linux-kernel - Re: [PATCH] x86/efistub: Add options for forcing Apple set

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Message-ID:
 <PN0PR01MB960815D7115B2DE62E27DCC4B8FD2@PN0PR01MB9608.INDPRD01.PROD.OUTLOOK.COM>
Date: Tue, 11 Feb 2025 05:45:30 +0000
From: Aditya Garg <gargaditya08@...e.com>
To: Lukas Wunner <lukas@...ner.de>
CC: Lleyton Gray <lleyton@...alabs.com>, Ard Biesheuvel <ardb@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>
Subject: Re: [PATCH] x86/efistub: Add options for forcing Apple set_os
 protocol



> On 11 Feb 2025, at 1:39 AM, Lukas Wunner <lukas@...ner.de> wrote:
> 
> On Wed, Jan 01, 2025 at 11:39:13AM +0000, Aditya Garg wrote:
>> We have had issues with other people unable to use their eGPU if their
>> Mac doesn't have the apple set os quirk. We probably could do dual VGA
>> checks suggested by Lukas, but will it work with GPU hotplug?
> 
> About hotplug:  There is a tiny time window when the EFI stub runs
> during which an eGPU may be hotplugged and incorrectly not be
> detected.  I.e. the quirk is not applied.  I don't think this can
> be fixed.
> 
> If an eGPU is hotplugged while EFI boot services are still running,
> Apple's EFI Thunderbolt driver will set up a tunnel to the device
> and it will then be visible to the kernel's efi stub.  E.g. if you
> hold down the Option key during boot and attach an eGPU, then
> select the operating system to boot, the eGPU should correctly be
> seen by the efi stub and the quirk is applied.
> 
> However hotplugging an eGPU at exactly the moment when the efi stub
> runs results in a race between the efi stub doing all the initialization
> and exiting boot services on the one hand, and the EFI Thunderbolt
> driver bringing up the eGPU on the other hand.
> 
> But IMO this is "good enough".

Something is better than nothing.

I'll test your patch, and imo restricting it to Apple devices should be a good idea.
> 
> Thanks,
> 
> Lukas