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

Hans de Goede
2026-03-17T12:16:38Z

Hi,

On 17-Mar-26 13:14, 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.

Interesting, so maybe we need a new way flag to mark clocks as not to
be turned off when turning unused clocks off, which does not block
them getting disabled normally later ?

(I was under the mistaken impression this is what CLK_IS_CRITICAL did)

Regards,

Hans