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SubjectRe: Locking in the clk API, part 2: clk_prepare/clk_unprepare
On Tue, Feb 01, 2011 at 04:18:46PM +0100, Uwe Kleine-König wrote:
> yeah, didn't thought about multiple consumers, so (as Jeremy suggested)
> the right thing is to sleep until CLK_BUSY is cleared.

A simpler way to write this is:

int clk_prepare(struct clk *clk)
{
int ret = 0;

mutex_lock(&clk->mutex);
if (clk->prepared == 0)
ret = clk->ops->prepare(clk);
if (ret == 0)
clk->prepared++;
mutex_unlock(&clk->mutex);

return ret;
}

I think we want to take a common mutex not only for clk_prepare(), but
also for clk_set_rate(). If prepare() is waiting for a PLL to lock,
we don't want a set_rate() interfering with that.

I'd also be tempted at this stage to build-in a no-op dummy clock,
that being the NULL clk:

int clk_prepare(struct clk *clk)
{
int ret = 0;

if (clk) {
mutex_lock(&clk->mutex);
if (clk->prepared == 0)
ret = clk->ops->prepare(clk);
if (ret == 0)
clk->prepared++;
mutex_unlock(&clk->mutex);
}

return ret;
}

as we have various platforms defining a dummy struct clk as a way of
satisfying various driver requirements. These dummy clocks are exactly
that - they're complete no-ops.
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