linux-kernel - Re: [RFC, PATCH 3/3] clk: add warnings for incorrect enable/prepare semantics

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Message-ID: <20110207080555.GC27982@pengutronix.de>
Date:	Mon, 7 Feb 2011 09:05:55 +0100
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Jeremy Kerr <jeremy.kerr@...onical.com>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	linux-sh@...r.kernel.org,
	Ben Herrenschmidt <benh@...nel.crashing.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Paul Mundt <lethal@...ux-sh.org>,
	Dima Zavin <dmitriyz@...gle.com>,
	Saravana Kannan <skannan@...eaurora.org>,
	Ben Dooks <ben-linux@...ff.org>,
	Russell King <linux@....linux.org.uk>
Subject: Re: [RFC, PATCH 3/3] clk: add warnings for incorrect
 enable/prepare semantics

Hello Jeremy,

On Mon, Feb 07, 2011 at 02:07:57PM +0800, Jeremy Kerr wrote:
> This change adds warnings to check for:
> 
>  1) enabling a clock that hasn't been prepared; and
> 
>  2) unpreparing a clock that is still enabled
> 
> While the correctness can't be guaranteed, these warnings should cover
> most situations.
> 
> Signed-off-by: Jeremy Kerr <jeremy.kerr@...onical.com>
> 
> ---
>  drivers/clk/clk.c |    4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index 51dbd33..2369959 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -35,6 +35,8 @@ void clk_unprepare(struct clk *clk)
>  	if (!clk->ops->unprepare)
>  		return;
>  
> +	WARN_ON(clk->enable_count);
> +
>  	mutex_lock(&clk->prepare_lock);
>  	if (--clk->prepare_count == 0)
>  		clk->ops->unprepare(clk);
> @@ -50,6 +52,8 @@ int clk_enable(struct clk *clk)
>  	if (!clk->ops->enable)
>  		return 0;
>  
> +	WARN_ON(clk->ops->prepare && clk->prepare_count);
> +
This implies the warning is only issued on clocks that have a prepare
callback.  If we want to enforce the new API the warning here shouldn't
depend on clk->ops->prepare.  (clk_prepare and clk_unprepare need to
be changed then to adapt the prepare_count even in the absence of
clk->ops->prepare.)

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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