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

[Ulf Hansson]

On 7 September 2012 23:59, Mike Turquette <mturquette at linaro.org> wrote:
> Quoting Ulf Hansson (2012-09-07 06:26:21)
>> On 7 September 2012 14:40, Shawn Guo <shawn.guo at 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?
>

The value for smp_twd clock freq is not directly connected to the CPU
freq clock, I believe. I will dig into the details to see what we can
do to make the most easiest solution.
Using a "parent" solution is definitely to prefer, so let's see.

Kind regards
Ulf Hansson