linux-kernel - Re: [PATCH v2 3/3] PM: runtime: Update kerneldoc return codes

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Message-ID: <aNaGUmOUfVsKazGr@kekkonen.localdomain>
Date: Fri, 26 Sep 2025 15:25:54 +0300
From: Sakari Ailus <sakari.ailus@...ux.intel.com>
To: Brian Norris <briannorris@...omium.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>,
	Pavel Machek <pavel@...nel.org>,
	"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
	Len Brown <lenb@...nel.org>, linux-kernel@...r.kernel.org,
	kunit-dev@...glegroups.com, linux-pm@...r.kernel.org
Subject: Re: [PATCH v2 3/3] PM: runtime: Update kerneldoc return codes

On Thu, Sep 25, 2025 at 12:42:16PM -0700, Brian Norris wrote:
> APIs based on __pm_runtime_idle() (pm_runtime_idle(), pm_request_idle())
> do not return 1 when already suspended. They return -EAGAIN. This is
> already covered in the docs, so the entry for "1" is redundant and
> conflicting.
> 
> (pm_runtime_put() and pm_runtime_put_sync() were previously incorrect,
> but that's fixed in "PM: runtime: pm_runtime_put{,_sync}() returns 1
> when already suspended", to ensure consistency with APIs like
> pm_runtime_put_autosuspend().)
> 
> RPM_GET_PUT APIs based on __pm_runtime_suspend() do return 1 when
> already suspended, but the language is a little unclear -- it's not
> really an "error", so it seems better to list as a clarification before
> the 0/success case. Additionally, they only actually return 1 when the
> refcount makes it to 0; if the usage counter is still non-zero, we
> return 0.
> 
> pm_runtime_put(), etc., also don't appear at first like they can ever
> see "-EAGAIN: Runtime PM usage_count non-zero", because in non-racy
> conditions, pm_runtime_put() would drop its reference count, see it's
> non-zero, and return early (in __pm_runtime_idle()). However, it's
> possible to race with another actor that increments the usage_count
> afterward, since rpm_idle() is protected by a separate lock; in such a
> case, we may see -EAGAIN.
> 
> Because this case is only seen in the presence of concurrent actors, it
> makes sense to clarify that this is when "usage_count **became**
> non-zero", by way of some racing actor.
> 
> Lastly, pm_runtime_put_sync_suspend() duplicated some -EAGAIN language.
> Fix that.
> 
> Fixes: 271ff96d6066 ("PM: runtime: Document return values of suspend-related API functions")
> Link: https://lore.kernel.org/linux-pm/aJ5pkEJuixTaybV4@google.com/
> Signed-off-by: Brian Norris <briannorris@...omium.org>

Reviewed-by: Sakari Ailus <sakari.ailus@...ux.intel.com>

-- 
Sakari Ailus