linux-kernel - Re: [PATCH v3 1/5] clk: Respect CLK_OPS_PARENT

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Message-ID: <aPFbDl_JKyDay1S5@redhat.com>
Date: Thu, 16 Oct 2025 16:52:30 -0400
From: Brian Masney <bmasney@...hat.com>
To: Nicolas Frattaroli <nicolas.frattaroli@...labora.com>
Cc: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...nel.org>,
	Dong Aisheng <aisheng.dong@....com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	Yassine Oudjana <y.oudjana@...tonmail.com>,
	Laura Nao <laura.nao@...labora.com>,
	Nícolas F. R. A. Prado <nfraprado@...labora.com>,
	Chia-I Wu <olvaffe@...il.com>, Chen-Yu Tsai <wenst@...omium.org>,
	kernel@...labora.com, linux-clk@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH v3 1/5] clk: Respect CLK_OPS_PARENT_ENABLE during recalc

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@...labora.com>
> Reviewed-by: Chen-Yu Tsai <wenst@...omium.org>
> Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@...labora.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