linux-kernel - [PATCH v1] PM: runtime: Take active children into account in pm_runtime_get_if_in

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Message-ID: <12700973.O9o76ZdvQC@rjwysocki.net>
Date: Wed, 09 Jul 2025 12:41:45 +0200
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Linux PM <linux-pm@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
 Sakari Ailus <sakari.ailus@...ux.intel.com>, Alex Elder <elder@...aro.org>,
 Laurent Pinchart <laurent.pinchart@...asonboard.com>,
 Ulf Hansson <ulf.hansson@...aro.org>
Subject:
 [PATCH v1] PM: runtime: Take active children into account in
 pm_runtime_get_if_in_use()

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

For all practical purposes, there is no difference between the situation
in which a given device is not ignoring children and its active child
count is nonzero and the situation in which its runtime PM usage counter
is nonzero.  However, pm_runtime_get_if_in_use() will only increment the
device's usage counter and return 1 in the latter case.

For consistency, make it do so in the former case either by adjusting
pm_runtime_get_conditional() and update the related kerneldoc comments
accordingly.

Fixes: c0ef3df8dbae ("PM: runtime: Simplify pm_runtime_get_if_active() usage")
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
 drivers/base/power/runtime.c |   27 ++++++++++++++++++---------
 1 file changed, 18 insertions(+), 9 deletions(-)

--- a/drivers/base/power/runtime.c
+++ b/drivers/base/power/runtime.c
@@ -1203,10 +1203,12 @@
  *
  * Return -EINVAL if runtime PM is disabled for @dev.
  *
- * Otherwise, if the runtime PM status of @dev is %RPM_ACTIVE and either
- * @ign_usage_count is %true or the runtime PM usage counter of @dev is not
- * zero, increment the usage counter of @dev and return 1. Otherwise, return 0
- * without changing the usage counter.
+ * Otherwise, if its runtime PM status is %RPM_ACTIVE and (1) @ign_usage_count
+ * is set, or (2) @dev is not ignoring children and its active child count is
+ * nonero, or (3) the runtime PM usage counter of @dev is not zero, increment
+ * the usage counter of @dev and return 1.
+ *
+ * Otherwise, return 0 without changing the usage counter.
  *
  * If @ign_usage_count is %true, this function can be used to prevent suspending
  * the device when its runtime PM status is %RPM_ACTIVE.
@@ -1228,7 +1230,8 @@
 		retval = -EINVAL;
 	} else if (dev->power.runtime_status != RPM_ACTIVE) {
 		retval = 0;
-	} else if (ign_usage_count) {
+	} else if (ign_usage_count || (!dev->power.ignore_children &&
+		   atomic_read(&dev->power.child_count) > 0)) {
 		retval = 1;
 		atomic_inc(&dev->power.usage_count);
 	} else {
@@ -1261,10 +1264,16 @@
  * @dev: Target device.
  *
  * Increment the runtime PM usage counter of @dev if its runtime PM status is
- * %RPM_ACTIVE and its runtime PM usage counter is greater than 0, in which case
- * it returns 1. If the device is in a different state or its usage_count is 0,
- * 0 is returned. -EINVAL is returned if runtime PM is disabled for the device,
- * in which case also the usage_count will remain unmodified.
+ * %RPM_ACTIVE and its runtime PM usage counter is greater than 0 or it is not
+ * ignoring children and its active child count is nonzero.  1 is returned in
+ * this case.
+ *
+ * If @dev is in a different state or it is not in use (that is, its usage
+ * counter is 0, or it is ignoring children, or its active child count is 0),
+ * 0 is returned.
+ *
+ * -EINVAL is returned if runtime PM is disabled for the device, in which case
+ * also the usage counter of @dev is not updated.
  */
 int pm_runtime_get_if_in_use(struct device *dev)
 {