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

["Jernej Škrabec" <jernej.skrabec@gmail.com>]

Dne sreda, 20. december 2023 ob 07:58:07 CET je Frank Oltmanns napisal(a):
> Hi Jernej!
> 
> On 2023-12-19 at 17:46:08 +0100, Jernej Škrabec <jernej.skrabec@gmail.com> wrote:
> > Hi Frank!
> >
> > Dne ponedeljek, 18. december 2023 ob 14:35:19 CET je Frank Oltmanns napisal(a):
> >> The Allwinner A64 manual lists the following constraints for the
> >> PLL-MIPI clock:
> >>  - M/N >= 3
> >
> > This should be "<="
> 
> Yes, good catch! I will fix it in V2.
> 
> >
> >>  - (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;
> >> +
> >
> > You already figured this part.
> >
> >>  				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;
> >
> > What about max_m_n_ratio and max_parent_m_ratio, to be consistent? This
> > should also allow to simplify description.
> 
> Jernej, thank you so much! This is brilliant! I was racking my brain for
> a good name but failed. Now, that I see your proposal, I don't know why
> I hadn't come up with it. It's the obvious choice.
> 
> I'd say with the new names we should be able to get rid of the comments
> describing the new struct members (also in ccu_nm.h). What are your
> thoughts on that?

Ah, I missed that only new ones are documented. Yeah, you can skip it.

Best regards,
Jernej

> 
> Best regards,
>   Frank
> 
> >
> > Best regards,
> > Jernej
> >
> >>
> >>  	struct ccu_common	common;
> >>  };
> >>
> >>
>