linux-kernel - Re: [PATCH v3] clk: expand clk_ignore_unused mechanism to keep only a few clks on

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Message-ID: <4d8d412a33a7d63f2ffe6a13194375ed.sboyd@kernel.org>
Date:   Wed, 29 Mar 2023 12:49:19 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Michael Turquette <mturquette@...libre.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
Cc:     linux-doc@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel@...gutronix.de,
        Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH v3] clk: expand clk_ignore_unused mechanism to keep only a few clks on

Quoting Uwe Kleine-König (2022-10-26 08:18:12)
> Allow to pass an integer n that results in only keeping n unused clocks
> enabled.
> 
> This helps to debug the problem if you only know that clk_ignore_unused
> helps but you have no clue yet which clock is the culprit.
> 
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> ---
> Hello,
> 
> compared to v2 sent in August 2021 this is a trivial rebase on top of
> v6.1-rc1. I pinged that one repeatedly, I'm now trying with resending
> and calling the rebased patch v3 to maybe get some feedback. :-\
> 
> Best regards
> Uwe
> 
>  Documentation/driver-api/clk.rst |  4 +++-

No update to Documentation/admin-guide/kernel-parameters.txt?

>  drivers/clk/clk.c                | 33 ++++++++++++++++++++++++--------
>  2 files changed, 28 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index c3c3f8c07258..356119a7e5fe 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -1322,6 +1322,8 @@ static void __init clk_unprepare_unused_subtree(struct clk_core *core)
>         clk_pm_runtime_put(core);
>  }
>  
> +static unsigned clk_unused_keep_on __initdata;
> +
>  static void __init clk_disable_unused_subtree(struct clk_core *core)
>  {
>         struct clk_core *child;
> @@ -1352,12 +1354,17 @@ static void __init clk_disable_unused_subtree(struct clk_core *core)
>          * back to .disable
>          */
>         if (clk_core_is_enabled(core)) {
> -               trace_clk_disable(core);
> -               if (core->ops->disable_unused)
> -                       core->ops->disable_unused(core->hw);
> -               else if (core->ops->disable)
> -                       core->ops->disable(core->hw);
> -               trace_clk_disable_complete(core);
> +               if (clk_unused_keep_on) {
> +                       pr_warn("Keep unused clk \"%s\" on\n", core->name);
> +                       clk_unused_keep_on -= 1;
> +               } else {
> +                       trace_clk_disable(core);

We have trace_clk_disable() here. Can you have this tracepoint print to
the kernel log and watch over serial console? That would be faster than
bisecting.

> +                       if (core->ops->disable_unused)
> +                               core->ops->disable_unused(core->hw);
> +                       else if (core->ops->disable)
> +                               core->ops->disable(core->hw);
> +                       trace_clk_disable_complete(core);
> +               }
>         }
>  
>  unlock_out:
> @@ -1369,9 +1376,17 @@ static void __init clk_disable_unused_subtree(struct clk_core *core)
>  }
>  
>  static bool clk_ignore_unused __initdata;
> -static int __init clk_ignore_unused_setup(char *__unused)
> +static int __init clk_ignore_unused_setup(char *keep)
>  {
> -       clk_ignore_unused = true;
> +       if (*keep == '=') {
> +               int ret;
> +
> +               ret = kstrtouint(keep + 1, 0, &clk_unused_keep_on);
> +               if (ret < 0)

Could omit 'ret' and just have if (kstrtouint(..))

> +                       pr_err("Warning: failed to parse clk_ignore_unused parameter, ignoring");

Missing newline on printk.

> +       } else {
> +               clk_ignore_unused = true;
> +       }
>         return 1;
>  }
>  __setup("clk_ignore_unused", clk_ignore_unused_setup);