linux-kernel - Re: [PATCH v6 3/7] powercap/drivers/dtpm: Simplify the dtpm table

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Message-ID: <CAAYoRsURO1tf03nfiki1uaXYEmTKQyYKUeTyKW+vefrVzCO7jg@mail.gmail.com>
Date:   Fri, 26 Nov 2021 09:08:25 -0800
From:   Doug Smythies <dsmythies@...us.net>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     Linux PM list <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        lukasz.luba@....com, "Rafael J. Wysocki" <rafael@...nel.org>,
        gregkh@...uxfoundation.org, dsmythies <dsmythies@...us.net>
Subject: Re: [PATCH v6 3/7] powercap/drivers/dtpm: Simplify the dtpm table

Hi Daniel,

This patch introduces a regression, at least on my test system.
I can no longer change CPU frequency scaling drivers, for example
from intel_cpufreq (A.K.A intel_pstate in passive mode) to intel_pstate
(A.K.A. active mode). The task just hangs forever.

I bisected the kernel and got this commit as the result.
As a double check, I reverted this commit:
7a89d7eacf8e84f2afb94db5ae9d9f9faa93f01c
on kernel 5.16-rc2 and the issue was resolved.

While your email is fairly old, I observe that it was only included as of
kernel 5.16-rc1.

Command Example that never completes:

$ echo passive | sudo tee /sys/devices/system/cpu/intel_pstate/status

syslog excerpt attached.

... Doug

On Thu, Apr 1, 2021 at 12:24 PM Daniel Lezcano
<daniel.lezcano@...aro.org> wrote:
>
> The dtpm table is an array of pointers, that forces the user of the
> table to define initdata along with the declaration of the table
> entry. It is more efficient to create an array of dtpm structure, so
> the declaration of the table entry can be done by initializing the
> different fields.
>
> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
> Reviewed-by: Lukasz Luba <lukasz.luba@....com>
> ---
>  drivers/powercap/dtpm.c     |  4 ++--
>  drivers/powercap/dtpm_cpu.c |  4 +++-
>  include/linux/dtpm.h        | 20 +++++++++-----------
>  3 files changed, 14 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/powercap/dtpm.c b/drivers/powercap/dtpm.c
> index a707cc2965a1..d9aac107c927 100644
> --- a/drivers/powercap/dtpm.c
> +++ b/drivers/powercap/dtpm.c
> @@ -583,7 +583,7 @@ int dtpm_register(const char *name, struct dtpm *dtpm, struct dtpm *parent)
>
>  static int __init dtpm_init(void)
>  {
> -       struct dtpm_descr **dtpm_descr;
> +       struct dtpm_descr *dtpm_descr;
>
>         pct = powercap_register_control_type(NULL, "dtpm", NULL);
>         if (IS_ERR(pct)) {
> @@ -592,7 +592,7 @@ static int __init dtpm_init(void)
>         }
>
>         for_each_dtpm_table(dtpm_descr)
> -               (*dtpm_descr)->init(*dtpm_descr);
> +               dtpm_descr->init();
>
>         return 0;
>  }
> diff --git a/drivers/powercap/dtpm_cpu.c b/drivers/powercap/dtpm_cpu.c
> index 9deafd16a197..74b39a1082e5 100644
> --- a/drivers/powercap/dtpm_cpu.c
> +++ b/drivers/powercap/dtpm_cpu.c
> @@ -204,7 +204,7 @@ static int cpuhp_dtpm_cpu_online(unsigned int cpu)
>         return ret;
>  }
>
> -int dtpm_register_cpu(struct dtpm *parent)
> +static int __init dtpm_cpu_init(void)
>  {
>         int ret;
>
> @@ -241,3 +241,5 @@ int dtpm_register_cpu(struct dtpm *parent)
>
>         return 0;
>  }
> +
> +DTPM_DECLARE(dtpm_cpu, dtpm_cpu_init);
> diff --git a/include/linux/dtpm.h b/include/linux/dtpm.h
> index 577c71d4e098..2ec2821111d1 100644
> --- a/include/linux/dtpm.h
> +++ b/include/linux/dtpm.h
> @@ -33,25 +33,23 @@ struct dtpm_ops {
>         void (*release)(struct dtpm *);
>  };
>
> -struct dtpm_descr;
> -
> -typedef int (*dtpm_init_t)(struct dtpm_descr *);
> +typedef int (*dtpm_init_t)(void);
>
>  struct dtpm_descr {
> -       struct dtpm *parent;
> -       const char *name;
>         dtpm_init_t init;
>  };
>
>  /* Init section thermal table */
> -extern struct dtpm_descr *__dtpm_table[];
> -extern struct dtpm_descr *__dtpm_table_end[];
> +extern struct dtpm_descr __dtpm_table[];
> +extern struct dtpm_descr __dtpm_table_end[];
>
> -#define DTPM_TABLE_ENTRY(name)                 \
> -       static typeof(name) *__dtpm_table_entry_##name  \
> -       __used __section("__dtpm_table") = &name
> +#define DTPM_TABLE_ENTRY(name, __init)                         \
> +       static struct dtpm_descr __dtpm_table_entry_##name      \
> +       __used __section("__dtpm_table") = {                    \
> +               .init = __init,                                 \
> +       }
>
> -#define DTPM_DECLARE(name)     DTPM_TABLE_ENTRY(name)
> +#define DTPM_DECLARE(name, init)       DTPM_TABLE_ENTRY(name, init)
>
>  #define for_each_dtpm_table(__dtpm)    \
>         for (__dtpm = __dtpm_table;     \
> --
> 2.17.1
>

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