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

[Rafael J. Wysocki]

On Mon, Jun 8, 2026 at 4:16 AM Tzung-Bi Shih <tzungbi@xxxxxxxxxx> wrote:
>
> 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).

I think that the new module param is more important because the new
config option is just its default value, so I'd rearrange the
changelog.

Also, I think that the "DEFAULT_" part of the new config option name
doesn't provide any additional value, so I'd just drop it.

> 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@xxxxxxxxxx>
> ---
> 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@xxxxxxxxxx
> - Use module parameter and bool for dpm_watchdog_enabled.
> - Use IS_ENABLED().
>
> v1: https://lore.kernel.org/all/20260528103215.505795-1-tzungbi@xxxxxxxxxx
>
>  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
>