linux-kernel - [PATCH v1 2/3] PM: runtime: Convert pm_runtime

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Message-ID: <1923449.tdWV9SEqCh@rjwysocki.net>
Date: Thu, 27 Feb 2025 11:47:33 +0100
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Linux PM <linux-pm@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
 Alan Stern <stern@...land.harvard.edu>, Ulf Hansson <ulf.hansson@...aro.org>,
 Johan Hovold <johan@...nel.org>,
 Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
 Jon Hunter <jonathanh@...dia.com>
Subject:
 [PATCH v1 2/3] PM: runtime: Convert pm_runtime_blocked() to static inline

From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

The comment in pm_runtime_blocked() is acutally wrong: power.last_status
is not a bit field.  Its data type is an enum and so one can reasonably
assume that partial updates of it will not be observed.

Accordingly, pm_runtime_blocked() can be converted to a static inline
function and the related locking overhead can be eliminated, so long
as it is only used in system suspend/resume code paths because
power.last_status is not expected to be updated concurrently while
that code is running.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
 drivers/base/power/runtime.c |   17 -----------------
 include/linux/pm_runtime.h   |   12 +++++++++++-
 2 files changed, 11 insertions(+), 18 deletions(-)

--- a/drivers/base/power/runtime.c
+++ b/drivers/base/power/runtime.c
@@ -1560,23 +1560,6 @@
 }
 EXPORT_SYMBOL_GPL(pm_runtime_enable);

-bool pm_runtime_blocked(struct device *dev)
-{
-	bool ret;
-
-	/*
-	 * dev->power.last_status is a bit field, so in case it is updated via
-	 * RMW, read it under the spin lock.
-	 */
-	spin_lock_irq(&dev->power.lock);
-
-	ret = dev->power.last_status == RPM_BLOCKED;
-
-	spin_unlock_irq(&dev->power.lock);
-
-	return ret;
-}
-
 static void pm_runtime_disable_action(void *data)
 {
 	pm_runtime_dont_use_autosuspend(data);
--- a/include/linux/pm_runtime.h
+++ b/include/linux/pm_runtime.h
@@ -81,7 +81,6 @@
 extern void pm_runtime_unblock(struct device *dev);
 extern void pm_runtime_enable(struct device *dev);
 extern void __pm_runtime_disable(struct device *dev, bool check_resume);
-extern bool pm_runtime_blocked(struct device *dev);
 extern void pm_runtime_allow(struct device *dev);
 extern void pm_runtime_forbid(struct device *dev);
 extern void pm_runtime_no_callbacks(struct device *dev);
@@ -200,6 +199,17 @@
 }

 /**
+ * pm_runtime_blocked - Check if runtime PM enabling is blocked.
+ * @dev: Target device.
+ *
+ * Do not call this function outside system suspend/resume code paths.
+ */
+static inline bool pm_runtime_blocked(struct device *dev)
+{
+	return dev->power.last_status == RPM_BLOCKED;
+}
+
+/**
  * pm_runtime_has_no_callbacks - Check if runtime PM callbacks may be present.
  * @dev: Target device.
  *