linux-kernel - Re: [RFC PATCH 2/7] arm64: kernel: Add a WFI hook.

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Message-Id: <5403A355-A4FA-442B-8F8B-5629FCECC006@caramail.com>
Date:   Thu, 21 Jan 2021 12:01:35 +0100
From:   Mohamed Mediouni <mohamed.mediouni@...amail.com>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Hector Martin <marcan@...can.st>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>,
        Stan Skowronek <stan@...ellium.com>
Subject: Re: [RFC PATCH 2/7] arm64: kernel: Add a WFI hook.



> On 21 Jan 2021, at 11:52, Arnd Bergmann <arnd@...nel.org> wrote:
> 
> On Wed, Jan 20, 2021 at 2:27 PM Mohamed Mediouni
> <mohamed.mediouni@...amail.com> wrote:
>> --- a/arch/arm64/kernel/cpu_ops.c
>> +++ b/arch/arm64/kernel/cpu_ops.c
> 
>> #if defined(CONFIG_STACKPROTECTOR) && !defined(CONFIG_STACKPROTECTOR_PER_TASK)
>> #include <linux/stackprotector.h>
>> @@ -74,8 +75,14 @@ void (*arm_pm_restart)(enum reboot_mode reboot_mode, const char *cmd);
>> 
>> static void noinstr __cpu_do_idle(void)
>> {
>> -       dsb(sy);
>> -       wfi();
>> +       const struct cpu_operations *ops = get_cpu_ops(task_cpu(current));
>> +
>> +       if (ops->cpu_wfi) {
>> +               ops->cpu_wfi();
>> +       } else {
>> +               dsb(sy);
>> +               wfi();
>> +       }
>> }
> 
> I think the correct place to put this would be a platform specific driver
> in drivers/cpuidle/ instead of an added low-level callback in the
> default idle function and a custom cpu_operations structure.
Can we make sure that wfi never gets called even on early
boot when using a cpuidle driver?

Thank you,
> 
>       Arnd