Re: [PATCH 0/3] clk: Add __clk_disable_unprepare_counts_only() and use this in simple[fb|drm]

[Brian Masney <bmasney@redhat.com>]

Hi Hans,

On Wed, May 27, 2026 at 11:48:08AM +0200, Hans de Goede wrote:
> 2) One option considered was detaching the simple-framebuffer driver later,
>    after the real display driver has had a chance to claim the clocks. But
>    this won't work in cases where the real display driver picks different
>    parent clocks then the boot firmware did and needs to reparent clocks.

Why won't that work in the case where different parent clocks are selected?
I'll describe a scenario below.

> 
>    Basically the goal is for things to behave as if the simple-framebuffer
>    driver was not there at all, because that leaves the hw in the state
>    the real display driver expects.

I think the deferred unbinding could have some potential here where
there is some kind of notification mechanism between simple-framebuffer
and the real drm driver. So:

- simple-framebuffer driver takes reference(s) to the clk(s).

- real drm driver eventually loads, takes reference(s) to the necessary
  clk(s).

- real drm driver sends a notification to simple-framebuffer that it's
  done, and has control.

- simple-framebuffer can unbind and release its references to the clks.

No clks will be shutdown prematurely in this scenario.

If the real drm driver needs a different parent, then presumably things
should be setup correctly, and simple-framebuffer can have the clocks
shut down when it calls clk_disable_unprepare(). If the real drm driver
needed those clks, then it should hold a reference to them.

I'm intentionally not going through how to do the notification mechanism
here.

Brian