linux-kernel - Re: [PATCH v1] PM: runtime: docs: Update pm_runtime

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Message-ID: <aPlCJB3nzSbpO-S2@google.com>
Date: Wed, 22 Oct 2025 13:44:20 -0700
From: Brian Norris <briannorris@...omium.org>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: Linux PM <linux-pm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Lukas Wunner <lukas@...ner.de>,
	Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Subject: Re: [PATCH v1] PM: runtime: docs: Update pm_runtime_allow/forbid()
 documentation

Hi Rafael,

On Wed, Oct 22, 2025 at 10:26:23PM +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> Drop confusing descriptions of pm_runtime_allow() and pm_runtime_forbid()
> from Documentation/power/runtime_pm.rst and update the kerneldoc comments
> of these functions to better explain their purpose.
> 
> Link: https://lore.kernel.org/linux-pm/08976178-298f-79d9-1d63-cff5a4e56cc3@linux.intel.com/
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>  Documentation/power/runtime_pm.rst |   10 ----------
>  drivers/base/power/runtime.c       |   17 +++++++++++++----
>  2 files changed, 13 insertions(+), 14 deletions(-)
> 
> --- a/Documentation/power/runtime_pm.rst
> +++ b/Documentation/power/runtime_pm.rst
> @@ -480,16 +480,6 @@ drivers/base/power/runtime.c and include
>    `bool pm_runtime_status_suspended(struct device *dev);`
>      - return true if the device's runtime PM status is 'suspended'
>  
> -  `void pm_runtime_allow(struct device *dev);`
> -    - set the power.runtime_auto flag for the device and decrease its usage
> -      counter (used by the /sys/devices/.../power/control interface to
> -      effectively allow the device to be power managed at run time)
> -
> -  `void pm_runtime_forbid(struct device *dev);`
> -    - unset the power.runtime_auto flag for the device and increase its usage
> -      counter (used by the /sys/devices/.../power/control interface to
> -      effectively prevent the device from being power managed at run time)
> -

It feels a little odd just to strip 2 of the APIs from this doc, while
the rest remain. I'm not too familiar with ReST, nor with kerneldoc
integration, but would something like this work as a replacement?

.. kernel-doc:: drivers/base/power/runtime.c
   :export:

.. kernel-doc:: include/linux/pm_runtime.h

>    `void pm_runtime_no_callbacks(struct device *dev);`
>      - set the power.no_callbacks flag for the device and remove the runtime
>        PM attributes from /sys/devices/.../power (or prevent them from being
> --- a/drivers/base/power/runtime.c
> +++ b/drivers/base/power/runtime.c
> @@ -1664,9 +1664,12 @@ EXPORT_SYMBOL_GPL(devm_pm_runtime_get_no
>   * pm_runtime_forbid - Block runtime PM of a device.
>   * @dev: Device to handle.
>   *
> - * Increase the device's usage count and clear its power.runtime_auto flag,
> - * so that it cannot be suspended at run time until pm_runtime_allow() is called
> - * for it.
> + * Resume @dev if already suspended and block runtime suspend of @dev in such
> + * a way that it can be unblocked via the /sys/devices/.../power/control
> + * interface, or otherwise by calling pm_runtime_allow().
> + *
> + * Calling this function many times in a row has the same effect as calling it
> + * once.
>   */
>  void pm_runtime_forbid(struct device *dev)
>  {
> @@ -1687,7 +1690,13 @@ EXPORT_SYMBOL_GPL(pm_runtime_forbid);
>   * pm_runtime_allow - Unblock runtime PM of a device.
>   * @dev: Device to handle.
>   *
> - * Decrease the device's usage count and set its power.runtime_auto flag.
> + * Unblock runtime suspend of @dev after it has been blocked by
> + * pm_runtime_forbid() (for instance, if it has been blocked via the
> + * /sys/devices/.../power/control interface), check if @dev can be
> + * suspended and suspend it in that case.
> + *
> + * Calling this function many times in a row has the same effect as calling it
> + * once.
>   */
>  void pm_runtime_allow(struct device *dev)
>  {

The rewording looks helpful, as it's much more API-user-oriented now. So
this looks good to me as-is, even if there are other potential
improvements to make:

Reviewed-by: Brian Norris <briannorris@...omium.org>

Thanks!