[PATCH v3 2/3] PM: dpm_watchdog: Allow disabling DPM watchdog by default

[Tzung-Bi Shih <tzungbi@kernel.org>]

Introduce the CONFIG_DPM_WATCHDOG_DEFAULT_ENABLED Kconfig option to
allow the device suspend/resume watchdog (DPM watchdog) to be disabled
by default at compile time.

Additionally, introduce the "dpm_watchdog_enabled" module parameter to
allow the watchdog to be enabled or disabled at boot time (via
"power.dpm_watchdog_enabled") and at runtime (via sysfs).

This provides flexibility for systems that want the watchdog code
compiled in but inactive by default, allowing it to be enabled only when
needed.

Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
---
v3:
- Add "PM" tag (was missing).
- Update the format and specify dependencies in kernel-parameters.txt.
- Update the help message in Kconfig to reflect that dpm_watchdog_enabled
  can be set at runtime as well.

v2: https://lore.kernel.org/all/20260604090756.2884671-3-tzungbi@kernel.org
- Use module parameter and bool for dpm_watchdog_enabled.
- Use IS_ENABLED().

v1: https://lore.kernel.org/all/20260528103215.505795-1-tzungbi@kernel.org

 Documentation/admin-guide/kernel-parameters.txt |  8 ++++++++
 drivers/base/power/main.c                       | 11 +++++++++++
 kernel/power/Kconfig                            | 10 ++++++++++
 3 files changed, 29 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 00375193bd26..f2620764c28e 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -47,6 +47,7 @@
 	PCI	PCI bus support is enabled.
 	PCIE	PCI Express support is enabled.
 	PCMCIA	The PCMCIA subsystem is enabled.
+	PM	Power Management support is enabled.
 	PNP	Plug & Play support is enabled.
 	PPC	PowerPC architecture is enabled.
 	PPT	Parallel port support is enabled.
@@ -5399,6 +5400,13 @@ Kernel parameters
 			function to NULL. On Idle the CPU just reduces
 			execution priority.
 
+	power.dpm_watchdog_enabled=
+			[PM] Enable or disable the device suspend/resume
+			watchdog (DPM watchdog).  Requires CONFIG_PM_SLEEP and
+			CONFIG_DPM_WATCHDOG enabled.
+			Format: <bool>
+			Default value is set by CONFIG_DPM_WATCHDOG_DEFAULT_ENABLED.
+
 	ppc_strict_facility_enable
 			[PPC,ENABLE] This option catches any kernel floating point,
 			Altivec, VSX and SPE outside of regions specifically
diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
index cd864f3a2799..7822c29b7c8d 100644
--- a/drivers/base/power/main.c
+++ b/drivers/base/power/main.c
@@ -534,6 +534,11 @@ module_param(dpm_watchdog_all_cpu_backtrace, bool, 0644);
 MODULE_PARM_DESC(dpm_watchdog_all_cpu_backtrace,
 		 "Backtrace all CPUs on DPM watchdog timeout");
 
+static bool __read_mostly dpm_watchdog_enabled =
+				IS_ENABLED(CONFIG_DPM_WATCHDOG_DEFAULT_ENABLED);
+module_param(dpm_watchdog_enabled, bool, 0644);
+MODULE_PARM_DESC(dpm_watchdog_enabled, "Enable DPM watchdog");
+
 /**
  * dpm_watchdog_handler - Driver suspend / resume watchdog handler.
  * @t: The timer that PM watchdog depends on.
@@ -577,6 +582,9 @@ static void dpm_watchdog_set(struct dpm_watchdog *wd, struct device *dev)
 {
 	struct timer_list *timer = &wd->timer;
 
+	if (!dpm_watchdog_enabled)
+		return;
+
 	wd->dev = dev;
 	wd->tsk = current;
 	wd->fatal = CONFIG_DPM_WATCHDOG_TIMEOUT == CONFIG_DPM_WATCHDOG_WARNING_TIMEOUT;
@@ -595,6 +603,9 @@ static void dpm_watchdog_clear(struct dpm_watchdog *wd)
 {
 	struct timer_list *timer = &wd->timer;
 
+	if (!dpm_watchdog_enabled)
+		return;
+
 	timer_delete_sync(timer);
 	timer_destroy_on_stack(timer);
 }
diff --git a/kernel/power/Kconfig b/kernel/power/Kconfig
index 530c897311d4..b16bd159074a 100644
--- a/kernel/power/Kconfig
+++ b/kernel/power/Kconfig
@@ -268,6 +268,16 @@ config DPM_WATCHDOG
 	  captured in pstore device for inspection in subsequent
 	  boot session.
 
+config DPM_WATCHDOG_DEFAULT_ENABLED
+	bool "Enable DPM watchdog by default"
+	depends on DPM_WATCHDOG
+	default y
+	help
+	  If you say Y here, the DPM watchdog will be enabled by default.
+	  If you say N, it will be compiled in but disabled.  It can be
+	  enabled at boot time via the "power.dpm_watchdog_enabled" kernel
+	  parameter or at runtime via sysfs.
+
 config DPM_WATCHDOG_TIMEOUT
 	int "Watchdog timeout to panic in seconds"
 	range 1 120
-- 
2.54.0.1099.g489fc7bff1-goog