linux-kernel - Re: [PATCH 1/1] PM / Runtime: let rpm_resume fail if rpm disabled and device suspended.

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Date:	Mon, 16 Jun 2014 13:40:05 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Allen Yu <alleny@...dia.com>
cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] PM / Runtime: let rpm_resume fail if rpm disabled
 and device suspended.

On Sat, 14 Jun 2014, Allen Yu wrote:

> --- a/drivers/base/power/runtime.c
> +++ b/drivers/base/power/runtime.c
> @@ -608,7 +608,7 @@ static int rpm_resume(struct device *dev, int rpmflags)
>   repeat:
>  	if (dev->power.runtime_error)
>  		retval = -EINVAL;
> -	else if (dev->power.disable_depth == 1 && dev->power.is_suspended
> +	else if (dev->power.disable_depth == 1 && !dev->power.is_suspended
>  	    && dev->power.runtime_status == RPM_ACTIVE)
>  		retval = 1;

For reasons having nothing to do with Allen's suggested change, I
wonder if we shouldn't replace this line with something like:

-	else if (dev->power.disable_depth == 1 && dev->power.is_suspended
+	else if (dev->power.disable > 0 && !dev->power.is_suspended
	    && dev->power.runtime_status == RPM_ACTIVE)
		retval = 1;

It seems that I've been bitten by this several times in the past.  
When a device is disabled for runtime PM, and more or less permanently
stuck in the RPM_ACTIVE state, calls to pm_runtime_resume() or
pm_runtime_get_sync() shouldn't fail.

For example, suppose some devices of a certain type support runtime 
power management but others don't.  We naturally want to call 
pm_runtime_disable() for the ones that don't.  But we also want the 
same driver to work for all the devices, which means that 
pm_runtime_get_sync() should return success -- otherwise the driver 
will think that something has gone wrong.

Rafael, what do you think?

Alan Stern

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