linux-kernel - [PATCH v1 10/10] PM: runtime: Discover the lack of runtime PM support

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Message-ID: <2511990.jE0xQCEvom@rjwysocki.net>
Date: Tue, 11 Feb 2025 22:25:29 +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 10/10] PM: runtime: Discover the lack of runtime PM support

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

Previous changes have updated the PM core to special-case devices that
have never had runtime PM enabled in some places, but what if a device
had had runtime PM enabled at one point, but then it was permanently
disabled?  Arguably, there is not much of a difference between such
devices and the devices that have never had runtime PM enabled as far
as system-wide suspend and resume is concerned, so they should be
handled in the same way.

For this reason, add a mechanism for discovering "lost" runtime PM
support in devices with the help of the power.last_status field used
for saving the last runtime PM status of the device known at the time
when runtime PM was disabled for it.

That field is set to RPM_INVALID initially and whenever runtime PM is
enabled for a device (that is, when its power.disable_depth counter
drops down to zero) and it is set to the current runtime PM status of
the device when runtime PM is disabled (that is, the power.disable_depth
counter becomes nonzero).  Therefore, if power.last_status is equal to
RPM_INVALID for a device with runtime PM disabled, it means that
runtime PM has never been enabled for that device.

The PM core will now change the power.last_status value to RPM_UNKNOWN
for devices having runtime PM disabled and power.last_status different
from RPM_INVALID during the "prepare" phase of system suspend.  Then,
__pm_runtime_disable() called subsequently on the device will set
power.last_status to RPM_INVALID unless it changes from RPM_UNKNOWN
to some other value in the meantime which requires enabling runtime PM
for the device.  When power.last_status becomes RPM_INVALID and runtime
PM is still disabled, the device will be handled as a "no runtime PM
support" one from that point on until runtime PM is enabled for it
again.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
 drivers/base/power/main.c    |    6 ++++++
 drivers/base/power/runtime.c |   25 +++++++++++++++++++++++++
 include/linux/pm.h           |    1 +
 include/linux/pm_runtime.h   |    2 ++
 4 files changed, 34 insertions(+)

--- a/drivers/base/power/main.c
+++ b/drivers/base/power/main.c
@@ -1817,6 +1817,12 @@
 	 * it again during the complete phase.
 	 */
 	pm_runtime_get_noresume(dev);
+	/*
+	 * Devices that have had runtime PM disabled recently may need to be
+	 * handled as though they have never supported it, so arrange for
+	 * detecting that situation.
+	 */
+	pm_runtime_kick_last_status(dev);
 
 	if (dev->power.syscore)
 		return 0;
--- a/drivers/base/power/runtime.c
+++ b/drivers/base/power/runtime.c
@@ -1480,6 +1480,9 @@
 
 	if (dev->power.disable_depth > 0) {
 		dev->power.disable_depth++;
+		if (dev->power.last_status == RPM_UNKNOWN)
+			dev->power.last_status = RPM_INVALID;
+
 		goto out;
 	}
 
@@ -1568,6 +1571,28 @@
 EXPORT_SYMBOL_GPL(devm_pm_runtime_enable);
 
 /**
+ * pm_runtime_kick_last_status - Start runtime PM support verification.
+ * @dev: Target device.
+ *
+ * If runtime PM is currently disabled for @dev, but it has been enabled at one
+ * point, change power.last_status for it to RPM_UNKNOWN, and if it is still
+ * RPM_UNKNOWN when __pm_runtime_disabled() is called for @dev next time, it
+ * will be changed to RPM_INVALID indicating no runtime PM support going
+ * forward until pm_runtime_enable() is called for @dev.
+ *
+ * This function is used by the PM core.
+ */
+void pm_runtime_kick_last_status(struct device *dev)
+{
+	spin_lock_irq(&dev->power.lock);
+
+	if (dev->power.disable_depth && dev->power.last_status != RPM_INVALID)
+		dev->power.last_status = RPM_UNKNOWN;
+
+	spin_unlock_irq(&dev->power.lock);
+}
+
+/**
  * pm_runtime_forbid - Block runtime PM of a device.
  * @dev: Device to handle.
  *
--- a/include/linux/pm.h
+++ b/include/linux/pm.h
@@ -597,6 +597,7 @@
 	RPM_RESUMING,
 	RPM_SUSPENDED,
 	RPM_SUSPENDING,
+	RPM_UNKNOWN,
 };
 
 /*
--- a/include/linux/pm_runtime.h
+++ b/include/linux/pm_runtime.h
@@ -80,6 +80,7 @@
 extern int pm_runtime_barrier(struct device *dev);
 extern void pm_runtime_enable(struct device *dev);
 extern void __pm_runtime_disable(struct device *dev, bool check_resume);
+extern void pm_runtime_kick_last_status(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);
@@ -288,6 +289,7 @@
 static inline int pm_runtime_barrier(struct device *dev) { return 0; }
 static inline void pm_runtime_enable(struct device *dev) {}
 static inline void __pm_runtime_disable(struct device *dev, bool c) {}
+static inline void pm_runtime_kick_last_status(struct device *dev) {}
 static inline void pm_runtime_allow(struct device *dev) {}
 static inline void pm_runtime_forbid(struct device *dev) {}