linux-kernel - Re: [PATCH v2 2/5] cpu_pm: call notifiers during suspend

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Date:	Wed, 07 Sep 2011 13:02:59 -0700
From:	Kevin Hilman <khilman@...com>
To:	Santosh Shilimkar <santosh.shilimkar@...com>
Cc:	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <linux@....linux.org.uk>,
	<ccross@...roid.com>, <rjw@...k.pl>
Subject: Re: [PATCH v2 2/5] cpu_pm: call notifiers during suspend

Santosh Shilimkar <santosh.shilimkar@...com> writes:

> From: Colin Cross <ccross@...roid.com>
>
> Implements syscore_ops in cpu_pm to call the cpu and
> cpu cluster notifiers during suspend and resume,
> allowing drivers receiving the notifications to
> avoid implementing syscore_ops.
>
> Signed-off-by: Colin Cross <ccross@...roid.com>
> [santosh.shilimkar@...com: Rebased against 3.1-rc4]
> Signed-off-by: Santosh Shilimkar <santosh.shilimkar@...com>

I don't think using syscore_ops is right here.  The platform code should
decide where in its own suspend path the notifiers should be triggered.

The reason is because while the syscore_ops run late in the suspend
path, they still run before some platform-specific decisions about the
low-power states are made.  That means that any notifiers that need to
use information about the target low-power state (e.g. whether context
will be lost or not) cannot do so since that information has not yet
been decided until the platform_suspend_ops->enter() runs.

Basically, I think the cpu_*_pm_enter() calls should be called by
platform-specific code, not by common code.

Kevin

> ---
>  kernel/cpu_pm.c |   33 +++++++++++++++++++++++++++++++++
>  1 files changed, 33 insertions(+), 0 deletions(-)
>
> diff --git a/kernel/cpu_pm.c b/kernel/cpu_pm.c
> index 54aa892..3d115d0 100644
> --- a/kernel/cpu_pm.c
> +++ b/kernel/cpu_pm.c
> @@ -20,6 +20,7 @@
>  #include <linux/module.h>
>  #include <linux/notifier.h>
>  #include <linux/spinlock.h>
> +#include <linux/syscore_ops.h>
>  
>  static DEFINE_RWLOCK(cpu_pm_notifier_lock);
>  static RAW_NOTIFIER_HEAD(cpu_pm_notifier_chain);
> @@ -113,3 +114,35 @@ int cpu_cluster_pm_exit(void)
>  	return ret;
>  }
>  EXPORT_SYMBOL_GPL(cpu_cluster_pm_exit);
> +
> +#ifdef CONFIG_PM
> +static int cpu_pm_suspend(void)
> +{
> +	int ret;
> +
> +	ret = cpu_pm_enter();
> +	if (ret)
> +		return ret;
> +
> +	ret = cpu_cluster_pm_enter();
> +	return ret;
> +}
> +
> +static void cpu_pm_resume(void)
> +{
> +	cpu_cluster_pm_exit();
> +	cpu_pm_exit();
> +}
> +
> +static struct syscore_ops cpu_pm_syscore_ops = {
> +	.suspend = cpu_pm_suspend,
> +	.resume = cpu_pm_resume,
> +};
> +
> +static int cpu_pm_init(void)
> +{
> +	register_syscore_ops(&cpu_pm_syscore_ops);
> +	return 0;
> +}
> +core_initcall(cpu_pm_init);
> +#endif
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