Variable Clock Frequency and Power Saving
andy at openmoko.com
Wed Oct 29 03:28:34 CET 2008
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Somebody in the thread at some point said:
| I put together a cpuidle driver for the S3C2410 and added the
| NO_HZ/clockevents work from Andresz to my build. What follows is a
| list of time spent in idle (that's S3C2410 mode IDLE) for my GTA01.
| Some of the long idle times are really impressive (almost 0.5
| Anyway, the point of this post is to see what is happening in
| powersaving work. I had a look at adding an idle-mode that switches
| to SLOW mode; this might be feasible, but as so many drivers need to
| adjust to the change of clock rate, the time to enter and leave this
| idle mode becomes significant (although, for 0.5 seconds, it should be
| no problem).
Thanks for looking at this area. 500mS chunks in SLOW or some strong
powersaving mode wth short wakes before the next one is pretty serious
| That said, there is no support for clock rate adjustment at all right
| now. Is somebody working on this or does this already work in
| somebody's tree somewhere?
Cesar has cpufreq patches for GTA01, Ben Dooks mentioned them by name
when I met him and he seemed interested to take them upstream. I saw
the odd cpufreq reference in s3c arch stuff in stable-tracking, but when
I went to grep it I see they are not really doing anything yet.
| I think we need to adjust the 'clk' infrastructure so that:
| i) Children are notified when parent clock rate changes
| ii) Clocks can be reparented (for example, for SLOW mode we switch
| from MPLL to XTAL).
| iii) Clocks get a list of callbacks to invoke when their rate changes
| so that drivers can make the necessary adjustments. (e.g. framebuffer
| driver needs to know when hclk changes in order to adjust its vclk
I cc Ben and Cesar.
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