linux-kernel - Re: [PATCH] clk: add more managed APIs

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Date:   Sat, 28 Jan 2017 23:39:11 +0000
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clk: add more managed APIs

On Sat, Jan 28, 2017 at 01:44:35PM -0800, Guenter Roeck wrote:
> On 01/28/2017 11:22 AM, Dmitry Torokhov wrote:
> >Guenter, I know you are a coccinelle wizard, can you cook a script that
> >can find current users of clk_enable() in probe paths? Then we can make
> >informed decision on devm_clk_enable.
> >
> 
> Questionable use:
> 	drivers/input/keyboard/st-keyscan.c

clk_enable() without preceding clk_prepare() - buggy.

> 
> clk_enable() in probe, clk_disable() in remove:
> 	drivers/i2c/busses/i2c-tegra.c

Could be converted to use clk_prepare_enable() or clk_prepare()
depending on i2c_dev->is_multimaster_mode in the initialisation
path (and their devm_* equivalents.)

> 	drivers/media/platform/exynos4-is/fimc-core.c
> 	drivers/media/platform/exynos4-is/mipi-csis.c

Looks like it does a sequence of:

	devm_clk_get()
	clk_prepare()
	clk_set_rate()
	clk_enable()

which seems a little wrong - clk_set_rate() should be before
clk_prepare() if you care about not having the clock output.  Remember
that clk_prepare() _may_ result in the clock output being enabled.  So
these two look buggy, and when fixed could use devm_clk_prepare_enable().

> 	drivers/thermal/spear_thermal.c

clk_enable() without a preceding clk_prepare().  Buggy driver.

> 	drivers/usb/musb/am35x.c

Ditto.

> 	drivers/usb/musb/davinci.c

Ditto.

> Not that many. A quick browse suggests that clk_enable()/clk_disable()
> is more commonly used to temporarily enable the clock while needed.

So out of all those, there's probably only _one_ which is legit - the
rest are all technically buggy.

Given that, I'd say there's real reason _not_ to provide devm_clk_enable()
to persuade people to use the correct interfaces in the probe path.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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