[PATCH 05/10] clk: Add support for simple dividers

[Sascha Hauer]

On Thu, Apr 28, 2011 at 04:22:17PM +0100, Russell King - ARM Linux wrote:
> On Mon, Apr 18, 2011 at 11:49:09AM +0200, Uwe Kleine-König wrote:
> > > +static int clk_divider_set_rate(struct clk *clk, unsigned long rate)
> > > +{
> > > +	unsigned long best_parent_rate;
> > > +	struct clk_divider *divider = to_clk_divider(clk);
> > > +	unsigned int div;
> > > +	int ret;
> > > +	unsigned long flags = 0;
> > > +	u32 val;
> > > +
> > > +	div = clk_divider_bestdiv(clk, rate, &best_parent_rate);
> > > +
> > > +	if (rate != best_parent_rate / div)
> > > +		return -EINVAL;
> > This is too harsh, isn't it. Or can you expect to only get values that
> > are returned by round_rate? Again you need DIV_ROUND_UP.
> 
> It is too harsh, and I've wished many a time that people would implement
> clk_set_rate() and clk_round_rate() as:
> 
> long clk_round_rate(struct clk *clk, unsigned long rate)
> {
> 	err = calculate_clock_paramters(clk, params, rate);
> 	if (err < 0)
> 		return err;
> 	return calculate_clock_rate(clk, params);
> }
> 
> int clk_set_rate(struct clk *clk, unsigned long rate)
> {
> 	err = calculate_clock_parameters(clk, params, rate);
> 	if (err < 0)
> 		return err;
> 	set_clock_parameters(clk, params);
> 	clk->rate = calculate_clock_rate(clk, params);
> 	return 0;
> }
> 
> IOW, clk_round_rate() does what clk_set_rate() does but does _not_ set
> the hardware rate itself.

Ok. It's easier to implement anyway since rounding errors do not have
such a bad impact.

Sascha


-- 
Pengutronix e.K.                           |                             |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |