linux-kernel - [PATCH] PM: add kernel parameter to disable asynchronous suspend/resume

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Message-Id: <20250708-pm-async-off-v1-1-1b200cc03d9c@linaro.org>
Date: Tue, 08 Jul 2025 14:28:35 +0000
From: Tudor Ambarus <tudor.ambarus@...aro.org>
To: Jonathan Corbet <corbet@....net>, 
 "Rafael J. Wysocki" <rafael@...nel.org>, Pavel Machek <pavel@...nel.org>, 
 Len Brown <len.brown@...el.com>
Cc: linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-pm@...r.kernel.org, peter.griffin@...aro.org, 
 andre.draszik@...aro.org, willmcvicker@...gle.com, kernel-team@...roid.com, 
 Tudor Ambarus <tudor.ambarus@...aro.org>
Subject: [PATCH] PM: add kernel parameter to disable asynchronous
 suspend/resume

On some platforms, device dependencies are not properly represented by
device links, which can cause issues when asynchronous power management
is enabled. While it is possible to disable this via sysfs, doing so
at runtime can race with the first system suspend event.

This patch introduces a kernel command-line parameter, "pm_async", which
can be set to "off" to globally disable asynchronous suspend and resume
operations from early boot. This provides a robust way to fall back to
synchronous (sequential) operation, which can stabilize platforms with
problematic dependencies and also serve as a useful debugging tool.

The default behavior remains unchanged (asynchronous enabled). To disable
it, boot the kernel with the "pm_async=off" parameter.

Signed-off-by: Tudor Ambarus <tudor.ambarus@...aro.org>
---
Dealing with the pixel6 downstream drivers to cope with the changes from
https://lore.kernel.org/linux-pm/10629535.nUPlyArG6x@rjwysocki.net/.

Similar to what people already reported it seems pixel6 lacks proper
device links dependencies downstream causing i2c and spi client drivers
to fail to suspend. Add kernel param to disable async suspend/resume.
---
 Documentation/admin-guide/kernel-parameters.txt | 9 +++++++++
 kernel/power/main.c                             | 9 +++++++++
 2 files changed, 18 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index f1f2c0874da9ddfc95058c464fdf5dabaf0de713..55ba3e747d86c09a0696e105a1d9cd99218f0c07 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5000,6 +5000,15 @@
 			that number, otherwise (e.g., 'pmu_override=on'), MMCR1
 			remains 0.

+	pm_async	[PM]
+			If set to "off", disables asynchronous suspend and
+			resume of devices during system-wide power transitions.
+			This can be useful on platforms where device
+			dependencies are not well-defined, or for debugging
+			power management issues. Defaults to "on" (asynchronous
+			operations enabled).
+
+
 	pm_debug_messages	[SUSPEND,KNL]
 			Enable suspend/resume debug messages during boot up.

diff --git a/kernel/power/main.c b/kernel/power/main.c
index 3d484630505ae91fea29f7f9b3fbcf7e585955d8..3cf2d7e72567ecbea2cd80acd3c7f6da85f5bef4 100644
--- a/kernel/power/main.c
+++ b/kernel/power/main.c
@@ -8,6 +8,7 @@

 #include <linux/acpi.h>
 #include <linux/export.h>
+#include <linux/init.h>
 #include <linux/kobject.h>
 #include <linux/string.h>
 #include <linux/pm-trace.h>
@@ -112,6 +113,14 @@ int pm_notifier_call_chain(unsigned long val)
 /* If set, devices may be suspended and resumed asynchronously. */
 int pm_async_enabled = 1;

+static int __init pm_async_setup(char *str)
+{
+	if (!strcmp(str, "off"))
+		pm_async_enabled = 0;
+	return 1;
+}
+__setup("pm_async=", pm_async_setup);
+
 static ssize_t pm_async_show(struct kobject *kobj, struct kobj_attribute *attr,
 			     char *buf)
 {

---
base-commit: d7b8f8e20813f0179d8ef519541a3527e7661d3a
change-id: 20250708-pm-async-off-bf2a3e2a27ef

Best regards,
-- 
Tudor Ambarus <tudor.ambarus@...aro.org>