linux-kernel - Re: [PATCH] drm: amd: amdgpu: ACPI: Add comment about ACPI_FADT_LOW_POWER

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Date:   Thu, 25 Aug 2022 11:48:17 -0400
From:   Alex Deucher <alexdeucher@...il.com>
To:     "Limonciello, Mario" <mario.limonciello@....com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Alex Deucher <alexander.deucher@....com>,
        Linux PM <linux-pm@...r.kernel.org>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        dri-devel@...ts.freedesktop.org,
        Linux ACPI <linux-acpi@...r.kernel.org>,
        amd-gfx@...ts.freedesktop.org,
        Christian König <christian.koenig@....com>
Subject: Re: [PATCH] drm: amd: amdgpu: ACPI: Add comment about ACPI_FADT_LOW_POWER_S0

Applied.  Thanks!

Alex

On Thu, Aug 25, 2022 at 3:58 AM Limonciello, Mario
<mario.limonciello@....com> wrote:
>
> On 8/24/2022 12:32, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> >
> > According to the ACPI specification [1], the ACPI_FADT_LOW_POWER_S0
> > flag merely means that it is better to use low-power S0 idle on the
> > given platform than S3 (provided that the latter is supported) and it
> > doesn't preclude using either of them (which of them will be used
> > depends on the choices made by user space).
> >
> > However, on some systems that flag is used to indicate whether or not
> > to enable special firmware mechanics allowing the system to save more
> > energy when suspended to idle.  If that flag is unset, doing so is
> > generally risky.
> >
> > Accordingly, add a comment to explain the ACPI_FADT_LOW_POWER_S0 check
> > in amdgpu_acpi_is_s0ix_active(), the purpose of which is otherwise
> > somewhat unclear.
> >
> > Link: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fuefi.org%2Fspecs%2FACPI%2F6.4%2F05_ACPI_Software_Programming_Model%2FACPI_Software_Programming_Model.html%23fixed-acpi-description-table-fadt&amp;data=05%7C01%7Cmario.limonciello%40amd.com%7Cf43320dda5114deeb16908da85f69d3b%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637969591512297179%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=xp8pNzsXCkLcIJOJFY77yaLkMrvz5he3S%2Bi%2FwaxTwwg%3D&amp;reserved=0 # [1]
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>
> Reviewed-by: Mario Limonciello <mario.limonciello@....com>
>
> > ---
> >   drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c |    6 ++++++
> >   1 file changed, 6 insertions(+)
> >
> > Index: linux-pm/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
> > ===================================================================
> > --- linux-pm.orig/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
> > +++ linux-pm/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
> > @@ -1066,6 +1066,12 @@ bool amdgpu_acpi_is_s0ix_active(struct a
> >           (pm_suspend_target_state != PM_SUSPEND_TO_IDLE))
> >               return false;
> >
> > +     /*
> > +      * If ACPI_FADT_LOW_POWER_S0 is not set in the FADT, it is generally
> > +      * risky to do any special firmware-related preparations for entering
> > +      * S0ix even though the system is suspending to idle, so return false
> > +      * in that case.
> > +      */
> >       if (!(acpi_gbl_FADT.flags & ACPI_FADT_LOW_POWER_S0)) {
> >               dev_warn_once(adev->dev,
> >                             "Power consumption will be higher as BIOS has not been configured for suspend-to-idle.\n"
> >
> >
> >
>