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    SubjectRe: Locking in the clk API, part 2: clk_prepare/clk_unprepare
    From
    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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