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

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Message-ID: <537FD8AF.8060004@linaro.org>
Date:	Fri, 23 May 2014 18:24:31 -0500
From:	Alex Elder <elder@...aro.org>
To:	Mike Turquette <mturquette@...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()

On 05/23/2014 06:18 PM, Mike Turquette wrote:
> 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.

I'll add that.

> Otherwise the patch looks good to me.

Would you like me to send an updated patch as a pull request?

Thanks.

					-Alex

> 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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