linux-kernel - Re: Automatic clock disabling on clk

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Date:	Wed, 13 May 2015 08:45:50 +0200
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	Sascha Hauer <s.hauer@...gutronix.de>,
	Mike Turquette <mturquette@...aro.org>, kernel@...gutronix.de,
	linux-clk@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: Automatic clock disabling on clk_put()

Hello,

On Tue, May 12, 2015 at 04:23:48PM -0700, Stephen Boyd wrote:
> On 05/10/15 23:01, Sascha Hauer wrote:
> > Hi,
> >
> > Since we now have per-user clks we could automatically disable clks on
> > clk_put() to make the drivers errors paths easier. AFAIR that was one
> > of the motivations to switch to per user clks. Is this just not yet
> > implemented or are there problems implementing this?
> 
> I don't recall that as being a motivation for per-user clks. The
> documentation explicitly states:
> 
>  * Note: drivers must ensure that all clk_enable calls made on this
>  * clock source are balanced by clk_disable calls prior to calling
>  * this function.
> 
> so it seems that such a behavior would be an API change. Is it really
well, it's a compatible API change. So if you continue to use it as you
were obliged to do before, everything is fine. IMHO the introduction of
per-user clocks are a much bigger issue.

I'm not sure that auto disabling is a good idea[1], but at least giving a
warning should be possible.

> that hard to call clk_disable_unprepare() on a clock at the end of an
> error path? Maybe you could add a devm_clk_get_prepare_enable() that
> does what you want and then call clk_disable_unprepare on the exit path?
You mean clk_disable_unprepare is called in the same function that calls
clk_put I assume such that you don't have to do anything in the exit
path.

Best regards
Uwe

[1] mainly because I didn't think about it
-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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