From: Guenter Roeck <linux@roeck-us.net>
To: Russell King - ARM Linux <linux@armlinux.org.uk>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>,
Michael Turquette <mturquette@baylibre.com>,
Stephen Boyd <sboyd@codeaurora.org>,
Viresh Kumar <viresh.kumar@linaro.org>,
Andy Shevchenko <andy.shevchenko@gmail.com>,
linux-clk@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] clk: add more managed APIs
Date: Sun, 29 Jan 2017 08:00:20 -0800 [thread overview]
Message-ID: <71ad5742-6264-6864-69f9-288609617340@roeck-us.net> (raw)
In-Reply-To: <20170128233911.GO27312@n2100.armlinux.org.uk>
On 01/28/2017 03:39 PM, Russell King - ARM Linux wrote:
> 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.
>
I tend to agree, after looking into its existing use.
Do we have agreement on the other two ? I would like to see those in the
next release so we can start using them.
Thanks,
Guenter
next prev parent reply other threads:[~2017-01-29 16:00 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-28 18:40 [PATCH] clk: add more managed APIs Dmitry Torokhov
2017-01-28 19:03 ` Russell King - ARM Linux
2017-01-28 19:22 ` Dmitry Torokhov
2017-01-28 21:44 ` Guenter Roeck
2017-01-28 23:39 ` Russell King - ARM Linux
2017-01-29 16:00 ` Guenter Roeck [this message]
2017-01-29 18:07 ` [PATCH v2] " Dmitry Torokhov
2017-01-29 18:31 ` Guenter Roeck
2017-01-30 18:55 ` Stephen Boyd
2017-01-30 19:22 ` Guenter Roeck
2017-01-30 21:42 ` Russell King - ARM Linux
2017-01-30 21:58 ` Dmitry Torokhov
2017-01-30 22:25 ` Russell King - ARM Linux
2017-01-30 22:51 ` Guenter Roeck
2017-01-31 8:43 ` Geert Uytterhoeven
2017-01-31 0:59 ` Dmitry Torokhov
2017-01-31 17:20 ` Guenter Roeck
2017-01-31 18:26 ` Dmitry Torokhov
2017-01-31 19:34 ` Guenter Roeck
2017-01-31 0:57 ` [PATCH v3] " Dmitry Torokhov
2017-02-07 3:51 ` Dmitry Torokhov
2017-02-14 19:44 ` Stephen Boyd
2017-02-14 19:55 ` Dmitry Torokhov
2017-02-14 20:31 ` Guenter Roeck
2017-02-14 20:01 ` Russell King - ARM Linux
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