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

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Message-ID: <4171d9d6-1f2c-44d3-b908-3ca11ffa9d96@collabora.com>
Date: Thu, 5 Feb 2026 12:43:44 +0100
From: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
To: Stephen Boyd <sboyd@...nel.org>,
 Michael Turquette <mturquette@...libre.com>
Cc: 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>,
 Brian Masney <bmasney@...hat.com>, Chen-Yu Tsai <wenst@...omium.org>
Subject: Re: [PATCH] Revert "clk: Respect CLK_OPS_PARENT_ENABLE during recalc"

Il 03/02/26 01:24, Stephen Boyd ha scritto:
> 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>

Makes sense, and I agree.

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>