Re: [PATCH] clk: add new Kconfig to control default behavior of disabling unused clocks

Maxime Ripard
2026-03-17T13:15:53Z

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On Tue, Mar 17, 2026 at 02:14:25PM +0200, Abel Vesa wrote:
> On 26-03-17 08:30:24, Maxime Ripard wrote:
> > Hi,
> >
> > On Mon, Mar 16, 2026 at 06:33:45PM -0400, Brian Masney wrote:
> > > At the 2023 Linux Plumbers Conference in Richmond VA, there was a
> > > discussion about how large number of systems need to boot with
> > > clk_ignore_unused. Per the discussions at the conference, the existing
> > > behavior in the clk core is broken, and there is a desire to completely
> > > remove this functionality.
> >
> > Broken how?
> >
> > clk_ignore_unused is to a point where it's seriously cargo-culted and
> > documented as a silver bullet, when in reality it's just a debug tool
> > for broken drivers, and the driver must be fixed.
> >
> > But nobody is actually fixing it.
> >
> > See
> > https://fedoraproject.org/wiki/Changes/Automatic_DTB_selection_for_aarch64_EFI_systems#How_To_Test
> > for example. The affected clock could be marked as CLK_IS_CRITICAL, and
> > fedora wouldn't have to package anything, change anything, etc. But no,
> > the problem is clk_ignore_unused.
>
> Nope. Don't ever mark clocks as critical unless system crashes without
> them.
>
> Here is an example or why clocks cannot be marked as critical but need
> to be kept by the clk_ignore_unused: display driver probes later.
> If you mark it as critical you just made the clock stay enabled even
> when display is off.
>
> And this is just one example.

Then use CLK_IGNORE_UNUSED.

Maxime

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