cpufreq / UPLL (was Re: [PATCH 0/9] Experimental S3C2410A cpufreq driver)

Harald Welte laforge at openmoko.org
Wed Feb 13 03:06:11 CET 2008

On Wed, Feb 13, 2008 at 02:58:57AM +0100, Harald Welte wrote:
> Both Sound and USB derive their clocks from the UPLL, not the MPLL. USB
> depends on a 48MHz clock in order to operate at all.
> So unless we suspend to RAM, I think the UPLL should be kept running at
> its original speed.  cpufreq should only touch MPLL.

well, theoretically the UPLL could be shut down / slowed down if we are
absolutely sure we don't need any USB, i.e. if bluetooth is not used,
nothing plugged into the USB jack, and no audio is used.  This is
complex (especially the bluetooth part, since powering up would
basically mean to re-enumerate the USB) and I also believe that it's not
going to save all that much power...

- Harald Welte <laforge at openmoko.org>          	        http://openmoko.org/
Software for the world's first truly open Free Software mobile phone

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