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

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Message-ID: <20110201140024.GZ1147@pengutronix.de>
Date:	Tue, 1 Feb 2011 15:00:24 +0100
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Jassi Brar <jassisinghbrar@...il.com>
Cc:	Jeremy Kerr <jeremy.kerr@...onical.com>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Russell King <linux@....linux.org.uk>,
	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>,
	Saravana Kannan <skannan@...eaurora.org>,
	Ben Dooks <ben-linux@...ff.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: Locking in the clk API, part 2: clk_prepare/clk_unprepare

On Tue, Feb 01, 2011 at 10:05:56PM +0900, Jassi Brar wrote:
> 2011/2/1 Uwe Kleine-König <u.kleine-koenig@...gutronix.de>:
> 
> .....
> 
> > Do you plan to handle the case that clk_enable is called while prepare
> > isn't completed (considering the special case "not called at all")?
> > Maybe BUG_ON(clk->ops->prepare && !clk->prepare_count)?
> Sounds better than the second option.
> 
> > Alternatively don't force the sleep in clk_prepare (e.g. by protecting
> > prepare_count by a spinlock (probably enable_lock)) and call clk_prepare
> > before calling clk->ops->enable?
> That might result in a driver working on some platforms(those have
> atomic clk_prepare)
> and not on others(those have sleeping).
The first option has the same result.  E.g. on some platforms
clk->ops->prepare might be NULL, on others it's not.

Uwe

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