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

Hi Uwe,

Thanks for the feedback, I'm not sure I like the more complex approach though:

Right, but I thought it a bit further than you did.  Like the following:

int clk_prepare(struct clk *clk)
{
	int ret = 0, first;
	unsigned long flags;

	spin_lock_irqsave(&clk->enable_lock, flags);
	if (clk->flags & CLK_BUSY) {
		/*
		 * this must not happen, please serialize calls to
		 * clk_prepare/clk_enable
		 */
		ret = -EBUSY;
		goto out_unlock;

Why is this an error? Two separate drivers may be clk_prepare()-ing at the 
same time, which should be acceptable. Both calls should block until the 
prepare is complete.

	}
	first = clk->prepare_count++ == 0;
	if (first)
		clk->flags |= CLK_BUSY;
	spin_unlock_irqrestore(&clk->enable_lock, flags);

	if (!first)
		return 0;

	if (clk->ops->prepare) {
		might_sleep();
		ret = clk->ops->prepare(clk);
	}

	spin_lock_irqsave(&clk->enable_lock, flags);
	clk->flags &= ~CLK_BUSY;
	if (ret)
		clk->prepare_count--;
out_unlock:
	spin_unlock_irqrestore(&clk->enable_lock, flags);

	return ret;
}

Cheers,


Jeremy