On Thu, May 21, 2015 at 4:57 PM, Ezequiel Garcia
<ezequiel.garcia@xxxxxxxxxx> wrote:
> This commit implements small rate changes to the fractional PLL.
> This is done using the PLL frac parameter. The .set_rate function
> first finds the parameters associated to the closest nominal rate.
>
> Then the new rate is set, using parameters from the table entry,
> except for the frac parameter, which is calculated from the rate
> using the fractional PLL rate formula.
>
> Using .round_rate, the driver guarantees that only rates near
> a table nominal rate is applied. To this extent, add two parameters
> fout_min and fout_max, which allows to define the allowed rate
> adjustment.
>
> Signed-off-by: Ezequiel Garcia <ezequiel.garcia@xxxxxxxxxx>
> ---
> drivers/clk/pistachio/clk-pll.c | 48 +++++++++++++++++++++++++++++++----------
> drivers/clk/pistachio/clk.h | 2 ++
> 2 files changed, 39 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/clk/pistachio/clk-pll.c b/drivers/clk/pistachio/clk-pll.c
> index f12d520..cf000bb 100644
> --- a/drivers/clk/pistachio/clk-pll.c
> +++ b/drivers/clk/pistachio/clk-pll.c
> @@ -90,29 +90,50 @@ static struct pistachio_pll_rate_table *
> pll_get_params(struct pistachio_clk_pll *pll, unsigned long fref,
> unsigned long fout)
> {
> - unsigned int i;
> + unsigned int i, best;
> + unsigned long err, best_err = ~0;
>
> for (i = 0; i < pll->nr_rates; i++) {
> - if (pll->rates[i].fref == fref && pll->rates[i].fout == fout)
> - return &pll->rates[i];
> + err = abs(pll->rates[i].fout - fout);
> + if (pll->rates[i].fref == fref && err < best_err) {
> + best = i;
> + best_err = err;
> + }
> }
>
> - return NULL;
> + return &pll->rates[best];
> }
>
> static long pll_round_rate(struct clk_hw *hw, unsigned long rate,
> unsigned long *parent_rate)
> {
> struct pistachio_clk_pll *pll = to_pistachio_pll(hw);
> - unsigned int i;
> + unsigned int i, best;
> + unsigned long err, best_err = ~0;
>
> for (i = 0; i < pll->nr_rates; i++) {
> - if (i > 0 && pll->rates[i].fref == *parent_rate &&
> - pll->rates[i].fout <= rate)
> - return pll->rates[i - 1].fout;
> + err = abs(pll->rates[i].fout - rate);
> + if (pll->rates[i].fref == *parent_rate && err < best_err) {
> + best = i;
> + best_err = err;
> + }
> }
>
> - return pll->rates[0].fout;
> + /* Make sure fout_{min,max} parameters have sane values */
> + if (!pll->rates[best].fout_min)
> + pll->rates[best].fout_min = pll->rates[best].fout;
> + if (!pll->rates[best].fout_max)
> + pll->rates[best].fout_max = pll->rates[best].fout;
Perhaps the rate tables should just always populate fout_min and fout_max?
