linux-kernel - Re: [RFC PATCH 4/6] USB: ehci-omap: Suspend the controller during bus suspend

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Date:	Thu, 20 Jun 2013 15:32:01 +0300
From:	Roger Quadros <rogerq@...com>
To:	Kevin Hilman <khilman@...aro.org>
CC:	<stern@...land.harvard.edu>, <tony@...mide.com>, <balbi@...com>,
	<ruslan.bilovol@...com>, <linux-usb@...r.kernel.org>,
	<linux-omap@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC PATCH 4/6] USB: ehci-omap: Suspend the controller during
 bus suspend

On 06/19/2013 08:39 PM, Kevin Hilman wrote:
> Hi Roger,
> 
> Roger Quadros <rogerq@...com> writes:
> 
>> Runtime suspend the controller during bus suspend and resume it
>> during bus resume. This will ensure that the USB Host power domain
>> enters lower power state and does not prevent the SoC from
>> endering deeper sleep states.
>>
>> Remote wakeup will come up as an interrupt while the controller
>> is suspended, so tackle it carefully using a workqueue.
> 
> I don't think you need a special workqueue here.  The workqueue of the PM
> core (pm_wq) will be used if you just use an asynchronous 'get' in the
> ISR.  Then, the driver's own runtime PM callbacks can be used instead of
> an additional workqueue.
> 
> Another thing to worry about here when using runtime PM to implement
> suspend/resume is that runtime PM can be disabled from userspace (e.g.
> echo disabled > /sys/devices/.../power/control.)  If that's the case,
> all the pm_runtime_suspended() checks will always fail becuase that
> call also checks if runtime PM is disabled.  You'll likely want to use
> the pm_runtime_status_suspended() check instead, which checks only the
> status, and doesn't matter if runtime PM is currently disabled.
> 
> Because of the corner issues here, please test system suspend/resume
> when runtime PM has been disabled.
> 

Good points. Thanks. I'll need to think about it some more.

cheers,
-roger
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