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

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Date: Mon, 17 Jun 2024 21:49:50 +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 10:44 AM Jiaxun Yang <jiaxun.yang@...goat.com> wrote:
>
>
>
> 在2024年6月14日六月 上午3:32，Huacai Chen写道：
> > 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?
>
> That's the problem from ACPI spec. As per ACPI spec _S3 method only tells
> you what should you write into PM1 or SLEEP_CTL register, it will NOT perform
> actual task to enter sleeping. (See 16.1.3.1 [1])
>
> On existing LoongArch hardware _S3 method is only used to mark presence of S3
> state. This is violating ACPI spec, but I guess we must live with it.
>
> Furthermore, on Loongson hardware you have to disable access to DDR memory
> to access DDR controller's configuration registers. Which means self-refresh
> code must run from BIOS ROM.
>
> [1]: https://uefi.org/htmlspecs/ACPI_Spec_6_4_html/16_Waking_and_Sleeping/sleeping-states.html
I think "if (!acpi_gbl_reduced_hardware)" should be before "if
(!acpi_sleep_state_supported(ACPI_STATE_S3))", I applied this patch
with adjustment.

https://github.com/chenhuacai/linux/commit/4bb9e051a4e9430c89ce83ca68a2f5998926e6f6


Huacai

>
> Thanks
> - Jiaxun
>
> >
> > 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
> >>
>
> --
> - Jiaxun