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Date: Fri, 4 Feb 2011 20:04:03 +0900
Message-ID: <AANLkTi=sfBTHLXejWxAWGa=Tcw+LoQfw6sUtcn6L+JeM@mail.gmail.com>
Subject: Re: Locking in the clk API, part 2: clk_prepare/clk_unprepare
From: Jassi Brar <jassisinghbrar@gmail.com>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: Richard Zhao <linuxzsc@gmail.com>,
        Nicolas Pitre <nicolas.pitre@linaro.org>,
        Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com>,
        Vincent Guittot <vincent.guittot@linaro.org>, linux-sh@vger.kernel.org,
        Ben Herrenschmidt <benh@kernel.crashing.org>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        Paul Mundt <lethal@linux-sh.org>, Stephen Boyd <sboyd@codeaurora.org>,
        linux-kernel@vger.kernel.org, Dima Zavin <dmitriyz@google.com>,
        Saravana Kannan <skannan@codeaurora.org>,
        Ben Dooks <ben-linux@fluff.org>,
        =?UTF-8?Q?Uwe_Kleine=2DK=C3=B6nig?= 
	<u.kleine-koenig@pengutronix.de>,
        Jeremy Kerr <jeremy.kerr@canonical.com>,
        linux-arm-kernel@lists.infradead.org
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On Fri, Feb 4, 2011 at 7:48 PM, Russell King - ARM Linux
<linux@arm.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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