linux-kernel - Re: [PATCH 2/3] PM: runtime: Make put{,_sync}() return 1 when already suspended

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Message-ID: <20250924094809.g7vuy75vm3gqzc4d@lcpd911>
Date: Wed, 24 Sep 2025 15:18:09 +0530
From: Dhruva Gole <d-gole@...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>,
        <kunit-dev@...glegroups.com>, Len Brown <lenb@...nel.org>,
        Sakari Ailus
	<sakari.ailus@...ux.intel.com>,
        <linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] PM: runtime: Make put{,_sync}() return 1 when
 already suspended

On Aug 28, 2025 at 17:28:27 -0700, Brian Norris wrote:
> The pm_runtime.h docs say pm_runtime_put() and pm_runtime_put_sync()
> return 1 when already suspended, but this is not true -- they return
> -EAGAIN. On the other hand, pm_runtime_put_sync_suspend() and
> pm_runtime_put_sync_autosuspend() *do* return 1.
> 
> This is an artifact of the fact that the former are built on rpm_idle(),
> whereas the latter are built on rpm_suspend().
> 
> There are precious few pm_runtime_put()/pm_runtime_put_sync() callers
> that check the return code at all, but most of them only log errors, and
> usually only for negative error codes. None of them should be treating
> this as an error, so:
> 
>  * at best, this may fix some case where a driver treats this condition
>    as an error, when it shouldn't;
> 
>  * at worst, this should make no effect; and
> 
>  * somewhere in between, we could potentially clear up non-fatal log
>    messages.

Right, just doing a $> git grep -A5 "= pm_runtime_put"    gave me quite a few
callers who actually do check the return codes, and in some cases even
directly backpropagate them! So like you say with this patch best case even
might fix a few cases where it's unnecessary.


> 
> Fix the pm_runtime_already_suspended_test() while tweaking the behavior.
> The test makes a lot more sense when these all return 1 when the device
> is already suspended:
> 
>     pm_runtime_put(dev);
>     pm_runtime_put_sync(dev);
>     pm_runtime_suspend(dev);
>     pm_runtime_autosuspend(dev);
>     pm_request_autosuspend(dev);
>     pm_runtime_put_sync_autosuspend(dev);
>     pm_runtime_put_autosuspend(dev);
> 
> Signed-off-by: Brian Norris <briannorris@...omium.org>
> ---
> 
>  drivers/base/power/runtime-test.c | 8 ++------
>  drivers/base/power/runtime.c      | 3 +++
>  2 files changed, 5 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/base/power/runtime-test.c b/drivers/base/power/runtime-test.c
> index 263c28d5fc50..1be18e871f1d 100644
> --- a/drivers/base/power/runtime-test.c
> +++ b/drivers/base/power/runtime-test.c
> @@ -43,15 +43,11 @@ static void pm_runtime_already_suspended_test(struct kunit *test)
>  	KUNIT_EXPECT_EQ(test, 0, pm_runtime_barrier(dev)); /* no wakeup needed */
>  
>  	KUNIT_EXPECT_TRUE(test, pm_runtime_suspended(dev));
> -	/*
> -	 * We never actually left RPM_SUSPENDED, but rpm_idle() still treats
> -	 * this as -EAGAIN / "runtime PM status change ongoing".
> -	 */
> -	KUNIT_EXPECT_EQ(test, -EAGAIN, pm_runtime_put(dev));
> +	KUNIT_EXPECT_EQ(test, 1, pm_runtime_put(dev));
>  
>  	pm_runtime_get_noresume(dev);
>  	KUNIT_EXPECT_TRUE(test, pm_runtime_suspended(dev));
> -	KUNIT_EXPECT_EQ(test, -EAGAIN, pm_runtime_put_sync(dev));
> +	KUNIT_EXPECT_EQ(test, 1, pm_runtime_put_sync(dev));
>  
>  	KUNIT_EXPECT_EQ(test, 1, pm_runtime_suspend(dev));
>  	KUNIT_EXPECT_EQ(test, 1, pm_runtime_autosuspend(dev));
> diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
> index 3e84dc4122de..17cf111d16aa 100644
> --- a/drivers/base/power/runtime.c
> +++ b/drivers/base/power/runtime.c
> @@ -498,6 +498,9 @@ static int rpm_idle(struct device *dev, int rpmflags)
>  	if (retval < 0)
>  		;	/* Conditions are wrong. */
>  
> +	else if ((rpmflags & RPM_GET_PUT) && (retval == 1))
> +		;	/* put() is allowed in RPM_SUSPENDED */
> +

No objections from my side,
Reviewed-by: Dhruva Gole <d-gole@...com>

-- 
Best regards,
Dhruva Gole
Texas Instruments Incorporated