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SubjectRe: [linux-pm] [PATCH 3/5] PM: Support for system-wide power transitions in generic power domains
On Sun, 8 May 2011, Rafael J. Wysocki wrote:

> From: Rafael J. Wysocki <rjw@sisk.pl>
>
> Make generic power domains support system-wide power transitions
> (system suspend and hibernation). Add suspend, resume, freeze and
> thaw callbacks to be associated with struct generic_power_domain
> objects and make pm_genpd_init() use them as appropriate.

...

> Index: linux-2.6/drivers/base/power/domain.c
> ===================================================================
> --- linux-2.6.orig/drivers/base/power/domain.c
> +++ linux-2.6/drivers/base/power/domain.c
> @@ -273,6 +273,280 @@ static int pm_genpd_runtime_resume(struc
>
> #endif /* CONFIG_PM_RUNTIME */
>
> +#ifdef CONFIG_PM_SLEEP
> +
> +/**
> + * pm_genpd_powered_down - Check if power has been removed from a power domain.
> + * @genpd: Power domain to check.
> + */
> +static bool pm_genpd_powered_down(struct generic_power_domain *genpd)
> +{
> + bool ret;
> +
> + mutex_lock(&genpd->lock);
> + ret = genpd->power_is_off;
> + mutex_unlock(&genpd->lock);
> +
> + return ret;
> +}

What is the purpose of the mutex? On the face of it, there's nothing
to prevent another thread from changing the domain's power state in
between the mutex_unlock() call and the return statement.

Alan Stern



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