Re: [PATCH E 10/14] OMAP clock: support "dry run" rate and parent changes

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

On Wed, Jan 28, 2009 at 12:27:56PM -0700, Paul Walmsley wrote:
> For upcoming notifier support, modify the rate recalculation code to
> take parent rate and rate storage parameters.  The goal here is to
> allow the clock code to determine what the clock's rate would be after
> a parent change or a rate change, without actually changing the
> hardware registers.  This is used by the upcoming notifier patches to
> pass a clock's current and planned rates to the notifier callbacks.

NAK.  I'm not sure whether you've realised, but this is exactly what the
'round_rate' method is supposed to be doing.  It provides a method by
which you can find out what the clock rate would be if you asked for
'set_rate' to set the hardware to the requested rate.

A far better way to approach this would be to split the set_rate/recalc
functionality into two parts:

1. a method which returns the both the new clock rate and the hardware
   programming information
2. a method to commit the hardware programming information to the registers

(1) can be used for implementing clk_round_rate() (which is totally lacking
in OMAP2+, yet is implemented in OMAP1), clk_set_rate(), clk_set_parent()
etc.

(2) can be used when it's required to actually reprogram the hardware.

So, rather than the current situation where we have recalc, round_rate
and set_rate methods, we have calc_rate() and commit() methods instead
and have the core clock code sort out calling these.

IOW, clk_set_rate() and clk_round_rate() becomes:

int clk_set_rate(struct clk *clk, unsigned long rate)
{
	unsigned long flags;
	int ret = -EINVAL;

        spin_lock_irqsave(&clockfw_lock, flags);
	if (clk->calc_rate) {
		unsigned long parent_rate = 0;
		struct clk_hw hw;

		if (clk->parent)
			parent_rate = clk->parent->rate;

		ret = clk->calc_rate(clk, parent_rate, &rate, &hw);
		if (ret == 0) {
			clk->rate = rate;
			clk->commit(clk, &hw);
		}
	}
        spin_unlock_irqrestore(&clockfw_lock, flags);

	return ret;
}

long clk_round_rate(struct clk *clk, unsigned long rate)
{
	unsigned long flags;
	long ret;

        spin_lock_irqsave(&clockfw_lock, flags);
	if (clk->calc_rate) {
		unsigned long parent_rate = 0;
		struct clk_hw hw;

		if (clk->parent)
			parent_rate = clk->parent->rate;

		ret = clk->calc_rate(clk, parent_rate, &rate, &hw);
		if (ret == 0)
			ret = rate;
	}
        spin_unlock_irqrestore(&clockfw_lock, flags);

	return ret;
}