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

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Message-ID: <20121025073127.GB971@gmail.com>
Date:	Thu, 25 Oct 2012 08:31:27 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	Ulf Hansson <ulf.hansson@...aro.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	arnd@...db.de, linus.walleij@...ricsson.com
Subject: Re: [PATCH 2/6] pinctrl: Update clock handling for the
 pinctrl-nomadik GPIO driver

On Wed, 24 Oct 2012, Linus Walleij wrote:

> On Wed, Oct 24, 2012 at 4:45 PM, Lee Jones <lee.jones@...aro.org> wrote:
> 
> > The clock framework has changed somewhat and it's now better to
> > invoke clock_prepare_enable() and clk_disable_unprepare() rather
> > than the legacy clk_enable() and clk_disable() calls. This patch
> > converts the Nomadik Pin Control driver to the new framework.
> >
> > Signed-off-by: Lee Jones <lee.jones@...aro.org>
> 
> (...)
> > -               clk_enable(chip->clk);
> > +               clk_prepare_enable(chip->clk);
> (...)
> > -               clk_disable(chip->clk);
> > +               clk_disable_unprepare(chip->clk);
> 
> (Repeated for each occurence.)
> 
> Is this *really* causing a regression? I mean the driver
> begin like this in nmk_gpio_probe():
> 
>         clk = devm_clk_get(&dev->dev, NULL);
>         if (IS_ERR(clk)) {
>                 ret = PTR_ERR(clk);
>                 goto out;
>         }
>         clk_prepare(clk);
> 
> Then it leaves the clock prepared. So the clock is always
> prepared. You would only need to enable/disable it at times.
> 
> And the semantics of the clk_enable/clk_disable call pair
> is such that it is fastpath and should be real quick, and that
> is exactly why we're using it repeatedly like that. Inserting
> clk_unprepare() effectively could make the whole driver a
> lot slower, so convince me on this one. ...
> 
> I suspect the real bug (if there is one) must be in the clock
> implementation.

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?

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