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

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Message-ID: <CACRpkdaeBW2ecQZ2fA-hL8o47pYpjZ=5Mn131F87u58rX+dekw@mail.gmail.com>
Date:	Wed, 24 Oct 2012 19:32:37 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Lee Jones <lee.jones@...aro.org>,
	Ulf Hansson <ulf.hansson@...aro.org>
Cc:	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, 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.

Yours,
Linus Walleij
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