On Thu, Jul 21, 2016 at 11:52:15AM +0200, Ondřej Jirman wrote:

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If so, then yes, trying to switch to the 24MHz oscillator before
applying the factors, and then switching back when the PLL is stable
would be a nice solution.

I just checked, and all the SoCs we've had so far have that
possibility, so if it works, for now, I'd like to stick to that.

It would need to be tested. U-boot does the change only once, while the
kernel would be doing it all the time and between various frequencies
and PLL settings. So the issues may show up with this solution too.

That would have the benefit of being quite easy to document, not be a
huge amount of code and it would work on all the CPUs PLLs we have so
far, so still, a pretty big win. If it doesn't, of course, we don't
really have the choice.

It's probably more code though. It has to access different register from
the one that is already defined in dts, which would add a lot of code
and require dts changes. The original patch I sent is simpler than that.

Why?

You can use container_of to retrieve the parent structure of the clock
notifier, and then you get a ccu_common structure pointer, with the
CCU base address, the clock register, its lock, etc.

Look at what is done in drivers/clk/meson/clk-cpu.c. It's like 20 LoC.

I don't really get why anything should be changed in the DT, or why it
would add a lot of code. Or maybe we're not talking about the same
thing?

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com