Re: [PATCH] clk: meson: vid-pll-div: added meson_vid_pll_div_ops support to enable vid_pll_div to meet clock setting requirements, especially for late chip

[Jerome Brunet <jbrunet@baylibre.com>]

On Thu 23 Feb 2023 at 14:27, Yu Tu <yu.tu@amlogic.com> wrote:

Title is way too long, 75 char max

> The previous chip only provides "ro_ops" for the vid_pll_div clock,

The driver does. Other chip could use RW ops I suppose.

> which is not satisfied with the operation requirements of the later
> chip for this clock, so the ops that can be set for the clock is added.
>

What requirements ? What "late" chip ? all this is quite vague.

> Signed-off-by: Yu Tu <yu.tu@amlogic.com>
> ---
>  drivers/clk/meson/vid-pll-div.c | 59 +++++++++++++++++++++++++++++++++
>  drivers/clk/meson/vid-pll-div.h |  1 +
>  2 files changed, 60 insertions(+)
>
> diff --git a/drivers/clk/meson/vid-pll-div.c b/drivers/clk/meson/vid-pll-div.c
> index daff235bc763..e75fa6f75efe 100644
> --- a/drivers/clk/meson/vid-pll-div.c
> +++ b/drivers/clk/meson/vid-pll-div.c
> @@ -89,6 +89,65 @@ static unsigned long meson_vid_pll_div_recalc_rate(struct clk_hw *hw,
>  	return DIV_ROUND_UP_ULL(parent_rate * div->multiplier, div->divider);
>  }
>  
> +static int meson_vid_pll_div_determine_rate(struct clk_hw *hw,
> +					    struct clk_rate_request *req)
> +{
> +	unsigned long best = 0, now = 0;
> +	unsigned int i, best_i = 0;
> +
> +	for (i = 0 ; i < ARRAY_SIZE(vid_pll_div_table) ; ++i) {

It would be nice to actually describe how this vid pll work so we can
stop using precompute "magic" values and actually use the IP to its full
capacity.

> +		now = DIV_ROUND_CLOSEST_ULL(req->best_parent_rate *

This effectively stops rate propagation. That's not how determine_rate()
call back should work. Have a look a clk-divider.c and how it calls
clk_hw_round_rate().

> +					    vid_pll_div_table[i].multiplier,
> +					    vid_pll_div_table[i].divider);
> +		if (req->rate == now) {
> +			return 0;
> +		} else if (abs(now - req->rate) < abs(best - req->rate)) {
> +			best = now;
> +			best_i = i;
> +		}
> +	}
> +
> +	if (best_i < ARRAY_SIZE(vid_pll_div_table))
> +		req->rate = DIV_ROUND_CLOSEST_ULL(req->best_parent_rate *
> +						  vid_pll_div_table[best_i].multiplier,
> +						  vid_pll_div_table[best_i].divider);
> +	else

What is the point of this 'if' clause ?
It looks like the 'else' part is dead code. 

> +		req->rate = meson_vid_pll_div_recalc_rate(hw, req->best_parent_rate);
> +
> +	return 0;
> +}
> +
> +static int meson_vid_pll_div_set_rate(struct clk_hw *hw, unsigned long rate,
> +				      unsigned long parent_rate)
> +{
> +	struct clk_regmap *clk = to_clk_regmap(hw);
> +	struct meson_vid_pll_div_data *pll_div = meson_vid_pll_div_data(clk);
> +	int i;
> +
> +	for (i = 0 ; i < ARRAY_SIZE(vid_pll_div_table) ; ++i) {
> +		if (DIV_ROUND_CLOSEST_ULL(parent_rate * vid_pll_div_table[i].multiplier,
> +					  vid_pll_div_table[i].divider) == rate) {

This assumes the set_rate() is going to have a perfect match and
otherwise fail. You should not assume that. Have a look at clk-divider.c
for examples.

> +			meson_parm_write(clk->map, &pll_div->val, vid_pll_div_table[i].shift_val);
> +			meson_parm_write(clk->map, &pll_div->sel, vid_pll_div_table[i].shift_sel);
> +			break;
> +		}
> +	}
> +
> +	if (i >= ARRAY_SIZE(vid_pll_div_table)) {
> +		pr_debug("%s: Invalid rate value for vid_pll_div\n", __func__);
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
> +const struct clk_ops meson_vid_pll_div_ops = {
> +	.recalc_rate	= meson_vid_pll_div_recalc_rate,
> +	.determine_rate	= meson_vid_pll_div_determine_rate,
> +	.set_rate	= meson_vid_pll_div_set_rate,
> +};
> +EXPORT_SYMBOL_GPL(meson_vid_pll_div_ops);
> +
>  const struct clk_ops meson_vid_pll_div_ro_ops = {
>  	.recalc_rate	= meson_vid_pll_div_recalc_rate,
>  };
> diff --git a/drivers/clk/meson/vid-pll-div.h b/drivers/clk/meson/vid-pll-div.h
> index c0128e33ccf9..3ab729b85fde 100644
> --- a/drivers/clk/meson/vid-pll-div.h
> +++ b/drivers/clk/meson/vid-pll-div.h
> @@ -16,5 +16,6 @@ struct meson_vid_pll_div_data {
>  };
>  
>  extern const struct clk_ops meson_vid_pll_div_ro_ops;
> +extern const struct clk_ops meson_vid_pll_div_ops;
>  
>  #endif /* __MESON_VID_PLL_DIV_H */
>
> base-commit: 8a9fbf00acfeeeaac8efab8091bb464bd71b70ea