linux-kernel - [PATCH v1 1/3] PM: sleep: Update power.smart

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Message-ID: <2368159.ElGaqSPkdT@rjwysocki.net>
Date: Thu, 27 Feb 2025 11:45:52 +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 1/3] PM: sleep: Update power.smart_suspend under PM spinlock

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

Put the update of the power.smart_suspend device flag under the PM
spinlock of the device in case multiple bit fields in struct dev_pm_info
occupy one memory location which needs to be updated via RMW every time
any of these bit fields is updated.

The lock in question is already held around the power.direct_complete
flag update in device_prepare() for the same reason, so this change does
not add locking-related overhead to the code.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
 drivers/base/power/main.c |   35 +++++++++++++++++++----------------
 1 file changed, 19 insertions(+), 16 deletions(-)

--- a/drivers/base/power/main.c
+++ b/drivers/base/power/main.c
@@ -1789,9 +1789,10 @@
 	return error;
 }
 
-static void device_prepare_smart_suspend(struct device *dev)
+static bool device_prepare_smart_suspend(struct device *dev)
 {
 	struct device_link *link;
+	bool ret = true;
 	int idx;
 
 	/*
@@ -1802,17 +1803,13 @@
 	 * or any of its suppliers that take runtime PM into account, it cannot
 	 * be enabled for the device either.
 	 */
-	dev->power.smart_suspend = dev->power.no_pm_callbacks ||
-		dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_SUSPEND);
-
-	if (!dev_pm_smart_suspend(dev))
-		return;
+	if (!dev->power.no_pm_callbacks &&
+	    !dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_SUSPEND))
+		return false;
 
 	if (dev->parent && !dev_pm_smart_suspend(dev->parent) &&
-	    !dev->parent->power.ignore_children && !pm_runtime_blocked(dev->parent)) {
-		dev->power.smart_suspend = false;
-		return;
-	}
+	    !dev->parent->power.ignore_children && !pm_runtime_blocked(dev->parent))
+		return false;
 
 	idx = device_links_read_lock();
 
@@ -1822,12 +1819,14 @@
 
 		if (!dev_pm_smart_suspend(link->supplier) &&
 		    !pm_runtime_blocked(link->supplier)) {
-			dev->power.smart_suspend = false;
+			ret = false;
 			break;
 		}
 	}
 
 	device_links_read_unlock(idx);
+
+	return ret;
 }
 
 /**
@@ -1841,7 +1840,7 @@
 static int device_prepare(struct device *dev, pm_message_t state)
 {
 	int (*callback)(struct device *) = NULL;
-	bool no_runtime_pm;
+	bool smart_suspend;
 	int ret = 0;
 
 	/*
@@ -1857,7 +1856,7 @@
 	 * suspend-resume cycle is complete, so prepare to trigger a warning on
 	 * subsequent attempts to enable it.
 	 */
-	no_runtime_pm = pm_runtime_block_if_disabled(dev);
+	smart_suspend = !pm_runtime_block_if_disabled(dev);
 
 	if (dev->power.syscore)
 		return 0;
@@ -1893,9 +1892,12 @@
 		return ret;
 	}
 	/* Do not enable "smart suspend" for devices without runtime PM. */
-	if (!no_runtime_pm)
-		device_prepare_smart_suspend(dev);
+	if (smart_suspend)
+		smart_suspend = device_prepare_smart_suspend(dev);
+
+	spin_lock_irq(&dev->power.lock);
 
+	dev->power.smart_suspend = smart_suspend;
 	/*
 	 * A positive return value from ->prepare() means "this device appears
 	 * to be runtime-suspended and its state is fine, so if it really is
@@ -1903,11 +1905,12 @@
 	 * will do the same thing with all of its descendants".  This only
 	 * applies to suspend transitions, however.
 	 */
-	spin_lock_irq(&dev->power.lock);
 	dev->power.direct_complete = state.event == PM_EVENT_SUSPEND &&
 		(ret > 0 || dev->power.no_pm_callbacks) &&
 		!dev_pm_test_driver_flags(dev, DPM_FLAG_NO_DIRECT_COMPLETE);
+
 	spin_unlock_irq(&dev->power.lock);
+
 	return 0;
 }