linux-kernel - Re: [PATCH 3/9] clk: pistachio: Implement PLL rate adjustment

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Date:	Fri, 22 May 2015 10:04:34 -0700
From:	Andrew Bresticker <abrestic@...omium.org>
To:	Ezequiel Garcia <ezequiel.garcia@...tec.com>
Cc:	Linux-MIPS <linux-mips@...ux-mips.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Mike Turquette <mturquette@...aro.org>,
	Stephen Boyd <sboyd@...eaurora.org>,
	James Hartley <james.hartley@...tec.com>,
	Govindraj Raja <Govindraj.Raja@...tec.com>,
	Damien Horsley <Damien.Horsley@...tec.com>,
	Kevin Cernekee <cernekee@...omium.org>,
	James Hogan <james.hogan@...tec.com>
Subject: Re: [PATCH 3/9] clk: pistachio: Implement PLL rate adjustment

On Thu, May 21, 2015 at 4:57 PM, Ezequiel Garcia
<ezequiel.garcia@...tec.com> 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@...tec.com>
> ---
>  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?
--
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