Re: [PATCH V3 2/6] PM: runtime: Add pm_runtime_if_active guard and conditional variant

On Mon, Aug 10, 2026 at 12:11 PM Golla Nagendra <[email protected]> wrote:
>
> Add a pm_runtime_if_active base guard and its _try conditional variant
> to pm_runtime.h for drivers that need to conditionally acquire a runtime
> PM reference only when the device is already active.
>
> The base guard must not be used directly via guard()/scoped_guard()
> because pm_runtime_get_if_active() only acquires a reference when it
> returns 1; the destructor unconditionally calls pm_runtime_put(), which
> would underflow usage_count on a suspended or RPM-disabled device. The
> base guard exists solely to back the DEFINE_GUARD_COND _try variant.

Which is not nice and confusing IMV.

Is there anything like that anywhere else in the kernel?

> The _try variant (used via PM_RUNTIME_ACQUIRE_IF_ACTIVE) checks the
> return value and only runs the destructor when the reference was
> actually acquired. This is useful in interrupt handlers where the
> device may be runtime-suspended and MMIO accesses must be avoided.
>
> Signed-off-by: Golla Nagendra <[email protected]>
> ---
> Changes in V3:
> - New patch: add PM_RUNTIME_ACQUIRE_IF_ACTIVE() guard and backing
>   infrastructure to pm_runtime.h so that drivers
>   can use a structured guard instead of an open-coded
>   pm_runtime_get_if_active()/pm_runtime_put() pair
> ---
>  include/linux/pm_runtime.h | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/include/linux/pm_runtime.h b/include/linux/pm_runtime.h
> index 64921b10ac74..bc6de97e6111 100644
> --- a/include/linux/pm_runtime.h
> +++ b/include/linux/pm_runtime.h
> @@ -609,6 +609,13 @@ DEFINE_GUARD(pm_runtime_active, struct device *,
>              pm_runtime_get_sync(_T), pm_runtime_put(_T));
>  DEFINE_GUARD(pm_runtime_active_auto, struct device *,
>              pm_runtime_get_sync(_T), pm_runtime_put_autosuspend(_T));
> +/*
> + * Do not use directly -- the destructor calls pm_runtime_put()
> + * unconditionally, which underflows if no reference was acquired.
> + * Use only via the _try variant below.
> + */
> +DEFINE_GUARD(pm_runtime_if_active, struct device *,
> +            pm_runtime_get_if_active(_T), pm_runtime_put(_T));
>  /*
>   * Use the following guards with ACQUIRE()/ACQUIRE_ERR().
>   *
> @@ -624,6 +631,8 @@ DEFINE_GUARD_COND(pm_runtime_active_auto, _try,
>                   pm_runtime_get_active(_T, RPM_TRANSPARENT), _RET == 0)
>  DEFINE_GUARD_COND(pm_runtime_active_auto, _try_enabled,
>                   pm_runtime_resume_and_get(_T), _RET == 0)
> +DEFINE_GUARD_COND(pm_runtime_if_active, _try,
> +                 pm_runtime_get_if_active(_T) ?: -EAGAIN, _RET == 1)
>
>  /* ACQUIRE() wrapper macros for the guards defined above. */
>
> @@ -639,6 +648,9 @@ DEFINE_GUARD_COND(pm_runtime_active_auto, _try_enabled,
>  #define PM_RUNTIME_ACQUIRE_IF_ENABLED_AUTOSUSPEND(_dev, _var)  \
>         ACQUIRE(pm_runtime_active_auto_try_enabled, _var)(_dev)
>
> +#define PM_RUNTIME_ACQUIRE_IF_ACTIVE(_dev, _var)       \
> +       ACQUIRE(pm_runtime_if_active_try, _var)(_dev)
> +
>  /*
>   * ACQUIRE_ERR() wrapper macro for guard pm_runtime_active.
>   *
> --
> 2.43.7
>