Re: [PATCH 1/5] clk: sunxi-ng: nkm: Support constraints on m/n ratio and parent rate

[Frank Oltmanns <frank@oltmanns.dev>]

On 2023-12-18 at 14:35:19 +0100, Frank Oltmanns <frank@oltmanns.dev> wrote:
> The Allwinner A64 manual lists the following constraints for the
> PLL-MIPI clock:
>  - M/N >= 3
>  - (PLL_VIDEO0)/M >= 24MHz
>
> The PLL-MIPI clock is implemented as ccu_nkm. Therefore, add support for
> these constraints.
>
> Signed-off-by: Frank Oltmanns <frank@oltmanns.dev>
> ---
>  drivers/clk/sunxi-ng/ccu_nkm.c | 23 +++++++++++++++++++++++
>  drivers/clk/sunxi-ng/ccu_nkm.h |  8 ++++++++
>  2 files changed, 31 insertions(+)
>
> diff --git a/drivers/clk/sunxi-ng/ccu_nkm.c b/drivers/clk/sunxi-ng/ccu_nkm.c
> index eed64547ad42..2af5c1ebd527 100644
> --- a/drivers/clk/sunxi-ng/ccu_nkm.c
> +++ b/drivers/clk/sunxi-ng/ccu_nkm.c
> @@ -16,6 +16,20 @@ struct _ccu_nkm {
>  	unsigned long	m, min_m, max_m;
>  };
>
> +static bool ccu_nkm_is_valid_rate(struct ccu_common *common, unsigned long parent,
> +				  unsigned long n, unsigned long m)
> +{
> +	struct ccu_nkm *nkm = container_of(common, struct ccu_nkm, common);
> +
> +	if (nkm->max_mn_ratio && (m > nkm->max_mn_ratio * n))
> +		return false;
> +
> +	if (nkm->parent_wo_nk && (parent < nkm->parent_wo_nk * m))
> +		return false;
> +
> +	return true;
> +}
> +
>  static unsigned long ccu_nkm_find_best_with_parent_adj(struct ccu_common *common,
>  						       struct clk_hw *parent_hw,
>  						       unsigned long *parent, unsigned long rate,
> @@ -32,6 +46,9 @@ static unsigned long ccu_nkm_find_best_with_parent_adj(struct ccu_common *common
>
>  				tmp_parent = clk_hw_round_rate(parent_hw, rate * _m / (_n * _k));
>
> +				if (!ccu_nkm_is_valid_rate(common, tmp_parent, _n, _m))
> +					continue;
> +
>  				tmp_rate = tmp_parent * _n * _k / _m;
>
>  				if (ccu_is_better_rate(common, rate, tmp_rate, best_rate) ||
> @@ -65,6 +82,12 @@ static unsigned long ccu_nkm_find_best(unsigned long parent, unsigned long rate,
>  	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++) {
> +				if ((common->reg == 0x040) && (_m > 3 * _n))
> +					break;
> +
> +				if ((common->reg == 0x040) && (parent < 24000000 * _m))
> +					continue;
> +

This, of course, is rubbish and should be this instead:
+				if (!ccu_nkm_is_valid_rate(common, parent, _n, _m))
+					continue;
+

I'll submit a V2 after receiving some feedback.

>  				unsigned long tmp_rate;
>
>  				tmp_rate = parent * _n * _k / _m;
> diff --git a/drivers/clk/sunxi-ng/ccu_nkm.h b/drivers/clk/sunxi-ng/ccu_nkm.h
> index 6601defb3f38..d3d3eaf55faf 100644
> --- a/drivers/clk/sunxi-ng/ccu_nkm.h
> +++ b/drivers/clk/sunxi-ng/ccu_nkm.h
> @@ -16,6 +16,12 @@
>   * struct ccu_nkm - Definition of an N-K-M clock
>   *
>   * Clocks based on the formula parent * N * K / M
> + *
> + * @max_mn_ratio:	Maximum value for M / N.
> + * @parent_wo_nk:	The minimum rate the parent must provide after applying the divisor,
> + *			but without applying the multipliers, i.e. the contstraint
> + *			   (parent rate)/M >= parent_wo_nk
> + *			must be fulfilled.
>   */
>  struct ccu_nkm {
>  	u32			enable;
> @@ -27,6 +33,8 @@ struct ccu_nkm {
>  	struct ccu_mux_internal	mux;
>
>  	unsigned int		fixed_post_div;
> +	unsigned long		max_mn_ratio;
> +	unsigned long           parent_wo_nk;
>
>  	struct ccu_common	common;
>  };