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

Sascha Hauer
2011-05-02T07:58:56Z

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-K?nig 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

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