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SubjectRe: [PATCH v2] PM: runtime: document common mistake with pm_runtime_get_sync()
On Wed, May 26, 2021 at 6:23 PM Krzysztof Kozlowski
<krzysztof.kozlowski@canonical.com> wrote:
>
> pm_runtime_get_sync(), contradictory to intuition, does not drop the
> runtime PM usage counter on errors which lead to several wrong usages in
> drivers (missing the put). pm_runtime_resume_and_get() was added as a
> better implementation so document the preference of using it, hoping it
> will stop bad patterns.
>
> Suggested-by: Marek Szyprowski <m.szyprowski@samsung.com>
> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
>
> ---
>
> Changes since v1:
> 1. Reword after comments from Rafael.
> ---
> Documentation/power/runtime_pm.rst | 6 +++++-
> include/linux/pm_runtime.h | 3 +++
> 2 files changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/power/runtime_pm.rst b/Documentation/power/runtime_pm.rst
> index 18ae21bf7f92..33619bf83f69 100644
> --- a/Documentation/power/runtime_pm.rst
> +++ b/Documentation/power/runtime_pm.rst
> @@ -378,7 +378,11 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h:
>
> `int pm_runtime_get_sync(struct device *dev);`
> - increment the device's usage counter, run pm_runtime_resume(dev) and
> - return its result
> + return its result;
> + be aware that it does not drop the device's usage counter on errors so
> + so consider using pm_runtime_resume_and_get() instead of it, especially
> + if its return value is checked by the caller, as this is likely to result
> + in cleaner code.
>
> `int pm_runtime_get_if_in_use(struct device *dev);`
> - return -EINVAL if 'power.disable_depth' is nonzero; otherwise, if the
> diff --git a/include/linux/pm_runtime.h b/include/linux/pm_runtime.h
> index 6c08a085367b..aab8b35e9f8a 100644
> --- a/include/linux/pm_runtime.h
> +++ b/include/linux/pm_runtime.h
> @@ -380,6 +380,9 @@ static inline int pm_runtime_get(struct device *dev)
> * The possible return values of this function are the same as for
> * pm_runtime_resume() and the runtime PM usage counter of @dev remains
> * incremented in all cases, even if it returns an error code.
> + * Consider using pm_runtime_resume_and_get() instead of it, especially
> + * if its return value is checked by the caller, as this is likely to result
> + * in cleaner code.
> */
> static inline int pm_runtime_get_sync(struct device *dev)
> {
> --

Applied as 5.14 material (with some cosmetic edits), thanks!

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