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

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Date:	Fri, 4 Feb 2011 20:04:03 +0900
From:	Jassi Brar <jassisinghbrar@...il.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Richard Zhao <linuxzsc@...il.com>,
	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>,
	Stephen Boyd <sboyd@...eaurora.org>,
	linux-kernel@...r.kernel.org, Dima Zavin <dmitriyz@...gle.com>,
	Saravana Kannan <skannan@...eaurora.org>,
	Ben Dooks <ben-linux@...ff.org>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	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 Fri, Feb 4, 2011 at 7:48 PM, Russell King - ARM Linux
<linux@....linux.org.uk> wrote:

> int clk_enable(struct clk *clk)
> {
>        unsigned long flags;
>        int ret = 0;
>
>        if (clk) {
>                if (WARN_ON(!clk->prepare_count))
>                        return -EINVAL;
>
>                spin_lock_irqsave(&clk->lock, flags);
>                if (clk->enable_count++ == 0)
>                        ret = clk->ops->enable(clk);
>                spin_unlock_irqrestore(&clk->lock, flags);
>        }
>        return ret;
> }
>
> is entirely sufficient to catch the case of a single-use clock not being
> prepared before clk_enable() is called.
>
> We're after detecting drivers missing calls to clk_prepare(), we're not
> after detecting concurrent calls to clk_prepare()/clk_unprepare().

I hope you mean 'making sure the clock is prepared before it's enabled
' rather than
'catching a driver that doesn't do clk_prepare before clk_enable'.
Because, the above implementation still doesn't catch a driver that
doesn't call clk_prepare
but simply uses a clock that happens to have been already prepare'd by
some other
driver or the platform.
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