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From:   Karol Herbst <kherbst@redhat.com>
Date:   Wed, 20 Nov 2019 12:58:00 +0100
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Subject: Re: [PATCH v4] pci: prevent putting nvidia GPUs into lower device
 states on certain intel bridges
To:     Mika Westerberg <mika.westerberg@intel.com>
Cc:     "Rafael J. Wysocki" <rafael@kernel.org>,
        Bjorn Helgaas <helgaas@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Lyude Paul <lyude@redhat.com>,
        "Rafael J . Wysocki" <rjw@rjwysocki.net>,
        Linux PCI <linux-pci@vger.kernel.org>,
        Linux PM <linux-pm@vger.kernel.org>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        nouveau <nouveau@lists.freedesktop.org>,
        Dave Airlie <airlied@gmail.com>,
        Mario Limonciello <Mario.Limonciello@dell.com>
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overall, what I really want to know is, _why_ does it work on windows?
Or what are we doing differently on Linux so that it doesn't work? If
anybody has any idea on how we could dig into this and figure it out
on this level, this would probably allow us to get closer to the root
cause? no?

On Wed, Nov 20, 2019 at 12:54 PM Karol Herbst <kherbst@redhat.com> wrote:
>
> for newer Windows the firmware uses bit  0x80 on 0x248 (Q0L2 being the
> field name) on the bridge controller to turn of the device, on other
> versions it uses the "older"? 0xb0 register and the P0LD field, which
> is documented, where the former is not.
>
> On Wed, Nov 20, 2019 at 12:51 PM Mika Westerberg
> <mika.westerberg@intel.com> wrote:
> >
> > On Wed, Nov 20, 2019 at 01:22:16PM +0200, Mika Westerberg wrote:
> > >             If (((OSYS <=3D 0x07D9) || ((OSYS =3D=3D 0x07DF) && (_REV=
 =3D=3D
> > >                 0x05))))
> > >             {
> >
> > The OSYS comes from this (in DSDT):
> >
> >                 If (_OSI ("Windows 2009"))
> >                 {
> >                     OSYS =3D 0x07D9
> >                 }
> >
> >                 If (_OSI ("Windows 2012"))
> >                 {
> >                     OSYS =3D 0x07DC
> >                 }
> >
> >                 If (_OSI ("Windows 2013"))
> >                 {
> >                     OSYS =3D 0x07DD
> >                 }
> >
> >                 If (_OSI ("Windows 2015"))
> >                 {
> >                     OSYS =3D 0x07DF
> >                 }
> >
> > So I guess this particular check tries to identify Windows 7 and older,
> > and Linux.
> >
> > >                 If ((PIOF =3D=3D Zero))
> > >                 {
> > >                     P0LD =3D One
> > >                     TCNT =3D Zero
> > >                     While ((TCNT < LDLY))
> > >                     {
> > >                         If ((P0LT =3D=3D 0x08))
> > >                         {
> > >                             Break
> > >                         }
> > >
> > >                         Sleep (0x10)
> > >                         TCNT +=3D 0x10
> > >                     }
> > >
> > >                     P0RM =3D One
> > >                     P0AP =3D 0x03
> > >                 }
> > >                 ElseIf ((PIOF =3D=3D One))
> > >                 {
> > >                     P1LD =3D One
> > >                     TCNT =3D Zero
> > >                     While ((TCNT < LDLY))
> > >                     {
> > >                         If ((P1LT =3D=3D 0x08))
> > >                         {
> > >                             Break
> > >                         }
> > >
> > >                         Sleep (0x10)
> > >                         TCNT +=3D 0x10
> > >                     }
> > >
> > >                     P1RM =3D One
> > >                     P1AP =3D 0x03
> > >                 }
> > >                 ElseIf ((PIOF =3D=3D 0x02))
> > >                 {
> > >                     P2LD =3D One
> > >                     TCNT =3D Zero
> > >                     While ((TCNT < LDLY))
> > >                     {
> > >                         If ((P2LT =3D=3D 0x08))
> > >                         {
> > >                             Break
> > >                         }
> > >
> > >                         Sleep (0x10)
> > >                         TCNT +=3D 0x10
> > >                     }
> > >
> > >                     P2RM =3D One
> > >                     P2AP =3D 0x03
> > >                 }
> > >
> > >                 If ((PBGE !=3D Zero))
> > >                 {
> > >                     If (SBDL (PIOF))
> > >                     {
> > >                         MBDL =3D GMXB (PIOF)
> > >                         PDUB (PIOF, MBDL)
> > >                     }
> > >                 }
> > >             }
> > >             Else
> > >             {
> > >                 LKDS (PIOF)
> > >             }
> > >
> > >             If ((DerefOf (SCLK [Zero]) !=3D Zero))
> > >             {
> > >                 PCRO (0xDC, 0x100C, DerefOf (SCLK [One]))
> > >                 Sleep (0x10)
> > >             }
> > >
> > >             GPPR (PIOF, Zero)
> > >             If ((OSYS !=3D 0x07D9))
> > >             {
> > >                 DIWK (PIOF)
> > >             }
> > >
> > >             \_SB.SGOV (0x01010004, Zero)
> > >             Sleep (0x14)
> > >             Return (Zero)
> > >         }
> >