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

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Message-ID: <aYIRHf1njCXmoswF@redhat.com>
Date: Tue, 3 Feb 2026 10:15:41 -0500
From: Brian Masney <bmasney@...hat.com>
To: Stephen Boyd <sboyd@...nel.org>
Cc: Michael Turquette <mturquette@...libre.com>,
	linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org,
	patches@...ts.linux.dev,
	Alexander Stein <alexander.stein@...tq-group.com>,
	Mark Brown <broonie@...nel.org>,
	Nicolas Frattaroli <nicolas.frattaroli@...labora.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"

On Mon, Feb 02, 2026 at 04:24:38PM -0800, Stephen Boyd wrote:
> 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>

Reviewed-by: Brian Masney <bmasney@...hat.com>