linux-kernel - Re: [PATCH] Revert "clk: Respect CLK_OPS_PARENT

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Message-ID: <6238918.lOV4Wx5bFT@steina-w>
Date: Tue, 03 Feb 2026 08:32:03 +0100
From: Alexander Stein <alexander.stein@...tq-group.com>
To: Michael Turquette <mturquette@...libre.com>,
 Stephen Boyd <sboyd@...nel.org>, Stephen Boyd <sboyd@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org,
 patches@...ts.linux.dev, Mark Brown <broonie@...nel.org>,
 Nicolas Frattaroli <nicolas.frattaroli@...labora.com>,
 Brian Masney <bmasney@...hat.com>,
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
 Chen-Yu Tsai <wenst@...omium.org>
Subject: Re: [PATCH] Revert "clk: Respect CLK_OPS_PARENT_ENABLE during recalc"

Am Dienstag, 3. Februar 2026, 01:24:38 CET schrieb Stephen Boyd:
> This reverts commit 669917676e93fca5ea3c66fc9539830312bec58e.
> It's been shown to cause problems on i.MX and STM32 platforms
> where the board doesn't boot. In one case, a clk with
> CLK_IS_CRITICAL and CLK_OPS_PARENT_ENABLE is being registered
> causing the parent to be enabled, the rate recalculated, and then
> the parent is disabled causing the critical clk being registered
> to stop clocking.
> 
> A fix for that would be to calculate the rate of the clk after
> enabling the critical clk itself, but that wouldn't fix another
> problem where a clk with CLK_OPS_PARENT_ENABLE is registered
> before the parent is registered. In this case the hardware access
> in the clk_ops::recalc_rate() function would fail if the parent
> is disabled.
> 
> There are even more problems exposed by this patch because it
> introduces logic that disables clks earlier in system boot than
> has existed previously. Historically we've not disabled clks
> until late init (clk_disable_unused) under the assumption that
> clks have been registered enough to have a consistent view of the
> clk tree. The clk_disable_unused logic doesn't work very well
> though, leading to quite a few devices booting with
> clk_ignore_unused on the kernel command line.
> 
> Long story short, disabling clks during clk registration is full
> of pitfalls. Revert this commit until a proper solution can be
> found.
> 
> Reported-by: Alexander Stein <alexander.stein@...tq-group.com>
> Closes: https://lore.kernel.org/r/6239343.lOV4Wx5bFT@steina-w
> Reported-by: Mark Brown <broonie@...nel.org>
> Closes: https://lore.kernel.org/r/036da7ce-6487-4a6e-9b15-97c6d3bcdcec@sirena.org.uk
> Cc: Nicolas Frattaroli <nicolas.frattaroli@...labora.com>
> Cc: Brian Masney <bmasney@...hat.com>
> Cc: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
> Cc: Chen-Yu Tsai <wenst@...omium.org>
> Signed-off-by: Stephen Boyd <sboyd@...nel.org>

Tested-by: Alexander Stein <alexander.stein@...tq-group.com>

> ---
>  drivers/clk/clk.c | 13 -------------
>  1 file changed, 13 deletions(-)
> 
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index 1b0f9d567f48..85d2f2481acf 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -1921,14 +1921,7 @@ 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;
> @@ -4038,9 +4031,6 @@ static int __clk_core_init(struct clk_core *core)
>  	 */
>  	clk_core_update_duty_cycle_nolock(core);
>  
> -	if (core->flags & CLK_OPS_PARENT_ENABLE)
> -		clk_core_prepare_enable(core->parent);
> -
>  	/*
>  	 * Set clk's rate.  The preferred method is to use .recalc_rate.  For
>  	 * simple clocks and lazy developers the default fallback is to use the
> @@ -4056,9 +4046,6 @@ static int __clk_core_init(struct clk_core *core)
>  		rate = 0;
>  	core->rate = core->req_rate = rate;
>  
> -	if (core->flags & CLK_OPS_PARENT_ENABLE)
> -		clk_core_disable_unprepare(core->parent);
> -
>  	/*
>  	 * Enable CLK_IS_CRITICAL clocks so newly added critical clocks
>  	 * don't get accidentally disabled when walking the orphan tree and
> 
> base-commit: aa2ad19210a6a444111bce55e8b69579f29318fb
> 


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