PM: dpm_watchdog: Improve DPM watchdog configurability

This series improves the configurability of the DPM watchdog.

Currently, the DPM watchdog is always enabled if compiled in. Also, the module parameters defined in drivers/base/power/main.c use the generic and non-descriptive "main" prefix.

This series addresses these limitations.

Patch 1 renames the module parameter prefix for
drivers/base/power/main.c from "main" to "pm".

Patch 2 introduces the "dpm_watchdog_enabled" module parameter to allow enabling/disabling the watchdog at boot time and runtime. It also adds CONFIG_DPM_WATCHDOG_ENABLED to set the default value of the module parameter at compile time.

The primary motivation for this configurability revolves around Android GKI (Generic Kernel Image). We want to enable CONFIG_DPM_WATCHDOG in the GKI so the feature is available. However, because the GKI is shared across many different devices, we don't want to inadvertently affect devices that are unaware of this feature. This provides a way to compile it in, but keep it disabled by default for those devices via the kernel command line or module parameters.

To maintain backward compatibility, CONFIG_DPM_WATCHDOG_ENABLED relies on default y. Previously, the DPM watchdog was always active if CONFIG_DPM_WATCHDOG was set. Defaulting this new option to 'y' ensures that the behavior remains unchanged for existing users and defconfigs when they upgrade.
---
v6:
- Change the prefix "pm_sleep" -> "pm".

v5: https://lore.kernel.org/all/[email protected]
- Rebase to v7.2-rc1.
- Fix Signed-off-by lines.

v4: https://lore.kernel.org/all/[email protected]
- Address review comments.
- Patch 3 in v3 has applied separately.

v3: https://lore.kernel.org/all/[email protected]
- Address review comments on patch 2.

v2: https://lore.kernel.org/all/[email protected]
- Form a new series.

v1: Doesn't exist.

Tzung-Bi Shih (2):
PM: sleep: Rename module parameters prefix to "pm"
PM: dpm_watchdog: Allow disabling DPM watchdog by default

 Documentation/admin-guide/kernel-parameters.txt |  7 +++++++
 drivers/base/power/main.c                       | 14 ++++++++++++++
 kernel/power/Kconfig                            | 10 ++++++++++
 3 files changed, 31 insertions(+)

2.55.0.795.g602f6c329a-goog

Currently, the module parameters defined in drivers/base/power/main.c use the default prefix "main" (derived from the filename). The prefix is too generic and non-descriptive.

Redefine MODULE_PARAM_PREFIX to "pm." to group the module parameters under the namespace instead. This makes the parameters more descriptive.

---
v6:
- Change the prefix "pm_sleep" -> "pm".

v5: https://lore.kernel.org/all/[email protected]
- No changes.

v4: https://lore.kernel.org/all/[email protected]
- "power" -> "pm_sleep".

v3: https://lore.kernel.org/all/[email protected]
- No changes.

v2: https://lore.kernel.org/all/[email protected]
- New to the series.

v1: Doesn't exist.

---
 drivers/base/power/main.c | 3 +++
 1 file changed, 3 insertions(+)

index f71467f6ada4..49ea6e2cd735 100644
@@ -41,6 +41,9 @@
 #include "../base.h"
 #include "power.h"
 
+#undef MODULE_PARAM_PREFIX
+#define MODULE_PARAM_PREFIX "pm."
+
 typedef int (*pm_callback_t)(struct device *);
 
 /*

2.55.0.795.g602f6c329a-goog

Introduce the "dpm_watchdog_enabled" module parameter to allow the DPM watchdog to be enabled or disabled at boot time and runtime.

Additionally, introduce the CONFIG_DPM_WATCHDOG_ENABLED Kconfig option to set the default value of the module parameter at compile time.

The primary motivation for this configurability resolves around Android GKI (Generic Kernel Image). We want to enable CONFIG_DPM_WATCHDOG in the GKI so the feature is available. However, because the GKI is shared across many different devices, we don't want to inadvertently affect devices that are unaware of this feature. This provides a way to compile it in, but keep it disabled by default for those devices via the kernel command line or module parameters.

To maintain backward compatibility, CONFIG_DPM_WATCHDOG_ENABLED relies on default y. Previously, the DPM watchdog was always active if CONFIG_DPM_WATCHDOG was set. Defaulting this new option to 'y' ensures that the behavior remains unchanged for existing users and defconfigs when they upgrade.

---
v6:
- Change the prefix "pm_sleep" -> "pm".

v5: https://lore.kernel.org/all/[email protected]
- No changes.

v4: https://lore.kernel.org/all/[email protected]
- Rewrite the commit message to indicate the module parameter is the main change in the patch.
- DPM_WATCHDOG_DEFAULT_ENABLED -> DPM_WATCHDOG_ENABLED.

v3: https://lore.kernel.org/all/[email protected]
- 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/[email protected]
- Use module parameter and bool for dpm_watchdog_enabled.
- Use IS_ENABLED().

v1: https://lore.kernel.org/all/[email protected]

---
 Documentation/admin-guide/kernel-parameters.txt |  7 +++++++
 drivers/base/power/main.c                       | 11 +++++++++++
 kernel/power/Kconfig                            | 10 ++++++++++
 3 files changed, 28 insertions(+)

index b5493a7f8f22..ea0b70f87472 100644
@@ -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.

@@ -5354,6 +5355,12 @@ Kernel parameters
 	pm_debug_messages	[SUSPEND,KNL]
 			Enable suspend/resume debug messages during boot up.
 
+	pm.dpm_watchdog_enabled=
+			[PM] Enable or disable the DPM watchdog.  Requires
+			CONFIG_PM_SLEEP and CONFIG_DPM_WATCHDOG enabled.
+			Format: <bool>
+			Default value is set by CONFIG_DPM_WATCHDOG_ENABLED.
+
 	pnp.debug=1	[PNP]
 			Enable PNP debug messages (depends on the
 			CONFIG_PNP_DEBUG_MESSAGES option).  Change at run-time

index 49ea6e2cd735..184dc4b3b938 100644
@@ -535,6 +535,11 @@ 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_ENABLED);
+module_param(dpm_watchdog_enabled, bool, 0644);
+MODULE_PARM_DESC(dpm_watchdog_enabled, "Enable DPM watchdog");
+
 static unsigned int __read_mostly dpm_watchdog_timeout = CONFIG_DPM_WATCHDOG_TIMEOUT;
 static unsigned int __read_mostly dpm_watchdog_warning_timeout =
 						CONFIG_DPM_WATCHDOG_WARNING_TIMEOUT;

@@ -630,6 +635,9 @@ 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 = dpm_watchdog_timeout == dpm_watchdog_warning_timeout;

@@ -648,6 +656,9 @@ 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);
 }

index 530c897311d4..71165e7f04f4 100644
@@ -268,6 +268,16 @@ config DPM_WATCHDOG
 	  captured in pstore device for inspection in subsequent
 	  boot session.
 
+config DPM_WATCHDOG_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 "pm.dpm_watchdog_enabled" kernel
+	  parameter or at runtime via sysfs.
+
 config DPM_WATCHDOG_TIMEOUT
 	int "Watchdog timeout to panic in seconds"
 	range 1 120

2.55.0.795.g602f6c329a-goog

Since there was no further feedback on v5, I'm sending out v6. Any feedback would be appreciated.