Re: [PATCH v3 0/2] efi/x86: Call set_os() protocol on dual GPU Macs

[Aditya Garg]

> On 25 Jul 2024, at 6:12 PM, Ard Biesheuvel <ardb@xxxxxxxxxx> wrote:
> 
> On Wed, 24 Jul 2024 at 18:31, Lukas Wunner <lukas@xxxxxxxxx> wrote:
>> 
>> On Wed, Jul 24, 2024 at 04:26:58PM +0000, Aditya Garg wrote:
>>>>> On 24 Jul 2024, at 9:31 PM, Lukas Wunner <lukas@xxxxxxxxx> wrote:
>>>>> I note that on x86, the efistub walks over all PCI devices in the system
>>>>> (see setup_efi_pci() in drivers/firmware/efi/libstub/x86-stub.c) and
>>>>> retrieves the Device ID and Vendor ID.  We could additionally retrieve
>>>>> the Class Code and count the number of GPUs in the system by checking
>>>>> whether the Class Code matches PCI_BASE_CLASS_DISPLAY.  If there's
>>>>> at least 2 GPUs in the system, invoke apple_set_os.
>>> 
>>> This also looks like a good idea, but I'm not well aware of the pci
>>> quirks in the Linux kernel. So, would consider it a bug report for
>>> the maintainers to fix.
>> 
>> This is not a PCI quirk in the kernel.  The efistub is a separate
>> program.  I'm saying that the efistub already walks over all PCI devices,
>> it would be trivial to hook into this to count GPUs, recognize the T2
>> device or do something else entirely.
>> 
> 
> Thanks for the analysis, and for the suggestions.
> 
> I wouldn't object to changes to the EFI stub that implement something
> along these lines, although I'd like to understand a bit better what
> the actual issue is.
> 
> If PCI resource allocation is the culprit here, wouldn't it be better
> to force Linux to reallocate those from scratch? IIRC there is already
> a command line option for this.

I guess you are talking about 'pci=realloc'. Adding this doesn't fix the issue.