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From:   Jernej =?utf-8?B?xaBrcmFiZWM=?= <jernej.skrabec@gmail.com>
To:     Maxime Ripard <mripard@kernel.org>,
        Michael Turquette <mturquette@baylibre.com>,
        Stephen Boyd <sboyd@kernel.org>, Chen-Yu Tsai <wens@csie.org>,
        Samuel Holland <samuel@sholland.org>,
        Andre Przywara <andre.przywara@arm.com>,
        Roman Beranek <me@crly.cz>, Frank Oltmanns <frank@oltmanns.dev>
Cc:     linux-clk@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-sunxi@lists.linux.dev, linux-kernel@vger.kernel.org,
        Frank Oltmanns <frank@oltmanns.dev>
Subject: Re: [PATCH v5 02/11] clk: sunxi-ng: nkm: consider alternative parent rates
 when determining rate
Date:   Sun, 06 Aug 2023 15:32:29 +0200
Message-ID: <3752134.kQq0lBPeGt@jernej-laptop>
In-Reply-To: <20230806-pll-mipi_set_rate_parent-v5-2-db4f5ca33fc3@oltmanns.dev>
References: <20230806-pll-mipi_set_rate_parent-v5-0-db4f5ca33fc3@oltmanns.dev>
 <20230806-pll-mipi_set_rate_parent-v5-2-db4f5ca33fc3@oltmanns.dev>
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Precedence: bulk

Dne nedelja, 06. avgust 2023 ob 15:06:47 CEST je Frank Oltmanns napisal(a):
> In case the CLK_SET_RATE_PARENT flag is set, consider using a different
> parent rate when determining a new rate.
> 
> To find the best match for the requested rate, perform the following
> steps for each NKM combination:
>  - calculate the optimal parent rate,
>  - find the best parent rate that the parent clock actually supports
>  - use that parent rate to calculate the effective rate.
> 
> In case the clk does not support setting the parent rate, use the same
> algorithm as before.
> 
> Acked-by: Maxime Ripard <mripard@kernel.org>
> Signed-off-by: Frank Oltmanns <frank@oltmanns.dev>
> ---
>  drivers/clk/sunxi-ng/ccu_nkm.c | 45
> +++++++++++++++++++++++++++++++++++++++++- 1 file changed, 44
> insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/clk/sunxi-ng/ccu_nkm.c b/drivers/clk/sunxi-ng/ccu_nkm.c
> index f267142e58b3..ea1b77e9b57f 100644
> --- a/drivers/clk/sunxi-ng/ccu_nkm.c
> +++ b/drivers/clk/sunxi-ng/ccu_nkm.c
> @@ -6,6 +6,7 @@
> 
>  #include <linux/clk-provider.h>
>  #include <linux/io.h>
> +#include <linux/math.h>

Why do you need above include?

Best regards,
Jernej

> 
>  #include "ccu_gate.h"
>  #include "ccu_nkm.h"
> @@ -16,6 +17,45 @@ struct _ccu_nkm {
>  	unsigned long	m, min_m, max_m;
>  };
> 
> +static unsigned long ccu_nkm_find_best_with_parent_adj(struct clk_hw
> *parent_hw, +						
       unsigned long *parent, unsigned long rate,
> +						       
struct _ccu_nkm *nkm)
> +{
> +	unsigned long best_rate = 0, best_parent_rate = *parent, tmp_parent 
=
> *parent; +	unsigned long best_n = 0, best_k = 0, best_m = 0;
> +	unsigned long _n, _k, _m;
> +
> +	for (_k = nkm->min_k; _k <= nkm->max_k; _k++) {
> +		for (_n = nkm->min_n; _n <= nkm->max_n; _n++) {
> +			for (_m = nkm->min_m; _m <= nkm->max_m; _m++) 
{
> +				unsigned long tmp_rate;
> +
> +				tmp_parent = 
clk_hw_round_rate(parent_hw, rate * _m / (_n * _k));
> +
> +				tmp_rate = tmp_parent * _n * _k / 
_m;
> +				if (tmp_rate > rate)
> +					continue;
> +
> +				if ((rate - tmp_rate) < (rate - 
best_rate)) {
> +					best_rate = tmp_rate;
> +					best_parent_rate = 
tmp_parent;
> +					best_n = _n;
> +					best_k = _k;
> +					best_m = _m;
> +				}
> +			}
> +		}
> +	}
> +
> +	nkm->n = best_n;
> +	nkm->k = best_k;
> +	nkm->m = best_m;
> +
> +	*parent = best_parent_rate;
> +
> +	return best_rate;
> +}
> +
>  static unsigned long ccu_nkm_find_best(unsigned long parent, unsigned long
> rate, struct _ccu_nkm *nkm)
>  {
> @@ -124,7 +164,10 @@ static unsigned long ccu_nkm_round_rate(struct
> ccu_mux_internal *mux, if (nkm->common.features &
> CCU_FEATURE_FIXED_POSTDIV)
>  		rate *= nkm->fixed_post_div;
> 
> -	rate = ccu_nkm_find_best(*parent_rate, rate, &_nkm);
> +	if (!clk_hw_can_set_rate_parent(&nkm->common.hw))
> +		rate = ccu_nkm_find_best(*parent_rate, rate, &_nkm);
> +	else
> +		rate = ccu_nkm_find_best_with_parent_adj(parent_hw, 
parent_rate, rate,
> &_nkm);
> 
>  	if (nkm->common.features & CCU_FEATURE_FIXED_POSTDIV)
>  		rate /= nkm->fixed_post_div;