[PATCH 0/9] Experimental S3C2410A cpufreq driver

Harald Welte laforge at openmoko.org
Wed Feb 13 02:58:57 CET 2008

On Tue, Feb 12, 2008 at 11:23:42PM -0200, Cesar Eduardo Barros wrote:
> For some weeks I have been working on a cpufreq driver for the GTA01 (to  
> try to make its battery last a bit longer). It's far from complete (it  
> will end up touching almost every device driver for the SoC), but the  
> core code (which does the frequency switching) is mostly ready.

Thanks a lot, this is really a great contribution.

> Some characteristics of the S3C2410 are not well supported by the core  
> cpufreq architecture, meaning it had to be bent a bit to fit:

I think those issues should be adressed with Dave Jones (cpufreq
maintainer). It's probably a good idea to post the issues to the
cpufreq at lists.linux.org.uk list.

> The following drivers have already been adapted to work with the cpufreq  
> driver:

I think those driver changes should see some review by Ben Dooks
(S3C24xx platform maintainer).

> I plan to work next on the USB gadget driver (which not only has a  
> minimum required frequency according to the datasheet but also for some  
> reason misbehaves if in use during a frequency transition).

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.

Please note that there are some intrinsic dependencies, i.e. the Samsung
docs state that you should not set only one of the two PLLs, but always
both together.  I've ran into quite some strange problems.
Interestingly, for me setting the PLL's in the opposite order of what
samsung recommends worked better than the other way around.

> Comments and suggestions are welcome. More information on the correct  
> formula for the PLL lock time would also be good.

What exactly is your question with regard to the PLL lock time?  Maybe I
can help.

- 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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