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From:   Kai-Heng Feng <kai.heng.feng@canonical.com>
Date:   Tue, 23 Aug 2022 11:47:50 +0800
Message-ID: <CAAd53p6dTdWzkiyH6Sz=YubhdibvGa4hZ+EPN7mZA4aYSPd_6g@mail.gmail.com>
Subject: Re: [RFC 0/2] Stop the abuse of Linux-* _OSI strings
To:     Lyude Paul <lyude@redhat.com>
Cc:     Karol Herbst <kherbst@redhat.com>,
        Mario Limonciello <mario.limonciello@amd.com>,
        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, Dell.Client.Kernel@dell.com,
        Aaron Ma <aaron.ma@canonical.com>
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[+Cc Aaron]

On Tue, Aug 23, 2022 at 5:18 AM Lyude Paul <lyude@redhat.com> wrote:
>
> 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

This should be fixed by commit b516ea586d71 ("PCI: Enable NVIDIA HDA
controllers").
Aaron worked on more Lenovo systems than me, so he may be more sure of it.

>
> [    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.

Should be fixed by commit 8e55f99c510f ("drm/i915: Invoke another _DSM
to enable MUX on HP Workstation laptops").

And for "Linux-Dell-Video", it should be fixed by 5775b843a619 ("PCI:
Restore config space on runtime resume despite being unbound").

So actually I am in favor of removing them all.

Kai-Heng

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