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Date:   Wed, 20 Nov 2019 13:51:27 +0200
From:   Mika Westerberg <mika.westerberg@intel.com>
To:     "Rafael J. Wysocki" <rafael@kernel.org>
Cc:     Karol Herbst <kherbst@redhat.com>,
        Bjorn Helgaas <helgaas@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Lyude Paul <lyude@redhat.com>,
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        Dave Airlie <airlied@gmail.com>,
        Mario Limonciello <Mario.Limonciello@dell.com>
Subject: Re: [PATCH v4] pci: prevent putting nvidia GPUs into lower device
 states on certain intel bridges
Message-ID: <20191120115127.GD11621@lahna.fi.intel.com>
References: <20191017121901.13699-1-kherbst@redhat.com>
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On Wed, Nov 20, 2019 at 01:22:16PM +0200, Mika Westerberg wrote:
>             If (((OSYS <= 0x07D9) || ((OSYS == 0x07DF) && (_REV == 
>                 0x05))))
>             {

The OSYS comes from this (in DSDT):

                If (_OSI ("Windows 2009"))
                {
                    OSYS = 0x07D9
                }

                If (_OSI ("Windows 2012"))
                {
                    OSYS = 0x07DC
                }

                If (_OSI ("Windows 2013"))
                {
                    OSYS = 0x07DD
                }

                If (_OSI ("Windows 2015"))
                {
                    OSYS = 0x07DF
                }

So I guess this particular check tries to identify Windows 7 and older,
and Linux.

>                 If ((PIOF == Zero))
>                 {
>                     P0LD = One
>                     TCNT = Zero
>                     While ((TCNT < LDLY))
>                     {
>                         If ((P0LT == 0x08))
>                         {
>                             Break
>                         }
> 
>                         Sleep (0x10)
>                         TCNT += 0x10
>                     }
> 
>                     P0RM = One
>                     P0AP = 0x03
>                 }
>                 ElseIf ((PIOF == One))
>                 {
>                     P1LD = One
>                     TCNT = Zero
>                     While ((TCNT < LDLY))
>                     {
>                         If ((P1LT == 0x08))
>                         {
>                             Break
>                         }
> 
>                         Sleep (0x10)
>                         TCNT += 0x10
>                     }
> 
>                     P1RM = One
>                     P1AP = 0x03
>                 }
>                 ElseIf ((PIOF == 0x02))
>                 {
>                     P2LD = One
>                     TCNT = Zero
>                     While ((TCNT < LDLY))
>                     {
>                         If ((P2LT == 0x08))
>                         {
>                             Break
>                         }
> 
>                         Sleep (0x10)
>                         TCNT += 0x10
>                     }
> 
>                     P2RM = One
>                     P2AP = 0x03
>                 }
> 
>                 If ((PBGE != Zero))
>                 {
>                     If (SBDL (PIOF))
>                     {
>                         MBDL = GMXB (PIOF)
>                         PDUB (PIOF, MBDL)
>                     }
>                 }
>             }
>             Else
>             {
>                 LKDS (PIOF)
>             }
> 
>             If ((DerefOf (SCLK [Zero]) != Zero))
>             {
>                 PCRO (0xDC, 0x100C, DerefOf (SCLK [One]))
>                 Sleep (0x10)
>             }
> 
>             GPPR (PIOF, Zero)
>             If ((OSYS != 0x07D9))
>             {
>                 DIWK (PIOF)
>             }
> 
>             \_SB.SGOV (0x01010004, Zero)
>             Sleep (0x14)
>             Return (Zero)
>         }