[U-Boot-Users] flat tree clock setting

Timur Tabi timur at freescale.com
Thu Nov 9 22:23:46 CET 2006

Scott Wood wrote:

> Are there any boards on which OF_TBCLK is (properly) set to something 
> other than what get_tbclk() returns (ignoring the difference in 
> rounding)?  

A search of the source code shows this:

File /temp/u-boot-83xx/include/configs/MPC8349EMDS.h
   332 2:#define OF_TBCLK		(bd->bi_busfreq / 4)
File /temp/u-boot-83xx/include/configs/MPC8349ITX.h
   395 2:#define OF_TBCLK		(bd->bi_busfreq / 4)
File /temp/u-boot-83xx/include/configs/MPC8360EMDS.h
   327 2:#define OF_TBCLK		(bd->bi_busfreq / 4)
File /temp/u-boot-83xx/include/configs/MPC8540ADS.h
   309 2:#define OF_TBCLK		(bd->bi_busfreq / 8)
File /temp/u-boot-83xx/include/configs/MPC8541CDS.h
   320 2:#define OF_TBCLK		(bd->bi_busfreq / 8)
File /temp/u-boot-83xx/include/configs/MPC8548CDS.h
   326 2:#define OF_TBCLK		(bd->bi_busfreq / 8)
File /temp/u-boot-83xx/include/configs/MPC8555CDS.h
   320 2:#define OF_TBCLK		(bd->bi_busfreq / 8)
File /temp/u-boot-83xx/include/configs/MPC8560ADS.h
   302 2:#define OF_TBCLK		(bd->bi_busfreq / 8)
File /temp/u-boot-83xx/include/configs/MPC8641HPCN.h
   269 2:#define OF_TBCLK	(bd->bi_busfreq / 4)
File /temp/u-boot-83xx/include/configs/stxxtc.h
   587 2:#define OF_TBCLK		(MPC8XX_HZ / 16)

Let's ignore the stxxtc for now, whatever that is.

On the 83xx, get_tbclk() returns "(gd->bus_clk + 3L) / 4L".  On 85xx and 86xx, 
it does this:

	return ((sys_info.freqSystemBus + 7L) / 8L);

sys_info.freqSystemBus can be any number of things (see get_sys_info).

Well, it looks like they COULD always contain the same value.

> I don't see any, nor can I think of a reason why such a 
> difference should ever exist.  Perhaps OF_TBCLK should just be removed?

I think it's safe to say that *something* is redundant here, but I don't know 
yet what.  My vote would be for OF_TBCLK, though, if that works.

The only thing I know for sure is that all of this clock stuff is making me 

Timur Tabi
Linux Kernel Developer @ Freescale

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