[PATCH 4/5] clk: Add flag to prevent frequency changes when walking subtrees

[Miquel Raynal]

Hi Stephen,

>> The idea is: if the flag is set, instead of accepting the new upstream
>> rate and recalculate the downstream rate based on a previously set
>> divider value, we change our divider value to match the same frequency
>> as before. But if we cannot, then we just keep the old way.
>> 
>
> The exclusive rate code could support this if it doesn't already do so.
> If you call clk_set_rate_exclusive(child, <constant rate>) followed by
> clk_set_rate(parent, <new rate>) the core code should try to keep the
> child at the constant rate, or fail the clk_set_rate() call on the
> parent. It should be possible to confirm this with some KUnit tests for
> clk_set_rate_exclusive(). Similarly, if another child, child_B, of the
> parent changes the parent rate, we should speculate the new rate of the
> child_A that's protected and fail if we can't maintain the rate. We need
> to start generating a list of clks that we operate a rate change on to
> support this though, because right now we rely on the stack to track the
> clks that we change the rate of.
>
> Initially we thought that we could do this with clk notifiers. That may
> work here, but I suspect it will be clunky to get working because clk
> notifiers operate on struct clk.

I see, thanks a lot for the feedback, I'll have a look.

Thanks,
Miquèl