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

[Karol Herbst]

On Fri, Aug 19, 2022 at 6:00 PM Limonciello, Mario
<mario.limonciello@xxxxxxx> wrote:
>
> On 8/19/2022 10:44, Karol Herbst wrote:
> > On Fri, Aug 19, 2022 at 4:25 PM Mario Limonciello
> > <mario.limonciello@xxxxxxx> 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.
>
> My apologies, I was certainly part of the impetus for this W/A in the
> first place while I was at my previous employer.  Your comment
> re-affirms to me that at least the first patch is correct.
>

Yeah, no worries. I just hope that people in the future will
communicate such things.

Anyway, there are a few issues with the runpm stuff left, and looking
at what nvidia does in their open driver makes me wonder if we might
need a bigger overhaul of runpm. They do apply bridge/host controller
specific workarounds and I suspect some of them are related here as
the workaround I came up with in nouveau can be seen in 434fdb51513bf.

But also having access to documentation/specification from what Nvidia
is doing would be quite helpful. We know that on some really new AMD
systems we run into new issues and this needs some investigation. I
simply don't access to any laptops where this problem can be seen.

> >
> > 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.
> >
>
> If the other two really aren't needed anymore, then yeah we should just
> tear all 3 out.  If that's the direction we go, I would appreciate some
> commit IDs to reference in the commit message for tearing them out so
> that if they end up backporting to stable we know how far they should go.
>