[PATCH] ARM: smp_twd: reprogram twd based on clk notifier

[mturquette@linaro.org (Mike Turquette)]

Quoting Ulf Hansson (2012-09-07 06:26:21)
> On 7 September 2012 14:40, Shawn Guo <shawn.guo@linaro.org> wrote:
> > On Fri, Sep 07, 2012 at 01:59:40PM +0200, Ulf Hansson wrote:
> >> Hi Shawn and Mike,
> >>
> >> In general I am in favor of this patch, but I also see some
> >> corresponding problems to resolve. Please correct me if I am wrong.
> >>
> >> I suppose most machines is relying on that it enough to only take care
> >> of the notification by using "cpufreq_notify_transition" from their
> >> cpufreq drivers. Thus those have to make sure the updates for smp_twd
> >> clock is supported from within the cpufreq driver I suppose.
> >>
> >> In other words the cpufreq drivers needs to do clk_get of "smp_twd"
> >> clock and then do a set_rate on it when it's has changed, to trigger a
> >> rate change notification. Is this what you also have in mind or do you
> >> have any other idea of how this should work?
> >>
> > Here is how it works on imx6q.
> >
> > 1) There are clks arm and twd defined in imx6q clock tree.  And twd
> >    is registered to clock framework as one child of arm clk with a fixed
> >    divider 2.
> >
> >         /*                                    name         parent_name     mult div */
> >         clk[twd]       = imx_clk_fixed_factor("twd",       "arm",            1, 2);
> >
> > 2) Register lookup "cpu0" and "smp_twd" for cpufreq and smp_twd drivers
> >    respectively.
> >
> >         clk_register_clkdev(clk[twd], NULL, "smp_twd");
> >         clk_register_clkdev(clk[arm], NULL, "cpu0");
> >
> > That's it.  The clock framework will just handle all the work nicely.
> > When cpufreq driver scales arm clk, the framework will propagate the
> > rate change to twd clk automatically.  And once twd clk rate changes,
> > smp_twd will get the notification.
> >
> 
> That's a nice solution!
> This won't work for ux500 that simple though. Maybe I might be able to
> use some kind of clock "parent" thing though, let's see. Thanks for
> the information!

Hi Ulf,

Why won't this work for ux500?

Thanks,
Mike

> 
> Kind regards
> Ulf Hansson
> 
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