linux-kernel - Re: [PATCH] clk: bcm/kona: implement determine

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Message-ID: <20140523231849.23136.70991@quantum>
Date:	Fri, 23 May 2014 16:18:49 -0700
From:	Mike Turquette <mturquette@...aro.org>
To:	Alex Elder <elder@...aro.org>, mporter@...aro.org,
	bcm@...thebug.org
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clk: bcm/kona: implement determine_rate()

Quoting Alex Elder (2014-05-20 06:24:57)
> Implement the clk->determine_rate method for Broadcom Kona peripheral
> clocks.  This allows a peripheral clock to be re-parented in order to
> satisfy a rate change request.  This takes the place of the previous
> kona_peri_clk_round_rate() functionality, though that function remains
> because it is used by the new one.
> 
> The parent clock that allows the peripheral clock to produce a rate
> closest to the one requested is the one selected, though the current
> parent is used by default.
> 
> Signed-off-by: Alex Elder <elder@...aro.org>
> ---
> This patch is based on Mike Turquette's current "clk-next" branch.
>     6ed8eb5 Merge tag 'clk-hisi-for-v3.16' of https://git.kern...
> 
> It is available here:
>     http://git.linaro.org/landing-teams/working/broadcom/kernel.git
>     Branch review/bcm-determine-rate
> 
>  drivers/clk/bcm/clk-kona.c | 53 +++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 52 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/clk/bcm/clk-kona.c b/drivers/clk/bcm/clk-kona.c
> index d603c4e..1a4eccc 100644
> --- a/drivers/clk/bcm/clk-kona.c
> +++ b/drivers/clk/bcm/clk-kona.c
> @@ -1031,6 +1031,57 @@ static long kona_peri_clk_round_rate(struct clk_hw *hw, unsigned long rate,
>                                 rate ? rate : 1, *parent_rate, NULL);
>  }
>  
> +static long kona_peri_clk_determine_rate(struct clk_hw *hw, unsigned long rate,
> +               unsigned long *best_parent_rate, struct clk **best_parent)
> +{
> +       struct kona_clk *bcm_clk = to_kona_clk(hw);
> +       struct clk *clk = hw->clk;
> +       struct clk *current_parent;
> +       unsigned long parent_rate;
> +       unsigned long best_delta;
> +       unsigned long best_rate;
> +       u32 parent_count;
> +       u32 which;
> +
> +       /*
> +        * If there is no other parent to choose, use the current one.
> +        * Note:  We don't honor (or use) CLK_SET_RATE_NO_REPARENT.
> +        */

A WARN_ONCE is appropriate upon detection of CLK_SET_RATE_NO_REPARENT.
It will certainly help someone that is debugging why that flag has no
effect.

Otherwise the patch looks good to me.

Regards,
Mike

> +       parent_count = (u32)bcm_clk->init_data.num_parents;
> +       if (parent_count < 2)
> +               return kona_peri_clk_round_rate(hw, rate, best_parent_rate);
> +
> +       /* Unless we can do better, stick with current parent */
> +       current_parent = clk_get_parent(clk);
> +       parent_rate = __clk_get_rate(current_parent);
> +       best_rate = kona_peri_clk_round_rate(hw, rate, &parent_rate);
> +       best_delta = abs(best_rate - rate);
> +
> +       /* Check whether any other parent clock can produce a better result */
> +       for (which = 0; which < parent_count; which++) {
> +               struct clk *parent = clk_get_parent_by_index(clk, which);
> +               unsigned long delta;
> +               unsigned long other_rate;
> +
> +               BUG_ON(!parent);
> +               if (parent == current_parent)
> +                       continue;
> +
> +               /* We don't support CLK_SET_RATE_PARENT */
> +               parent_rate = __clk_get_rate(parent);
> +               other_rate = kona_peri_clk_round_rate(hw, rate, &parent_rate);
> +               delta = abs(other_rate - rate);
> +               if (delta < best_delta) {
> +                       best_delta = delta;
> +                       best_rate = other_rate;
> +                       *best_parent = parent;
> +                       *best_parent_rate = parent_rate;
> +               }
> +       }
> +
> +       return best_rate;
> +}
> +
>  static int kona_peri_clk_set_parent(struct clk_hw *hw, u8 index)
>  {
>         struct kona_clk *bcm_clk = to_kona_clk(hw);
> @@ -1135,7 +1186,7 @@ struct clk_ops kona_peri_clk_ops = {
>         .disable = kona_peri_clk_disable,
>         .is_enabled = kona_peri_clk_is_enabled,
>         .recalc_rate = kona_peri_clk_recalc_rate,
> -       .round_rate = kona_peri_clk_round_rate,
> +       .determine_rate = kona_peri_clk_determine_rate,
>         .set_parent = kona_peri_clk_set_parent,
>         .get_parent = kona_peri_clk_get_parent,
>         .set_rate = kona_peri_clk_set_rate,
> -- 
> 1.9.1
> 
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