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From: Huacai Chen <chenhuacai@kernel.org>
Date: Fri, 14 Jun 2024 10:32:50 +0800
Message-ID: <CAAhV-H5C0rn-bY11FxoGANX+hEFrrbpj095ZAEbjC0ksQGuWpA@mail.gmail.com>
Subject: Re: [PATCH 2/2] LoongArch: Fix ACPI standard register based S3 support
To: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: Jianmin Lv <lvjianmin@loongson.cn>, Xuerui Wang <kernel@xen0n.name>, loongarch@lists.linux.dev, 
	linux-kernel@vger.kernel.org, 
	"stable@vger.kernel.org" <stable@vger.kernel.org>
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On Fri, Jun 14, 2024 at 10:25=E2=80=AFAM Jiaxun Yang <jiaxun.yang@flygoat.c=
om> wrote:
>
>
>
> =E5=9C=A82024=E5=B9=B46=E6=9C=8814=E6=97=A5=E5=85=AD=E6=9C=88 =E4=B8=8A=
=E5=8D=883:11=EF=BC=8CHuacai Chen=E5=86=99=E9=81=93=EF=BC=9A
> > Hi, Jiaxun,
> >
> > On Fri, Jun 14, 2024 at 12:41=E2=80=AFAM Jiaxun Yang <jiaxun.yang@flygo=
at.com> wrote:
> >>
> >> Most LoongArch 64 machines are using custom "SADR" ACPI extension
> >> to perform ACPI S3 sleep. However the standard ACPI way to perform
> >> sleep is to write a value to ACPI PM1/SLEEP_CTL register, and this
> >> is never supported properly in kernel.
> > Maybe our hardware is insane so we need "SADR", if so, this patch may
> > break real hardware. What's your opinion, Jianmin?
>
> I understand why your hardware need SADR. Most systems DDR self-refresh
> mode needs to be setup by firmware.
_S3 is also a firmware method, why we can't use it to setup self-refresh?

Huacai

>
> There is no chance that it may break real hardware. When firmware supplie=
d
> SADR it will always use SADR. The fallback only happens when _S3 method e=
xist
> but no SADR supplied, which won't happen on real hardware.
>
> For QEMU we don't have stub firmware but standard compliant SEEP_CTL is
> sufficient for entering sleep mode, thus we need this fallback path.
>
> Thanks
>
> >
> > Huacai
> >
> >>
>
> --
> - Jiaxun
>