linux-kernel - Re: [PATCH 2/6] pinctrl: Update clock handling for the pinctrl-nomadik GPIO driver

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Message-ID: <20121025094458.GB4008@gmail.com>
Date:	Thu, 25 Oct 2012 10:44:58 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	Ulf Hansson <ulf.hansson@...aro.org>
Cc:	Linus Walleij <linus.walleij@...ricsson.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"arnd@...db.de" <arnd@...db.de>
Subject: Re: [PATCH 2/6] pinctrl: Update clock handling for the
 pinctrl-nomadik GPIO driver

On Thu, 25 Oct 2012, Ulf Hansson wrote:

> On 25 October 2012 10:23, Lee Jones <lee.jones@...aro.org> wrote:
> > On Thu, 25 Oct 2012, Linus Walleij wrote:
> >
> >> On 10/25/2012 09:31 AM, Lee Jones wrote:
> >> >
> >> >This certainly doesn't fix the bug we spoke about. I believe Ulf
> >> >is still working on that one.
> >> >
> >> >So do you want me to remove this patch?
> >> >
> >>
> >> Yeah drop it for now.
> >
> > Actually, a quick question before I do:
> >
> > If it's better/faster to prepare the clock and keep it prepared
> > while you do clk_enable/clk_disable, why don't we do that in all
> > drivers? Why do we bother to prepare/unprepare each time if all
> > it does is take up cycles?
> >
> 
> Depending on clock type, a clk_disable is actually not going to "gate"
> the clock, that might happen only in unprepare. This depends on if the
> clock is a fast or slow clock.
> To save as much power as possible, in general, we should do both
> disable and unprepare. Although it will be device driver dependent
> were it is most convenient to do this things.
> Sometimes it is possible to group them sometimes not.

And in this case, it's better to ... ?

-- 
Lee Jones
Linaro ST-Ericsson Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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