linux-kernel - Re: Locking in the clk API, part 2: clk_prepare/clk

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Date:	Tue, 01 Feb 2011 12:59:11 -0800
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Saravana Kannan <skannan@...eaurora.org>,
	linux-sh@...r.kernel.org,
	Ben Herrenschmidt <benh@...nel.crashing.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Paul Mundt <lethal@...ux-sh.org>, linux-kernel@...r.kernel.org,
	Dima Zavin <dmitriyz@...gle.com>,
	Ben Dooks <ben-linux@...ff.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Jeremy Kerr <jeremy.kerr@...onical.com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: Locking in the clk API, part 2: clk_prepare/clk_unprepare

On 02/01/2011 07:24 AM, Russell King - ARM Linux wrote:
>
> I'd also be tempted at this stage to build-in a no-op dummy clock,
> that being the NULL clk:
>
> int clk_prepare(struct clk *clk)
> {
> 	int ret = 0;
>
> 	if (clk) {
> 		mutex_lock(&clk->mutex);
> 		if (clk->prepared == 0)
> 			ret = clk->ops->prepare(clk);
> 		if (ret == 0)
> 			clk->prepared++;
> 		mutex_unlock(&clk->mutex);
> 	}
>
> 	return ret;
> }

I'm afraid this will hide enable/disable imbalances on some targets and
then expose them on others. Maybe its not a big problem though since
this also elegantly handles the root(s) of the tree.

-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

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