[U-Boot-Users] PPC CLKIN

Kumar Gala galak at kernel.crashing.org
Thu Mar 9 04:27:56 CET 2006

On Mar 8, 2006, at 5:49 PM, Wolfgang Denk wrote:

> In message  
> <1628E43D99629C46988BE46087A3FBB94B48E7 at ep-01.EmbeddedPlanet.local>  
> you wrote:
>> We currently have several PQII and PQIII PrPMC boards that  
>> dynamically
>> support PCI bus speeds between 25 MHz and 133 MHz. These boards  
>> provide
>> a CPLD register that gives PCI frequency. I would like to take  
>> advantage
>> of this register, if possible, within u-boot rather than using a  
>> #define
>> such as CONFIG_83XX_CLKIN, CONFIG_8260_CLKIN, or  
>> the input clock frequency to the processor. Is there a suggested  
>> method
>> of doing this?
> Yes: don't change the code if there is no reeal need for it.
>> For testing I have implemented the following in get_sys_info() in
>> speed.c for an MPC8560 board:
>> #if !defined (CONFIG_SYS_CLK_FREQ)
>> 	sysInfo->freqSystemBus = plat_ratio * get_sys_clk();
>> #else
>> 	sysInfo->freqSystemBus = plat_ratio * CONFIG_SYS_CLK_FREQ;
>> #endif
> A simple "#define  CONFIG_SYS_CLK_FREQ  get_sys_clk()"  seems  to  be
> equivalent  without need to change anything. Note that I didn't check
> all uses of the CONFIG_SYS_CLK_FREQ variable in the code.
>> The get_sys_clk() function resides in the board code directory. Would
>> this be an acceptable method? It would minimize any impact to other
>> existing boards.
> What about my suggestion?

This should work.  It is how the CDS platform works.  Take a look at  
board/cds/common/cadmus.c and include/configs/*CDS*.h

- kumar

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