On Wed, Jul 8, 2026 at 1:59 PM Mario Limonciello <[email protected]> wrote: > > > > On 7/8/26 12:52, Oz Tiram wrote: > > Hi Mario, > > > > Tested on 7.2-rc2 with your patch applied. The mismatch condition is > > unchanged from 6.18.35: > > > > amdgpu 0000:0b:00.0: VFCT bus number mismatch: table 106 != runtime 11, > > matching by device identity (vendor 0x1002 device 0x1900) > > amdgpu 0000:0b:00.0: Fetched VBIOS from VFCT > > > > Both GPUs initialise fully with your patch. > > > > I also tested 7.2-rc2 without pci=realloc,assign-busses to check whether > > the pci/realloc changes fixed the dGPU probe failure. They did not -- the > > dGPU still fails on 7.2-rc2: > > > > amdgpu 0000:03:00.0: Fatal error during GPU init > > amdgpu 0000:03:00.0: probe with driver amdgpu failed with error -12 > > > > Without the kernel argument the iGPU sits at its POST bus (0x6A), VFCT > > matches directly, and it works fine -- but the dGPU is unusable. > > pci=realloc,assign-busses remains necessary for this machine on 7.2-rc2, > > which means the VFCT mismatch persists and your patch is still needed. > > > > Thank you for not giving up on me so quickly! > > This is my first time working on such issue. It feels > > daunting to modify kernel code. > > OK, in that case I will clean up and post the patches shortly. You'll > be able to use them for a workaround if everyone else is aligned. The > part I'm worried about with these is how they would interplay with a > system with multiple of the same GPU. But I don't believe we would be > fetching VBIOS from VFCT in that case most likely? Not sure.
It's allowed by the spec. A number of apple systems use VFCT for multu-GPU systems with the same GPU. Alex > > We really shouldn't have to set pci=realloc,assign-busses on a design > with all internal PCIe devices. We should adjust resource allocation > code for this case. > > So please start another another thread with the linux-pci mailing list > on this issue, include a full dmesg showing what happens when you don't > add the parameters and then what happens when you do (feel free to > include/reference this patch in that thread too). > > If you want to use one, this is the kind of thing an LLM with access to > a kernel checkout and both those dmesgs might be good at helping to > propose a draft for a solution to the resource allocation code too. > > You can CC me on that linux-pci mailing list submission, and we'll see > if we can come up with a better solution for you. > > > > > Oz > > > > > > On 7/8/26 18:39, Mario Limonciello wrote: > >> On 7/8/26 11:35, Oz Tiram wrote: > >>> Hi Mario, > >>> > >>> The GPU is internal. It's an AMD RADEON PRO W7800 48GB. > >>> The kernel is built from gentoo-sources-6.18.35. > >>> > >>> I will test the latest sys-kernel/vanilla-sources (7.1.3) and let you > >>> know. > >>> > >>> Best regards, > >> > >> Thanks. Can you please test 7.2-rc2? > >> > >> I'll clean up the workaround and propose it for review in parallel. > >> > >>> > >>> Oz > >>> > >>> On 7/8/26 15:13, Mario Limonciello wrote: > >>>> > >>>> On 7/8/26 08:10, Oz Tiram wrote: > >>>>> Hi Mario, > >>>>> > >>>>> > If you drop that - does this notice still come up? > >>>>> > >>>>> No, the notice does not appear without pci=realloc,assign-busses. > >>>>> The iGPU stays at its POST bus (0x6A = 106), VFCT matches > >>>>> directly, and it fetches the VBIOS without any mismatch. > >>>>> > >>>>> However, dropping the kernel argument is not an option on this > >>>>> machine: > >>>>> without it the discrete GPU (0x7449) fails to probe entirely: > >>>>> > >>>>> amdgpu 0000:03:00.0: amdgpu: Fatal error during GPU init > >>>>> amdgpu 