linux-kernel - Re: [PATCH v3 01/11] usb: phy: Add APIs for runtime power management

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Date:	Wed, 3 Apr 2013 14:14:02 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Felipe Balbi <balbi@...com>
cc:	Vivek Gautam <gautamvivek1987@...il.com>,
	Kishon Vijay Abraham I <kishon@...com>,
	Vivek Gautam <gautam.vivek@...sung.com>,
	<linux-usb@...r.kernel.org>, <linux-samsung-soc@...r.kernel.org>,
	<linux-omap@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<gregkh@...uxfoundation.org>, <sarah.a.sharp@...ux.intel.com>,
	<rob.herring@...xeda.com>, <kgene.kim@...sung.com>,
	<dianders@...omium.org>, <t.figa@...sung.com>,
	<p.paneri@...sung.com>
Subject: Re: [PATCH v3 01/11] usb: phy: Add APIs for runtime power management

On Wed, 3 Apr 2013, Felipe Balbi wrote:

> > Lets suppose DWC3 enables runtime_pm on USB 2 type phy,
> > it will try to go into suspend state and thereby call runtime_suspend(), if any.
> > And PHY will come to active state only when its consumer wakes it up,
> > and this consumer is operational
> > only when its related PHY is in fully functional state.
> > So do we have a situation in which this PHY goes into low power state
> > in its runtime_suspend(),
> > resulting in non-detection of devices on further attach (since PHY is
> > in low power state) ?
> > 
> > Will the controller (like EHCI/OHCI) be functional now ?
> 
> ehci/ohci need to cope with that by calling usb_phy_autopm_get_sync(),
> right ? (so does DWC3 :-)

Maybe you guys have already got this all figured out -- if so, feel 
free to ignore this email.

Some subsystems handle this issue by calling pm_runtime_get_sync() 
before probing a driver and pm_runtime_put_sync() after unbinding the 
driver.  If the driver is runtime-PM-enabled, it then does its own 
put_sync near the end of its probe routine and get_sync in its release 
routine.

With PHYs you don't have probing and releasing, but you do have 
consumers registering and unregistering themselves, which is about the 
same thing.

Alan Stern

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