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

[Oz Tiram]

Hi Mario,

Sorry for the slow response, I'm new to the kernel contribution process. 
Thanks for the review. v2 addresses your questions: -

The VFCT does contain the iGPU entry, but with a stale PCIBus value from 
BIOS POST time (0x6A). With pci=realloc,assign-busses the iGPU lands on 
bus 0x0B at runtime, so amdgpu_acpi_vfct_bios() never matches it

This is clarified in the commit message along with a note that the UEFI 
GOP driver initializes the iGPU successfully, confirming the hardware is 
functional.

The VBIOS image data in the VFCT is valid — only the PCIBus metadata is 
wrong.

The firmware file was extracted directly from the VFCT with dd, skipping 
past the ACPI header and VFCT_IMAGE_HEADER. The commit message now 
documents the exact command and byte offsets.

The patch follows.

Oz

On 6/26/26 19:42, Mario Limonciello wrote:


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 <o...@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;