linux-kernel - Re: [PATCH v2 3/4] clk: spacemit: introduce factor for div clock

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Message-ID: <aKKN05w88uKP_HY7@ketchup>
Date: Mon, 18 Aug 2025 02:20:03 +0000
From: Haylen Chu <heylenay@....org>
To: Troy Mitchell <troy.mitchell@...ux.spacemit.com>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...nel.org>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, Yixun Lan <dlan@...too.org>,
	Alex Elder <elder@...cstar.com>,
	Inochi Amaoto <inochiama@...look.com>
Cc: linux-clk@...r.kernel.org, devicetree@...r.kernel.org,
	linux-riscv@...ts.infradead.org, spacemit@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	Jinmei Wei <weijinmei@...ux.spacemit.com>
Subject: Re: [PATCH v2 3/4] clk: spacemit: introduce factor for div clock

On Mon, Aug 11, 2025 at 10:04:29PM +0800, Troy Mitchell wrote:
> From the definition of register, The i2s_bclk is a non-linear,
> discrete divider clock.
> 
> The following table shows the correspondence between index
> and frequency division coefficients:
> 
> | index |  div  |
> |-------|-------|
> |   0   |   2   |
> |   1   |   4   |
> |   2   |   6   |
> |   3   |   8   |
> 
> But from a software perspective and this table, dividing the
> actual div value by 2 is sufficient to obtain a continuous
> divider clock.
> 
> Rather than introducing a new clock type to handle this case,
> a factor parameter has been added to CCU_DIV_GATE_DEFINE.

Actually, I expected you to represent the factor simply with
CCU_FACTOR_DEFINE, introducing no new clock-calculation code...

> Suggested-by: Haylen Chu <heylenay@....org>
> Signed-off-by: Troy Mitchell <troy.mitchell@...ux.spacemit.com>
> ---
>  drivers/clk/spacemit/ccu_mix.c | 7 ++++++-
>  drivers/clk/spacemit/ccu_mix.h | 4 +++-
>  2 files changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/clk/spacemit/ccu_mix.c b/drivers/clk/spacemit/ccu_mix.c
> index 9b852aa61f78aed5256bfe6fc3b01932d6db6256..dbd2cf234bf81d8e110b19868ff9af7373e2ab55 100644
> --- a/drivers/clk/spacemit/ccu_mix.c
> +++ b/drivers/clk/spacemit/ccu_mix.c
> @@ -56,7 +56,10 @@ static unsigned long ccu_div_recalc_rate(struct clk_hw *hw,
>  	val = ccu_read(&mix->common, ctrl) >> div->shift;
>  	val &= (1 << div->width) - 1;
>  
> -	return divider_recalc_rate(hw, parent_rate, val, NULL, 0, div->width);
> +	if (!div->factor)
> +		return divider_recalc_rate(hw, parent_rate, val, NULL, 0, div->width);

Please adapt all div-related macros to make them assign one to the
factor, which helps you get rid of this if and the one in
ccu_mix_calc_best_rate().

> +	return divider_recalc_rate(hw, parent_rate, val, NULL, 0, div->width) / div->factor;
>  }
>  
>  /*
> @@ -115,6 +118,8 @@ ccu_mix_calc_best_rate(struct clk_hw *hw, unsigned long rate,
>  
>  		for (int j = 1; j <= div_max; j++) {
>  			unsigned long tmp = DIV_ROUND_CLOSEST_ULL(parent_rate, j);
> +			if (mix->div.factor)
			---- this if ------

> +				tmp /= mix->div.factor;
>  
>  			if (abs(tmp - rate) < abs(best_rate - rate)) {
>  				best_rate = tmp;
> diff --git a/drivers/clk/spacemit/ccu_mix.h b/drivers/clk/spacemit/ccu_mix.h
> index 54d40cd39b2752260f57d2a96eb8d3eed8116ecd..7dd00d24ec4b1dab70663b9cb7b9ebb02abeaecb 100644
> --- a/drivers/clk/spacemit/ccu_mix.h
> +++ b/drivers/clk/spacemit/ccu_mix.h
> @@ -34,6 +34,7 @@ struct ccu_mux_config {
>  struct ccu_div_config {
>  	u8 shift;
>  	u8 width;
> +	unsigned int factor;
>  };
>  
>  struct ccu_mix {
> @@ -130,10 +131,11 @@ static struct ccu_mix _name = {							\
>  }
>  
>  #define CCU_DIV_GATE_DEFINE(_name, _parent, _reg_ctrl, _shift, _width,		\
> -			    _mask_gate,	_flags)					\
> +			    _mask_gate,	_factor, _flags)			\

This isn't that consistent: why could only divider-gate come with a
factor? This is another reason why I think representing the factor
separately with the CCU_FACTOR_DEFINE() macro is better.

>  static struct ccu_mix _name = {							\
>  	.gate	= CCU_GATE_INIT(_mask_gate),					\
>  	.div	= CCU_DIV_INIT(_shift, _width),					\
> +	.div.factor = _factor,						\
>  	.common = {								\
>  		.reg_ctrl	= _reg_ctrl,					\
>  		CCU_MIX_INITHW(_name, _parent, spacemit_ccu_div_gate_ops,	\
> 
> -- 
> 2.50.1
> 

Best regards,
Haylen Chu