.  Isn't this a BIOS bug?  Can you share more 
about why all of these are failing?

Does the UEFI GOP driver work?

> 
>    - The VFCT table is absent or contains only the discrete GPU entry
>      (e.g. when a custom ACPI override is present for the dGPU only).
>    - The VRAM BAR is unmapped at probe time.
>    - The ROM BAR is zero (PCI firmware did not assign it; observed even
>      with pci=realloc,assign-busses).
>    - No platform BIOS mapping exists.
> 
> The driver then prints "Unable to locate a BIOS ROM" and refuses to
> bind, leaving the APU completely unusable under Linux even though the
> hardware is functional.
> 
> Add a fifth fallback: request a firmware file named
> "amdgpu/<vendor>_<device>.bin" (e.g. "amdgpu/1002_1900.bin") via
> request_firmware().  This allows a VBIOS image extracted from the
> running hardware 

I thought you just said this didn't work.  How did you extract it?

> to be shipped as a firmware blob in /lib/firmware/ and
> makes the binding succeed without any change to the ACPI tables.
> 
> The fallback is only reached if all existing paths have already failed,
> so there is no regression risk for boards where VFCT or ROM BAR work.
> 
> Signed-off-by: Oz Tiram <oz@shift-computing.de>
> ---
> v2: Validate the fetched firmware with check_atom_bios() before accepting
>      it, consistent with all other VBIOS discovery paths.  Save fw->size
>      before release_firmware() so it remains valid for the size check.
>      Release the buffer via amdgpu_bios_release() if validation fails.
> 
>   drivers/gpu/drm/amd/amdgpu/amdgpu_bios.c | 23 +++++++++++++++++++++++
>   1 file changed, 23 insertions(+)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_bios.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_bios.c
> index aa039e148a5e..86064c753b09 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_bios.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_bios.c
> @@ -26,6 +26,7 @@
>    *          Jerome Glisse
>    */
>   
> +#include <linux/firmware.h>
>   #include "amdgpu.h"
>   #include "atom.h"
>   
> @@ -457,6 +458,28 @@ static bool amdgpu_get_bios_apu(struct amdgpu_device *adev)
>   		goto success;
>   	}
>   
> +	{
> +		const struct firmware *fw;
> +		char fw_name[32];
> +		size_t fw_size;
> +
> +		snprintf(fw_name, sizeof(fw_name), "amdgpu/%04x_%04x.bin",
> +			 adev->pdev->vendor, adev->pdev->device);
> +		if (request_firmware(&fw, fw_name, adev->dev) == 0) {
> +			adev->bios = kmemdup(fw->data, fw->size, GFP_KERNEL);
> +			fw_size = fw->size;
> +			release_firmware(fw);
> +			if (!adev->bios || !check_atom_bios(adev, fw_size)) {
> +				amdgpu_bios_release(adev);
> +			} else {
> +				adev->bios_size = fw_size;
> +				dev_info(adev->dev, "Fetched VBIOS from firmware file %s\n",
> +					 fw_name);
> +				goto success;
> +			}
> +		}
> +	}
> +
>   	dev_err(adev->dev, "Unable to locate a BIOS ROM\n");
>   	return false;
>