linux-kernel - Re: [PATCH 2/2] ACPI: processor: idle: Remove obsolete comment

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAJZ5v0gC3DzanSdPqQiJ4JQppgNeRA7Z9Cge7NxmTO_shoUyOA@mail.gmail.com>
Date: Mon, 31 Mar 2025 14:07:13 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: "Zhang, Rui" <rui.zhang@...el.com>
Cc: Giovanni Gherdovich <ggherdovich@...e.cz>, "Rafael J . Wysocki" <rafael@...nel.org>, Len Brown <lenb@...nel.org>, 
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH 2/2] ACPI: processor: idle: Remove obsolete comment

On Mon, Mar 31, 2025 at 9:38 AM Zhang, Rui <rui.zhang@...el.com> wrote:
>
> > -----Original Message-----
> > From: Giovanni Gherdovich <ggherdovich@...e.cz>
> > Sent: Friday, March 28, 2025 10:31 PM
> > To: Rafael J . Wysocki <rafael@...nel.org>; Zhang, Rui <rui.zhang@...el.com>
> > Cc: Len Brown <lenb@...nel.org>; Giovanni Gherdovich
> > <ggherdovich@...e.cz>; linux-acpi@...r.kernel.org; linux-
> > kernel@...r.kernel.org; linux-pm@...r.kernel.org
> > Subject: [PATCH 2/2] ACPI: processor: idle: Remove obsolete comment
> > Importance: High
> >
> > Since commit 496121c02127e9c460b436244c38260b044cc45a ("ACPI:
> > processor:
> > idle: Allow probing on platforms with one ACPI C-state"), the comment
> > doesn't reflect the code anymore; remove it.
> >
> > Signed-off-by: Giovanni Gherdovich <ggherdovich@...e.cz>
> > ---
> >  drivers/acpi/processor_idle.c | 4 ----
> >  1 file changed, 4 deletions(-)
> >
> > diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
> > index b181f7fc2090..2a076c7a825a 100644
> > --- a/drivers/acpi/processor_idle.c
> > +++ b/drivers/acpi/processor_idle.c
> > @@ -482,10 +482,6 @@ static int acpi_processor_get_cstate_info(struct
> > acpi_processor *pr)
> >
> >       pr->power.count = acpi_processor_power_verify(pr);
> >
> > -     /*
> > -      * if one state of type C2 or C3 is available, mark this
> > -      * CPU as being "idle manageable"
> > -      */
> >       for (i = 1; i < ACPI_PROCESSOR_MAX_POWER; i++) {
> >               if (pr->power.states[i].valid) {
> >                       pr->power.count = i;
> > --
> > 2.43.0
>
> I think we can clean up a bit more. How about the patch below?
>
> From 115d3a07febff32eed49f9343ef111e7e1452f9d Mon Sep 17 00:00:00 2001
> From: "Zhang, Rui" <rui.zhang@...el.com>
> Date: Mon, 31 Mar 2025 07:29:57 +0000
> Subject: [PATCH] ACPI: processor: idle: Simplify
>  acpi_processor_get_cstate_info() logic
>
> Since commit 496121c02127 ("ACPI: processor: idle: Allow probing on
> platforms with one ACPI C-state"), acpi_idle driver can be probed with
> C1 only.
>
> Optimize the logic for setting pr->power.count and pr->flags.power by
> 1. unconditionally set pr->flags.power leveraging the fact that C1 is
>    always valid after acpi_processor_get_power_info_default().
> 2. update acpi_processor_power_verify() to return the highest valid
>    C-state directly.
>
> No functional change intended.
>
> Signed-off-by: Zhang Rui <rui.zhang@...el.com>
> ---
>  drivers/acpi/processor_idle.c | 15 ++-------------
>  1 file changed, 2 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
> index 698897b29de2..7ce8c3802937 100644
> --- a/drivers/acpi/processor_idle.c
> +++ b/drivers/acpi/processor_idle.c
> @@ -442,7 +442,7 @@ static int acpi_processor_power_verify(struct acpi_processor *pr)
>
>                 lapic_timer_check_state(i, pr, cx);
>                 tsc_check_state(cx->type);
> -               working++;
> +               working = i;

What if some states are skipped because they are invalid?  'working'
can be less than 'i' then AFAICS.

>         }
>
>         if (buggy_latency) {
> @@ -457,7 +457,6 @@ static int acpi_processor_power_verify(struct acpi_processor *pr)
>
>  static int acpi_processor_get_cstate_info(struct acpi_processor *pr)
>  {
> -       unsigned int i;
>         int result;
>
>
> @@ -477,17 +476,7 @@ static int acpi_processor_get_cstate_info(struct acpi_processor *pr)
>         acpi_processor_get_power_info_default(pr);
>
>         pr->power.count = acpi_processor_power_verify(pr);
> -
> -       /*
> -        * if one state of type C2 or C3 is available, mark this
> -        * CPU as being "idle manageable"
> -        */
> -       for (i = 1; i < ACPI_PROCESSOR_MAX_POWER; i++) {
> -               if (pr->power.states[i].valid) {
> -                       pr->power.count = i;
> -                       pr->flags.power = 1;
> -               }
> -       }
> +       pr->flags.power = 1;
>
>         return 0;
>  }
> --