Re: [Nouveau] [PATCH 1/7] Revert "ACPI / OSI: Add OEM _OSI string to enable dGPU direct output"

[Alex Deucher <alexdeucher@gmail.com>]

On Thu, Aug 15, 2019 at 10:30 AM <Mario.Limonciello@dell.com> wrote:
>
> > On Thu, Aug 15, 2019 at 10:15 AM Karol Herbst <kherbst@redhat.com> wrote:
> > >
> > > On Thu, Aug 15, 2019 at 4:13 PM Alex Deucher <alexdeucher@gmail.com>
> > wrote:
> > > >
> > > > On Thu, Aug 15, 2019 at 10:04 AM Karol Herbst <kherbst@redhat.com> wrote:
> > > > >
> > > > > On Thu, Aug 15, 2019 at 3:56 PM <Mario.Limonciello@dell.com> wrote:
> > > > > >
> > > > > > > -----Original Message-----
> > > > > > > From: linux-acpi-owner@vger.kernel.org <linux-acpi-
> > owner@vger.kernel.org> On
> > > > > > > Behalf Of Dave Airlie
> > > > > > > Sent: Wednesday, August 14, 2019 5:48 PM
> > > > > > > To: Karol Herbst
> > > > > > > Cc: LKML; Linux ACPI; dri-devel; nouveau; Rafael J . Wysocki; Alex Hung;
> > Ben
> > > > > > > Skeggs; Dave Airlie
> > > > > > > Subject: Re: [Nouveau] [PATCH 1/7] Revert "ACPI / OSI: Add OEM _OSI
> > string to
> > > > > > > enable dGPU direct output"
> > > > > > >
> > > > > > > On Thu, 15 Aug 2019 at 07:31, Karol Herbst <kherbst@redhat.com>
> > wrote:
> > > > > > > >
> > > > > > > > This reverts commit 28586a51eea666d5531bcaef2f68e4abbd87242c.
> > > > > > > >
> > > > > > > > The original commit message didn't even make sense. AMD _does_
> > support it and
> > > > > > > > it works with Nouveau as well.
> > > > > > > >
> > > > > > > > Also what was the issue being solved here? No references to any bugs
> > and not
> > > > > > > > even explaining any issue at all isn't the way we do things.
> > > > > > > >
> > > > > > > > And even if it means a muxed design, then the fix is to make it work
> > inside the
> > > > > > > > driver, not adding some hacky workaround through ACPI tricks.
> > > > > > > >
> > > > > > > > And what out of tree drivers do or do not support we don't care one
> > bit anyway.
> > > > > > > >
> > > > > > >
> > > > > > > I think the reverts should be merged via Rafael's tree as the original
> > > > > > > patches went in via there, and we should get them in asap.
> > > > > > >
> > > > > > > Acked-by: Dave Airlie <airlied@redhat.com>
> > > > > > > Dave.
> > > > > >
> > > > > > There are definitely going to be regressions on machines in the field with
> > the
> > > > > > in tree drivers by reverting this.  I think we should have an answer for all
> > of those
> > > > > > before this revert is accepted.
> > > > > >
> > > > > > Regarding systems with Intel+NVIDIA, we'll have to work with partners to
> > collect
> > > > > > some information on the impact of reverting this.
> > > > > >
> > > > > > When this is used on a system with Intel+AMD the ASL configures AMD
> > GPU to use
> > > > > > "Hybrid Graphics" when on Windows and "Power Express" and
> > "Switchable Graphics"
> > > > > > when on Linux.
> > > > >
> > > > > and what's exactly the difference between those? And what's the actual
> > > > > issue here?
> > > >
> > > > Hybrid Graphics is the new "standard" way of handling these laptops.
> > > > It uses the standard _PR3 APCI method to handle dGPU power.  Support
> > > > for this was added to Linux relatively later compared to when the
> > > > laptops were launched.  "Power Express" used the other AMD specific
> > > > ATPX ACPI method to handle dGPU power.  The driver supports both so
> > > > either method will work.
> > > >
> > > > Alex
> > > >
> > >
> > > thanks for clarifying. But that still means that we won't need such
> > > workarounds for AMD users, right? amdgpu handles hybrid graphics just
> > > fine, right?
> >
> > Yeah it should, assuming you have a new enough kernel which supports
> > HG, which has been several years at this point IIRC.
> >
> > Alex
> >
>
> Can you define how new of a kernel is a new enough kernel?
>
> Looking on my side these problems were on new hardware (Precision 7740) and
> are checked as recently as start of this summer, w/ kernel 4.15.

I don't remember off hand.  It was before the _PR3 support in the pci
subsystem was upstream.  What was the problem you were seeing with
this system?

Alex

>
> We can arrange to have it checked again on 5.3rcX w/ the OSI disabled.