linux-kernel - Re: [PATCH] cpufreq: Simplify MSR read on the boot CPU

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Message-ID: <CAJZ5v0i0nf_8BGqbuFRQ6byxM9cPU4A37hiW10LZ57FTqDgO8w@mail.gmail.com>
Date: Tue, 12 Nov 2024 21:44:49 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: "Chang S. Bae" <chang.seok.bae@...el.com>
Cc: linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org, rafael@...nel.org, 
	viresh.kumar@...aro.org, dave.hansen@...el.com, bp@...en8.de
Subject: Re: [PATCH] cpufreq: Simplify MSR read on the boot CPU

On Wed, Nov 6, 2024 at 7:23 PM Chang S. Bae <chang.seok.bae@...el.com> wrote:
>
> Replace the 32-bit MSR access function with a 64-bit variant to simplify
> the call site, eliminating unnecessary 32-bit value manipulations.
>
> Signed-off-by: Chang S. Bae <chang.seok.bae@...el.com>
> Cc: Rafael J. Wysocki <rafael@...nel.org>
> Cc: Viresh Kumar <viresh.kumar@...aro.org>
> Cc: Dave Hansen <dave.hansen@...el.com>
> Cc: Borislav Petkov <bp@...en8.de>
> ---
> I've received feedback to use rdmsrl_on_cpu() instead of rdmsr_on_cpu()
> for similar code in my feature-enabling series [1]. While auditing the
> tree, I found this case as well, so here's another cleanup.
>
> [1] https://lore.kernel.org/lkml/e9afefb7-3c4e-48ee-aab1-2f338c4e989d@intel.com/
> ---
>  drivers/cpufreq/acpi-cpufreq.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/cpufreq/acpi-cpufreq.c b/drivers/cpufreq/acpi-cpufreq.c
> index 0f04feb6cafa..b942cd11e179 100644
> --- a/drivers/cpufreq/acpi-cpufreq.c
> +++ b/drivers/cpufreq/acpi-cpufreq.c
> @@ -73,20 +73,17 @@ static unsigned int acpi_pstate_strict;
>
>  static bool boost_state(unsigned int cpu)
>  {
> -       u32 lo, hi;
>         u64 msr;
>
>         switch (boot_cpu_data.x86_vendor) {
>         case X86_VENDOR_INTEL:
>         case X86_VENDOR_CENTAUR:
>         case X86_VENDOR_ZHAOXIN:
> -               rdmsr_on_cpu(cpu, MSR_IA32_MISC_ENABLE, &lo, &hi);
> -               msr = lo | ((u64)hi << 32);
> +               rdmsrl_on_cpu(cpu, MSR_IA32_MISC_ENABLE, &msr);
>                 return !(msr & MSR_IA32_MISC_ENABLE_TURBO_DISABLE);
>         case X86_VENDOR_HYGON:
>         case X86_VENDOR_AMD:
> -               rdmsr_on_cpu(cpu, MSR_K7_HWCR, &lo, &hi);
> -               msr = lo | ((u64)hi << 32);
> +               rdmsrl_on_cpu(cpu, MSR_K7_HWCR, &msr);
>                 return !(msr & MSR_K7_HWCR_CPB_DIS);
>         }
>         return false;
> --

Applied as 6.13 material, thanks!