Re: [PATCH v1] cpuidle: Do not return from cpuidle_play_dead() on callback failures

[Peter Zijlstra <peterz@infradead.org>]

On Thu, Nov 14, 2024 at 06:46:20PM +0100, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> If the :enter_dead() idle state callback fails for a certain state,
> there may be still a shallower state for which it will work.
> 
> Because the only caller of cpuidle_play_dead(), native_play_dead(),
> falls back to hlt_play_dead() if it returns an error, it should
> better try all of the idle states for which :enter_dead() is present
> before failing, so change it accordingly.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
>  drivers/cpuidle/cpuidle.c |    7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> Index: linux-pm/drivers/cpuidle/cpuidle.c
> ===================================================================
> --- linux-pm.orig/drivers/cpuidle/cpuidle.c
> +++ linux-pm/drivers/cpuidle/cpuidle.c
> @@ -70,9 +70,10 @@ int cpuidle_play_dead(void)
>  		return -ENODEV;
>  
>  	/* Find lowest-power state that supports long-term idle */
> -	for (i = drv->state_count - 1; i >= 0; i--)
> -		if (drv->states[i].enter_dead)
> -			return drv->states[i].enter_dead(dev, i);
> +	for (i = drv->state_count - 1; i >= 0; i--) {
> +		if (drv->states[i].enter_dead && !drv->states[i].enter_dead(dev, i))
> +			return 0;
> +	}

Hmm, strictly speaking there is no 'success' return from play_dead(). On
success, the CPU is dead :-)