linux-kernel - Re: [PATCH] usb: dwc3: keystone: switch to use runtime pm

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Message-ID: <20140131221118.GE2502@saruman.home>
Date:	Fri, 31 Jan 2014 16:11:19 -0600
From:	Felipe Balbi <balbi@...com>
To:	Alan Stern <stern@...land.harvard.edu>
CC:	Felipe Balbi <balbi@...com>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Grygorii Strashko <grygorii.strashko@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<ivan.khoronzhuk@...com>, <linux-usb@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: dwc3: keystone: switch to use runtime pm

On Fri, Jan 31, 2014 at 04:13:19PM -0500, Alan Stern wrote:
> On Fri, 31 Jan 2014, Felipe Balbi wrote:
> 
> > probe()
> > {
> > 	...
> > 
> > 	clk_get(dev, "fck");
> > 	clk_prepare(clk);
> > 	clk_enable(clk);
> > 	pm_runtime_set_active(dev);
> > 	pm_runtime_enable(dev);
> > 	pm_runtime_get_sync(dev);
> > 	...
> > }
> 
> > note that because of pm_runtime_set_active() that first
> > pm_runtime_get_sync() in probe() will simply increase the reference
> > counter without calling my ->runtime_resume() callback, which is exactly
> > what we want, as that would completely avoid situations of bad context
> > being restored because of that initial pm_runtime_get_sync().
> 
> Very minor note...  A slightly better way to do the same thing is:
> 
> 	pm_runtime_set_active(dev);
> 	pm_runtime_get_noresume(dev);
> 	pm_runtime_enable(dev);
> 
> The get_noresume says that you want to increment the usage counter
> without performing any callbacks, and doing it before the
> pm_runtime_enable avoids any window during which a runtime suspend
> might somehow occur.

aha, that's perfect :-) Thanks Alan.

-- 
balbi

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