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

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Date: Fri, 12 Apr 2024 17:30:04 +0800
From: Tiezhu Yang <yangtiezhu@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>
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 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.

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