0000:03:00.0: probe with driver amdgpu failed with error -12 > >>>>> > >>>>> The firmware BARs cannot be mapped without resource reallocation, so > >>>>> pci=realloc,assign-busses is required for the dGPU, which in turn > >>>>> reassigns > >>>>> the iGPU to bus 0x0B and triggers the mismatch your patch resolves. > >>>> > >>>> Got it; thanks for clarifying. I would like to dig a little bit > >>>> futher into that though. What kernel are you finding this behavior > >>>> and can it still reproduce with 7.2-rc2 if it's older? There was a > >>>> bunch of pci/realloc changes that happened in the last cycle that > >>>> might have helped this. > >>>> > >>>> Also; is it an eGPU (external) or dGPU (internal)? > >>>> > >>>> If it's an dGPU IMO this is arguably a BIOS issue that not enough > >>>> resources were applied in the first place. > >>>> > >>>> Thanks, > >>>> > >>>>> > >>>>> > >>>>> Thank you, > >>>>> > >>>>> Oz > >>>>> > >>>>> > >>>>> On 7/8/26 14:55, Mario Limonciello wrote: > >>>>>> Hi Oz, > >>>>>> > >>>>>> On 7/8/26 07:36, Oz Tiram wrote: > >>>>>>> Hi Mario, > >>>>>>> > >>>>>>> Tested on a Morefine MNAS X1 AI Workstation (AMD Ryzen 7 Pro > >>>>>>> 8845HS / Radeon 780M iGPU) with pci=realloc,assign-busses. > >>>>>>> > >>>>>>> The VFCT entry for the iGPU has PCIBus=106 (0x6A, recorded at > >>>>>>> POST) while the > >>>>>>> runtime bus is 11 (0x0B). Your patch fires exactly as expected: > >>>>>>> > >>>>>>> amdgpu 0000:0b:00.0: amdgpu: VFCT bus number mismatch: table > >>>>>>> 106 ! = runtime 11, > >>>>>>> matching by device identity (vendor 0x1002 device 0x1900) > >>>>>>> amdgpu 0000:0b:00.0: amdgpu: Fetched VBIOS from VFCT > >>>>>>> > >>>>>>> The iGPU initialises fully and drives the framebuffer. > >>>>>>> > >>>>>>> One minor nit: the dev_notice format string ends with \\n (two > >>>>>>> characters) rather > >>>>>>> than \n. The resulting kernel message has a literal "\n" at the > >>>>>>> end. Same issue > >>>>>>> exists in the nearby "too short #2" dev_info -- not introduced by > >>>>>>> your patch, but > >>>>>>> might be worth cleaning up. > >>>>>>> > >>>>>>> Tested-by: Oz Tiram <[email protected]> > >>>>>>> > >>>>>> > >>>>>> Thanks for confirming. Before I split up this patch and post it > >>>>>> in smaller logical pieces can you confirm my proposed root cause > >>>>>> is right that this issue happens because "pci=realloc,assign- > >>>>>> busses" was on your kernel command line? > >>>>>> > >>>>>> If you drop that - does this notice still come up? > >>>>>> > >>>>>> Thanks, > >>>>>> > >>>>>>> On 7/6/26 02:56, Mario Limonciello wrote: > >>>>>>>> > >>>>>>>> > >>>>>>>> On 7/5/26 14:10, Oz Tiram wrote: > >>>>>>>>> Hi Mario, > >>>>>>>>> > >>>>>>>>> To make sure I understand correctly: are you suggesting that > >>>>>>>>> the bus > >>>>>>>>> number in the VFCT was legitimate at BIOS POST time, and that > >>>>>>>>> pci=realloc,assign-busses is what changes it at runtime, > >>>>>>>>> causing the > >>>>>>>>> mismatch? > >>>>>>>> > >>>>>>>> That's what it sounds like right now. You can easily drop all > >>>>>>>> the superfluous kernel command line optiosn and see. > >>>>>>>> > >>>>>>>>> > >>>>>>>>> I'm not familiar enough with the PCI subsystem to know the > >>>>>>>>> right way to > >>>>>>>>> implement that — could you point me in the right direction? > >>>>>>>> > >>>>>>>> Well there's a variety of ways to do it. But how about we start > >>>>>>>> here - if we make that specific busnr match optional and instead > >>>>>>>> make a VID/DID match. > >>>>>>>> > >>>>>>>> See if the attached patch helps. > >>>>>>>> > >>>>>>>>> > >>>>>>>>> Oz > >>>>>>>>> > >>>>>>>>> On 7/5/26 20:37, Mario Limonciello