linux-kernel - Re: [PATCH v5 1/2] pm: runtime: Add new devm functions

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Message-ID: <d926d2c2-8cc9-4a71-b8ca-b5f03ac9afb8@prolan.hu>
Date: Thu, 27 Mar 2025 14:24:28 +0100
From: Csókás Bence <csokas.bence@...lan.hu>
To: "Rafael J. Wysocki" <rafael@...nel.org>
CC: <linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>, "Varshini
 Rajendran" <varshini.rajendran@...rochip.com>, Tudor Ambarus
	<tudor.ambarus@...aro.org>, Mark Brown <broonie@...nel.org>,
	<linux-spi@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>, "Len
 Brown" <len.brown@...el.com>, Pavel Machek <pavel@....cz>, Greg Kroah-Hartman
	<gregkh@...uxfoundation.org>, Danilo Krummrich <dakr@...nel.org>, "Alexander
 Dahl" <ada@...rsis.com>, Nicolas Ferre <nicolas.ferre@...rochip.com>,
	Alexandre Belloni <alexandre.belloni@...tlin.com>, Claudiu Beznea
	<claudiu.beznea@...on.dev>, Pavel Machek <pavel@...nel.org>
Subject: Re: [PATCH v5 1/2] pm: runtime: Add new devm functions

Hi,

On 2025. 03. 27. 12:08, Rafael J. Wysocki wrote:
>>> Now, there is a reason why calling pm_runtime_set_suspended() on a
>>> device after disabling runtime PM for it is a good idea at all.
>>> Namely, disabling runtime PM alone does not release the device's
>>> suppliers or its parent, so if you want to release them after
>>> disabling runtime PM for the device, you need to do something more.
>>> I'm thinking that this is a  mistake in the design of the runtime PM
>>> core.
>>
>> Well, this is the order in which the original driver worked before
>> anyways. As a quick fix, would it work if we created a devm function
>> that would pm_runtime_set_active(), immediately followed by
>> pm_runtime_enable(), and on cleanup it would pm_runtime_set_suspended()
>> followed by pm_runtime_disable_action() (i.e.
>> pm_runtime_dont_use_autosuspend() and pm_runtime_disable())?
> 
> On cleanup you'd need to ensure that pm_runtime_disable() is followed
> by pm_runtime_set_suspended() (not the other way around).  Also
> pm_runtime_dont_use_autosuspend() needs to be called when runtime PM
> is still enabled.
> 
> With the above taken into account, it would work.

Ok, so which is the correct order then?

1. the way it is done now in [PATCH v5 2/2] (which is the same order the 
driver has been using before anyways):

     pm_runtime_use_autosuspend()
/-- devm_pm_runtime_set_active()
|   /-- devm_pm_runtime_enable()
|   |   /-- devm_pm_runtime_get_noresume()
|   |   |
|   |   \-> pm_runtime_put_noidle()
|   \-> pm_runtime_dont_use_autosuspend() &&
|       pm_runtime_disable()
\-> pm_runtime_set_suspended()

or,
2. swapped set_suspended() and runtime_disable()

     pm_runtime_use_autosuspend()
/-- devm_pm_runtime_set_active_enabled() [new fn]
|    == pm_runtime_set_active() &&
|       pm_runtime_enable()
|   /-- devm_pm_runtime_get_noresume()
|   |
|   \-> pm_runtime_put_noidle()
\--> pm_runtime_set_suspended()
      pm_runtime_dont_use_autosuspend()
      pm_runtime_disable()

Bence