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[188.155.180.75]) by smtp.gmail.com with ESMTPSA id k22sm4825386wrh.5.2021.04.22.09.46.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 22 Apr 2021 09:46:25 -0700 (PDT) From: Krzysztof Kozlowski To: "Rafael J. Wysocki" , Len Brown , Pavel Machek , linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Krzysztof Kozlowski , Marek Szyprowski Subject: [PATCH] PM: runtime: document common mistake with pm_runtime_get_sync() Date: Thu, 22 Apr 2021 18:46:06 +0200 Message-Id: <20210422164606.68231-1-krzysztof.kozlowski@canonical.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org 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 Signed-off-by: Krzysztof Kozlowski --- Documentation/power/runtime_pm.rst | 4 +++- include/linux/pm_runtime.h | 3 +++ 2 files changed, 6 insertions(+), 1 deletion(-) diff --git a/Documentation/power/runtime_pm.rst b/Documentation/power/runtime_pm.rst index 18ae21bf7f92..478f08942811 100644 --- a/Documentation/power/runtime_pm.rst +++ b/Documentation/power/runtime_pm.rst @@ -378,7 +378,9 @@ 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 + usage of pm_runtime_resume_and_get(dev) usually results 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..0dfd23d2cfc3 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. + * Lack of decrementing the runtime PM usage counter on errors is a common + * mistake, so consider using pm_runtime_resume_and_get() instead for a cleaner + * code. */ static inline int pm_runtime_get_sync(struct device *dev) {