Re: [PATCH v3 1/5] clk: Respect CLK_OPS_PARENT_ENABLE during recalc

[Brian Masney <bmasney@redhat.com>]

Hi Nicolas,

On Fri, Oct 10, 2025 at 10:47:09PM +0200, Nicolas Frattaroli wrote:
> When CLK_OPS_PARENT_ENABLE was introduced, it guarded various clock
> operations, such as setting the rate or switching parents. However,
> another operation that can and often does touch actual hardware state is
> recalc_rate, which may also be affected by such a dependency.
> 
> Add parent enables/disables where the recalc_rate op is called directly.
> 
> Fixes: fc8726a2c021 ("clk: core: support clocks which requires parents enable (part 2)")
> Fixes: a4b3518d146f ("clk: core: support clocks which requires parents enable (part 1)")
> Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
> Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
> Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
> ---
>  drivers/clk/clk.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index 85d2f2481acf360f0618a4a382fb51250e9c2fc4..1b0f9d567f48e003497afc98df0c0d2ad244eb90 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -1921,7 +1921,14 @@ static unsigned long clk_recalc(struct clk_core *core,
>  	unsigned long rate = parent_rate;
>  
>  	if (core->ops->recalc_rate && !clk_pm_runtime_get(core)) {
> +		if (core->flags & CLK_OPS_PARENT_ENABLE)
> +			clk_core_prepare_enable(core->parent);
> +
>  		rate = core->ops->recalc_rate(core->hw, parent_rate);
> +
> +		if (core->flags & CLK_OPS_PARENT_ENABLE)
> +			clk_core_disable_unprepare(core->parent);
> +
>  		clk_pm_runtime_put(core);
>  	}
>  	return rate;

clk_change_rate() has the following code:


        if (core->flags & CLK_OPS_PARENT_ENABLE)
                clk_core_prepare_enable(parent);

	...

        core->rate = clk_recalc(core, best_parent_rate);

	...

        if (core->flags & CLK_OPS_PARENT_ENABLE)
                clk_core_disable_unprepare(parent);

clk_change_rate() ultimately is called by various clk_set_rate
functions. Will that be a problem for the double calls to
clk_core_prepare_enable()?

Fanning this out to the edge further is going to make the code even
more complicated. What do you think about moving this to
clk_core_enable_lock()? I know the set_parent operation has a special
case that would need to be worked around.

Brian