linux-kernel - Re: [PATCH][v2] PM / sleep: Add pm_debug

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Date:   Wed, 1 Apr 2020 11:43:51 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Chen Yu <yu.c.chen@...el.com>
Cc:     Linux PM <linux-pm@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>, Pavel Machek <pavel@....cz>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH][v2] PM / sleep: Add pm_debug_messages boot command control

On Sun, Mar 29, 2020 at 4:48 PM Chen Yu <yu.c.chen@...el.com> wrote:
>
> Debug messages from the system suspend/hibernation infrastructure
> is disabled by default, and can only be enabled after the system
> has boot up via /sys/power/pm_debug_messages. This makes the hibernation
> resume hard to track as it involves system boot up across hibernation.
> There's no chance for software_resume() to track the resume process,
> eg.
>
> Turning on the pm_debug_messages during boot up by appending
> 'pm_debug_message'.
>
> Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> Cc: Len Brown <lenb@...nel.org>
> Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Cc: Randy Dunlap <rdunlap@...radead.org>
> Signed-off-by: Chen Yu <yu.c.chen@...el.com>
> ---
> v2: According to Randy's suggestion, add the command line
>     option to Documentation/admin-guide/kernel-parameters.txt
> ---
>  Documentation/admin-guide/kernel-parameters.txt | 3 +++
>  kernel/power/main.c                             | 7 +++++++
>  2 files changed, 10 insertions(+)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index c07815d230bc..105ec73743d7 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -3698,6 +3698,9 @@
>                         Override pmtimer IOPort with a hex value.
>                         e.g. pmtmr=0x508
>
> +       pm_debug_message        [SUSPEND,KNL]
> +                       Enable suspend/resume debug messages during boot up.
> +
>         pnp.debug=1     [PNP]
>                         Enable PNP debug messages (depends on the
>                         CONFIG_PNP_DEBUG_MESSAGES option).  Change at run-time
> diff --git a/kernel/power/main.c b/kernel/power/main.c
> index 69b7a8aeca3b..1da3d7c15e03 100644
> --- a/kernel/power/main.c
> +++ b/kernel/power/main.c
> @@ -535,6 +535,13 @@ static ssize_t pm_debug_messages_store(struct kobject *kobj,
>
>  power_attr(pm_debug_messages);
>
> +static int __init pm_debug_message_setup(char *str)
> +{
> +       pm_debug_messages_on = true;
> +       return 1;
> +}
> +__setup("pm_debug_message", pm_debug_message_setup);

I'd call this "pm_debug_messages" (just like the sysfs knob) and
rename the rest accordingly.

> +
>  /**
>   * __pm_pr_dbg - Print a suspend debug message to the kernel log.
>   * @defer: Whether or not to use printk_deferred() to print the message.
> --