Re: [RFC 0/2] Stop the abuse of Linux-* _OSI strings

From: Lyude Paul <lyude@redhat.com>
To: Karol Herbst <kherbst@redhat.com>,
	Mario Limonciello <mario.limonciello@amd.com>
Cc: linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org,
	rafael@kernel.org, Len Brown <lenb@kernel.org>,
	nouveau@lists.freedesktop.org, hdegoede@redhat.com,
	ddadap@nvidia.com, kai.heng.feng@canonical.com,
	Dell.Client.Kernel@dell.com
Subject: Re: [RFC 0/2] Stop the abuse of Linux-* _OSI strings
Date: Mon, 22 Aug 2022 17:18:28 -0400	[thread overview]
Message-ID: <c10b243a7be185ba119bdfce9a46e609db3bdd3b.camel@redhat.com> (raw)
In-Reply-To: <CACO55tuw_2QWFMr0t6-JfUiQ4M7V3ZMKC7jHYTyERypaU3TekQ@mail.gmail.com>

On Fri, 2022-08-19 at 17:44 +0200, Karol Herbst wrote:
> On Fri, Aug 19, 2022 at 4:25 PM Mario Limonciello
> <mario.limonciello@amd.com> wrote:
> > 
> > 3 _OSI strings were introduced in recent years that were intended
> > to workaround very specific problems found on specific systems.
> > 
> > The idea was supposed to be that these quirks were only used on
> > those systems, but this proved to be a bad assumption.  I've found
> > at least one system in the wild where the vendor using the _OSI
> > string doesn't match the _OSI string and the neither does the use.
> > 
> > So this brings a good time to review keeping those strings in the kernel.
> > There are 3 strings that were introduced:
> > 
> > Linux-Dell-Video
> > -> Intended for systems with NVIDIA cards that didn't support RTD3
> > Linux-Lenovo-NV-HDMI-Audio
> > -> Intended for powering on NVIDIA HDMI device
> > Linux-HPI-Hybrid-Graphics
> > -> Intended for changing dGPU output
> > 
> > AFAIK the first string is no longer relevant as nouveau now supports
> > RTD3.  If that's wrong, this can be changed for the series.
> > 
> 
> Nouveau always supported RTD3, because that's mainly a kernel feature.
> When those were introduced we simply had a bug only hit on a few
> systems. And instead of helping us to debug this, this workaround was
> added :( We were not even asked about this.
> 
> I am a bit curious about the other two though as I am not even sure
> they are needed at all as we put other work arounds in place. @Lyude
> Paul might know more about these.

Some of the _OSI strings are totally fine. From my recollection:

[    0.242993] ACPI: Added _OSI(Linux-Lenovo-NV-HDMI-Audio)
^ this one is needed to do a couple of ACPI tricks at startup to get the PCIe
device for audio on nvidia's GPU to be detected properly

[    0.242993] ACPI: Added _OSI(Linux-HPI-Hybrid-Graphics)

I don't actually know how necessary this is, but I'm hesistant to call this
one bad as it may be related to the funny mux configurations that I'm learning
may exist on HP machines.

> 

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat