linux-kernel - Re: [PATCH v3 3/4] LoongArch: Save and restore PERCPU_BASE

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Date: Sat, 13 Apr 2024 15:22:55 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Tiezhu Yang <yangtiezhu@...ngson.cn>
Cc: Thomas Gleixner <tglx@...utronix.de>, Arnd Bergmann <arnd@...db.de>, Marc Zyngier <maz@...nel.org>, 
	loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	loongson-kernel@...ts.loongnix.cn
Subject: Re: [PATCH v3 3/4] LoongArch: Save and restore PERCPU_BASE_KS for
 ACPI S3 state

On Fri, Apr 12, 2024 at 5:30 PM Tiezhu Yang <yangtiezhu@...ngson.cn> wrote:
>
>
>
> On 04/12/2024 12:18 PM, Huacai Chen wrote:
> > Hi, Tiezhu,
> >
> > On Thu, Apr 11, 2024 at 9:05 AM Tiezhu Yang <yangtiezhu@...ngson.cn> wrote:
> >>
> >> Currently, per_cpu_offset(x) is defined as __per_cpu_offset[x])
> >> only under CONFIG_SMP in include/asm-generic/percpu.h, that is
> >> to say, the implementation of loongarch_common_resume() which
> >> calls per_cpu_offset(0) is not suitable for the case of non-SMP,
> >> so do not write per_cpu_offset(0) to PERCPU_BASE_KS when resume,
> >> just save the value of PERCPU_BASE_KS when suspend and restore
> >> it when resume to make it work well for both SMP and non-SMP.
> > For non-SMP you need PERCPU_BASE_KS to do what?
>
> The initial aim is to avoid build error under !CONFIG_SMP
> and it works well on both !CONFIG_SMP and CONFIG_SMP, the
> changes are similar with the code in hibernate.c.
>
> An alternative way is to do the following simple change,
> but it seems a little ugly due to the ifdef, let me know
> what is your preference.
Add "u64 pcpu_base" at the last of saved_registers is better than this
patch, and can avoid ifdef.

Huacai

>
> diff --git a/arch/loongarch/power/suspend.c b/arch/loongarch/power/suspend.c
> index 166d9e06a64b..35191afefcda 100644
> --- a/arch/loongarch/power/suspend.c
> +++ b/arch/loongarch/power/suspend.c
> @@ -44,7 +44,9 @@ void loongarch_common_resume(void)
>   {
>          sync_counter();
>          local_flush_tlb_all();
> +#ifdef
>          csr_write64(per_cpu_offset(0), PERCPU_BASE_KS);
> +#endif
>          csr_write64(eentry, LOONGARCH_CSR_EENTRY);
>          csr_write64(eentry, LOONGARCH_CSR_MERRENTRY);
>          csr_write64(tlbrentry, LOONGARCH_CSR_TLBRENTRY);
>
> Thanks,
> Tiezhu
>
>