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

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Message-ID: <alpine.LFD.2.00.1102011503550.8580@xanadu.home>
Date:	Tue, 1 Feb 2011 15:06:09 -0500 (EST)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	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 Tue, 1 Feb 2011, Uwe Kleine-König wrote:

> My motivation for a more complicated clk_prepare was to make clk_prepare
> atomic when that's possible (i.e. when the clk is already prepared) and
> call it before the enable callback in clk_enable.  Then everything
> behaves nicely even if clk_enable is called from atomic context provided
> that the clock was prepared before (or doesn't need to).

NOOOOOOOOO!!!

We _do_ want drivers to _always_ call clk_prepare() in sleepable 
context, and _then_ always call clk_enable() in whatever context they 
wish.  Period.


Nicolas