Re: [PATCH v2] clk: meson: Fix the determine rate error in clk_regmap_divider_ro_ops

[Neil Armstrong <neil.armstrong@linaro.org>]

On 12/11/2024 13:57, Chuan Liu via B4 Relay wrote:
> From: Chuan Liu <chuan.liu@amlogic.com>
> 
> The rate determined by calling clk_regmap_divider_ro_ops with
> clk_regmap_div_determine_rate is not RO, which will result in the
> unexpected modification of the frequency of its children when setting
> the rate of a clock that references clk_regmap_divider_ro_ops.
> 
> Fiexs: ea11dda9e091 ("clk: meson: add regmap clocks")
> Signed-off-by: Chuan Liu <chuan.liu@amlogic.com>
> ---
> Background: During the execution of clk_set_rate(), the function
> clk_core_round_rate_nolock() is called to calculate the matching rate
> and save it to 'core->new_rate'. At the same time, it recalculates and
> updates its 'child->newrate'. Finally, clk_change_rate() is called to
> set all 'new_rates'.
> ---
> Changes in v2:
> - Remove the CLK_DIVIDER_READ_ONLY judgment logic in
> clk_regmap_div_determine_rate().
> - Add clk_regmap_div_ro_determine_rate().
> - Link to v1: https://lore.kernel.org/r/20241111-fix_childclk_of_roclk_has_been_tampered_with-v1-1-f8c1b6ffdcb0@amlogic.com
> ---
>   drivers/clk/meson/clk-regmap.c | 36 ++++++++++++++++++++----------------
>   1 file changed, 20 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/clk/meson/clk-regmap.c b/drivers/clk/meson/clk-regmap.c
> index 07f7e441b916..edf65ca92c7a 100644
> --- a/drivers/clk/meson/clk-regmap.c
> +++ b/drivers/clk/meson/clk-regmap.c
> @@ -80,21 +80,6 @@ static int clk_regmap_div_determine_rate(struct clk_hw *hw,
>   {
>   	struct clk_regmap *clk = to_clk_regmap(hw);
>   	struct clk_regmap_div_data *div = clk_get_regmap_div_data(clk);
> -	unsigned int val;
> -	int ret;
> -
> -	/* if read only, just return current value */
> -	if (div->flags & CLK_DIVIDER_READ_ONLY) {

You're breaking current code by no more checking this flag,
the new clk_regmap_div_ro_determine_rate() is fine, but you should call
it from here if CLK_DIVIDER_READ_ONLY is set.

Neil

> -		ret = regmap_read(clk->map, div->offset, &val);
> -		if (ret)
> -			return ret;
> -
> -		val >>= div->shift;
> -		val &= clk_div_mask(div->width);
> -
> -		return divider_ro_determine_rate(hw, req, div->table,
> -						 div->width, div->flags, val);
> -	}
>   
>   	return divider_determine_rate(hw, req, div->table, div->width,
>   				      div->flags);
> @@ -127,9 +112,28 @@ const struct clk_ops clk_regmap_divider_ops = {
>   };
>   EXPORT_SYMBOL_NS_GPL(clk_regmap_divider_ops, CLK_MESON);
>   
> +static int clk_regmap_div_ro_determine_rate(struct clk_hw *hw,
> +					    struct clk_rate_request *req)
> +{
> +	struct clk_regmap *clk = to_clk_regmap(hw);
> +	struct clk_regmap_div_data *div = clk_get_regmap_div_data(clk);
> +	unsigned int val;
> +	int ret;
> +
> +	ret = regmap_read(clk->map, div->offset, &val);
> +	if (ret)
> +		return ret;
> +
> +	val >>= div->shift;
> +	val &= clk_div_mask(div->width);
> +
> +	return divider_ro_determine_rate(hw, req, div->table, div->width,
> +					 div->flags, val);
> +}
> +
>   const struct clk_ops clk_regmap_divider_ro_ops = {
>   	.recalc_rate = clk_regmap_div_recalc_rate,
> -	.determine_rate = clk_regmap_div_determine_rate,
> +	.determine_rate = clk_regmap_div_ro_determine_rate,
>   };
>   EXPORT_SYMBOL_NS_GPL(clk_regmap_divider_ro_ops, CLK_MESON);
>   
> 
> ---
> base-commit: 664988eb47dd2d6ae1d9e4188ec91832562f8f26
> change-id: 20241111-fix_childclk_of_roclk_has_been_tampered_with-61dbcc623746
> 
> Best regards,