linux-kernel - Re: [PATCH 2/2] LoongArch: Fix ACPI standard register based S3 support

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Date: Fri, 14 Jun 2024 10:32:50 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Jiaxun Yang <jiaxun.yang@...goat.com>
Cc: Jianmin Lv <lvjianmin@...ngson.cn>, Xuerui Wang <kernel@...0n.name>, loongarch@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, 
	"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH 2/2] LoongArch: Fix ACPI standard register based S3 support

On Fri, Jun 14, 2024 at 10:25 AM Jiaxun Yang <jiaxun.yang@...goat.com> wrote:
>
>
>
> 在2024年6月14日六月 上午3:11，Huacai Chen写道：
> > Hi, Jiaxun,
> >
> > On Fri, Jun 14, 2024 at 12:41 AM Jiaxun Yang <jiaxun.yang@...goat.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 supplied
> SADR it will always use SADR. The fallback only happens when _S3 method exist
> 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
>