Re: [PATCH] clk: mediatek: Export CPU mux clocks for CPU frequency control

[Sascha Hauer <s.hauer@pengutronix.de>]

On Tue, Mar 10, 2015 at 09:53:19AM +0800, Pi-Cheng Chen wrote:
> On 5 March 2015 at 15:42, Sascha Hauer <s.hauer@pengutronix.de> wrote:
> >
> > My suggestion is to take another approach. Implement clk_set_rate for
> > these muxes and in the set_rate hook:
> >
> > - switch mux to intermediate PLL parent
> > - call clk_set_rate() for the real parent PLL
> > - switch mux back to real parent PLL
> 
> Hi Sascha,
> 
> Thanks for your suggestion. I've tried to take this approach, but there's some
> issues here.
> 
> Calling clk_set_rate() inside the set_rate callback of cpumux will cause
> an infinite recursive calling in the clock framework:
> mux.set_rate() -> pll.set_rate() -> mux.set_rate -> ...

I don't understand why setting the PLL rate should call into the mux
set_rate. Are you sure you call clk_set_rate for the mux parent clk?
I think the general approach should work, drivers/clk/sirf/clk-common.c
does something similar in cpu_clk_set_rate(). If you like you can send
me your work in progress state privatly, I'll have a look then.

> 
> I've also tries to update pll register settings in the set_rate()
> callback of cpumux,
> but the PLL clock information will not be correctly updated in this case.

No, that won't work.

Sascha


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