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

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Message-ID: <20110201170637.GR31216@n2100.arm.linux.org.uk>
Date:	Tue, 1 Feb 2011 17:06:37 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
Cc:	Jeremy Kerr <jeremy.kerr@...onical.com>,
	Dima Zavin <dmitriyz@...gle.com>,
	Saravana Kannan <skannan@...eaurora.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	linux-sh@...r.kernel.org,
	Ben Herrenschmidt <benh@...nel.crashing.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	linux-kernel@...r.kernel.org, Paul Mundt <lethal@...ux-sh.org>,
	Ben Dooks <ben-linux@...ff.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	linux-arm-kernel@...ts.infradead.org,
	Nicolas Pitre <nicolas.pitre@...aro.org>
Subject: Re: Locking in the clk API, part 2: clk_prepare/clk_unprepare

On Tue, Feb 01, 2011 at 04:53:44PM +0100, Uwe Kleine-König wrote:
> On Tue, Feb 01, 2011 at 03:24:58PM +0000, Russell King - ARM Linux wrote:
> > On Tue, Feb 01, 2011 at 04:18:46PM +0100, Uwe Kleine-König wrote:
> > > yeah, didn't thought about multiple consumers, so (as Jeremy suggested)
> > > the right thing is to sleep until CLK_BUSY is cleared.
> > 
> > A simpler way to write this is:
> > 
> > int clk_prepare(struct clk *clk)
> > {
> > 	int ret = 0;
> > 
> > 	mutex_lock(&clk->mutex);
> > 	if (clk->prepared == 0)
> > 		ret = clk->ops->prepare(clk);
> > 	if (ret == 0)
> > 		clk->prepared++;
> > 	mutex_unlock(&clk->mutex);
> > 
> > 	return ret;
> > }
> But you cannot call this in atomic context when you know the clock is
> already prepared.

So?  You're not _supposed_ to call it from any atomic context ever.
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