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From:   Grzegorz Jaszczyk <jaz@semihalf.com>
Date:   Wed, 20 Jul 2022 17:54:56 +0200
Message-ID: <CAH76GKNie4m=SOEEJGks+CEyR9=aB+dJzDA1wxTuUo=uUjmZog@mail.gmail.com>
Subject: Re: [RFC PATCH 1/2] suspend: extend S2Idle ops by new notify handler
To:     "Limonciello, Mario" <mario.limonciello@amd.com>
Cc:     "Rafael J. Wysocki" <rafael@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Dmytro Maluka <dmy@semihalf.com>,
        Sean Christopherson <seanjc@google.com>,
        Dominik Behr <dbehr@google.com>, upstream@semihalf.com,
        Zide Chen <zide.chen@intel.corp-partner.google.com>,
        Len Brown <lenb@kernel.org>,
        Hans de Goede <hdegoede@redhat.com>,
        Mark Gross <markgross@kernel.org>, Pavel Machek <pavel@ucw.cz>,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        Sachi King <nakato@nakato.io>,
        "open list:ACPI" <linux-acpi@vger.kernel.org>,
        "open list:X86 PLATFORM DRIVERS" 
        <platform-driver-x86@vger.kernel.org>,
        "open list:HIBERNATION (aka Software Suspend, aka swsusp)" 
        <linux-pm@vger.kernel.org>
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=C5=9Br., 20 lip 2022 o 17:22 Limonciello, Mario
<mario.limonciello@amd.com> napisa=C5=82(a):
>
> >> It looks like you want suspend-to-idle to behave like S3 and it won't.
> >
> > In a way, yes, we compensate for the lack of something like PM1_CNT to
> > trap on for detecting that the guest is suspending.
> > We could instead force the guest to use S3 but IMO it is undesirable,
> > since it generally does make a difference which suspend mode is used
> > in the guest, s2idle or S3, e.g some drivers check which suspend type
> > is used and based on that behaves differently during suspend. One of
> > the example is:
> > https://nam11.safelinks.protection.outlook.com/?url=3Dhttps%3A%2F%2Feli=
xir.bootlin.com%2Flinux%2Fv5.18.12%2Fsource%2Fdrivers%2Fgpu%2Fdrm%2Famd%2Fa=
mdgpu%2Famdgpu_drv.c%23L2323&amp;data=3D05%7C01%7Cmario.limonciello%40amd.c=
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n3iRybQzSFi3ojQ4YTJuW41DlgJNl5sxbWEvLBQ%3D&amp;reserved=3D0
> > https://nam11.safelinks.protection.outlook.com/?url=3Dhttps%3A%2F%2Feli=
xir.bootlin.com%2Flinux%2Fv5.18.12%2Fsource%2Fdrivers%2Fgpu%2Fdrm%2Famd%2Fa=
mdgpu%2Famdgpu_acpi.c%23L1069&amp;data=3D05%7C01%7Cmario.limonciello%40amd.=
com%7C7bdd972291324d03847e08da6a51ff4f%7C3dd8961fe4884e608e11a82d994e183d%7=
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LmZAgpIRPYO4to4uYUoBSEWXmz1lr%2BTnR14kAfvM%3D&amp;reserved=3D0
> > https://nam11.safelinks.protection.outlook.com/?url=3Dhttps%3A%2F%2Feli=
xir.bootlin.com%2Flinux%2Fv5.18.12%2Fsource%2Fdrivers%2Fgpu%2Fdrm%2Famd%2Fa=
mdgpu%2Famdgpu_gfx.c%23L583&amp;data=3D05%7C01%7Cmario.limonciello%40amd.co=
m%7C7bdd972291324d03847e08da6a51ff4f%7C3dd8961fe4884e608e11a82d994e183d%7C0=
%7C0%7C637939197694682503%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQI=
joiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=3DSNsbm=
pV4HrgA%2Bkff4JzRodNDzKvwM5tnkGDvrKO44dc%3D&amp;reserved=3D0
> >
>
> Actually I recently was suggesting a change to add this detection to
> another driver to set a policy and Rafael pushed back.  He's actively
> removing it from other places in the kernel.
>
> For amdgpu stuff you pointed above, are you wanting to pass through the
> PCIe GPU device to a guest and then suspend that guest? Or is this just
> illustrative?

Just illustrative. I am not focused on amdgpu stuff right now.

Thank you,
Grzegorz

>
> For a dGPU I would expect it works, but I don't think passing an APU's
> GPU PCIe endpoint would functionally work (there were bugs reported on
> this I recall).
>
> That code path you point out only has special handling for APU when
> headed to S0ix and that's because the GPU driver happens to be where the
> control point is for some common silicon functions.  If the bug I
> mentioned about PCIe passthrough of the APU GPU endpoint to the guest is
> fixed and the guest needs to do s0ix when the host doesn't we're going
> to have other breakage to worry about because of that common silicon
> functionality I mentioned.