wrote: > >>>>>>>>>> > >>>>>>>>>> > >>>>>>>>>> On 7/5/26 05:04, 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. The specific case motivating > >>>>>>>>>>> this patch > >>>>>>>>>>> is a hybrid graphics machine (dGPU + APU) where: > >>>>>>>>>>> > >>>>>>>>>>> - The VFCT table contains the iGPU entry but with a stale > >>>>>>>>>>> PCIBus value > >>>>>>>>>>> from BIOS POST time (0x6A). When the kernel boots with > >>>>>>>>>>> pci=realloc,assign-busses, PCI bus numbers are > >>>>>>>>>>> reassigned dynamically > >>>>>>>>>>> and the iGPU lands on bus 0x0B at runtime. > >>>>>>>>>>> amdgpu_acpi_vfct_bios() > >>>>>>>>>>> matches entries by bus number, so the entry is never found. > >>>>>>>>>>> - The VRAM BAR is unmapped at probe time. > >>>>>>>>>>> - The ROM BAR is zero (PCI firmware did not assign it). > >>>>>>>>>>> - No platform BIOS mapping exists. > >>>>>>>>>>> > >>>>>>>>>>> The UEFI GOP driver initialises the iGPU successfully for > >>>>>>>>>>> early display, > >>>>>>>>>>> confirming the hardware is functional. The VBIOS image data > >>>>>>>>>>> embedded in > >>>>>>>>>>> the VFCT is also valid; only the PCIBus metadata is wrong. > >>>>>>>>>> > >>>>>>>>>> So the BIOS on this machine is actually totally fine; it's > >>>>>>>>>> just when the kernel is booted to reassign busses there is a > >>>>>>>>>> problem? > >>>>>>>>>> > >>>>>>>>>> In that case; why not detect the kernel was booted this way > >>>>>>>>>> and keep track of the original bus number when reassigned to > >>>>>>>>>> avoid the issue? > >>>>>>>>>> > >>>>>>>>>>> The firmware > >>>>>>>>>>> file can be extracted directly from the VFCT using dd: > >>>>>>>>>>> > >>>>>>>>>>> dd if=/sys/firmware/acpi/tables/VFCT bs=1 skip=$((0x68)) > >>>>>>>>>>> count=16896 \ > >>>>>>>>>>> of=/lib/firmware/amdgpu/1002_1900.bin > >>>>>>>>>>> > >>>>>>>>>>> (0x68 is the byte offset of the VBIOS image after the ACPI > >>>>>>>>>>> table header > >>>>>>>>>>> and VFCT_IMAGE_HEADER; the image length 16896 comes from the > >>>>>>>>>>> ImageLength > >>>>>>>>>>> field in VFCT_IMAGE_HEADER.) > >>>>>>>>>>> > >>>>>>>>>>> The driver then prints "Unable to locate a BIOS ROM" and > >>>>>>>>>>> refuses to > >>>>>>>>>>> bind, leaving the APU completely unusable under Linux. > >>>>>>>>>>> > >>>>>>>>>>> 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 as > >>>>>>>>>>> above to be > >>>>>>>>>>> placed in /lib/firmware/ and makes the binding succeed > >>>>>>>>>>> without patching > >>>>>>>>>>> ACPI tables or BIOS. > >>>>>>>>>>> > >>>>>>>>>>> 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. > >>>>>>>>>> > >>>>>>>>>> What happens if the VBIOS changes in another way one boot to > >>>>>>>>>> another? You might have some other stateful information that > >>>>>>>>>> isn't updated. > >>>>>>>>>> > >>>>>>>>>> The whole thing to me feels like a hack for a behavior we can > >>>>>>>>>> control in the kernel when doing reassignments. > >>>>>>>>>>> > >>>>>>>>>>> Signed-off-by: Oz Tiram <[email protected]> > >>>>>>>>>>> --- > >>>>>>>>>>> v2: Fix commit message: clarify that VFCT contains the iGPU > >>>>>>>>>>> entry but > >>>>>>>>>>> with a stale PCIBus from BIOS POST that mismatches the > >>>>>>>>>>> runtime bus > >>>>>>>>>>> number assigned by pci=realloc,assign-busses. Explain > >>>>>>>>>>> that the VBIOS > >>>>>>>>>>> image data is valid and document the dd extraction > >>>>>>>>>>> command and byte > >>>>>>>>>>> offsets. Note that the UEFI GOP driver initialises the > >>>>>>>>>>> iGPU > >>>>>>>>>>> successfully, confirming the hardware is functional. > >>>>>>>>>>> > >>>>>>>>>>> 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; > >>>>>>>>>> > >>>>>> > >>>> > >> >
