[U-Boot] AM335x PLL configuration

[U-Boot] AM335x PLL configuration

[Mark Jackson]

All the current TI AM335x boards currently appear to start with an MPU clock of 550MHx and a core clock of 1GHz,
based on #defines in include/asm/arch-am33xx/clocks_am33xx.h

I assume most people then pass control over to (eg) cpufreq once Linux boots.

However I would like to just boot up at the max clock speed (i.e. 720MHz).

Is there any merit in reworking this to allow the clock speeds to be specified in the config heaeder file ?

Or would it be better to allow the board init code to adjust the clock settings "on-the-fly" ?

I could just add some extra code to my own board.c file, but that doesn't seem like a very elegant solution !!

Maybe someone else already has a solution for this ?

Cheers
Mark J.

[U-Boot] AM335x PLL configuration

[Tom Rini]

On Sat, Feb 23, 2013 at 11:45:45AM +0000, Mark Jackson wrote:

> All the current TI AM335x boards currently appear to start with an MPU clock of 550MHx and a core clock of 1GHz,
> based on #defines in include/asm/arch-am33xx/clocks_am33xx.h
> 
> I assume most people then pass control over to (eg) cpufreq once Linux boots.
> 
> However I would like to just boot up at the max clock speed (i.e. 720MHz).
> 
> Is there any merit in reworking this to allow the clock speeds to be specified in the config heaeder file ?
> 
> Or would it be better to allow the board init code to adjust the clock settings "on-the-fly" ?
> 
> I could just add some extra code to my own board.c file, but that doesn't seem like a very elegant solution !!
> 
> Maybe someone else already has a solution for this ?

The "vendor" tree has a partial solution for this, which is to make the
initial speed be the safe value (550MHz) and then if we can, depending
on board, run the clock up.  For example, Beaglebone can be USB bus
powered or wall-powered, but it's only safe to run up to 720MHz (due to
potenital power spikes later on during kernel boot) if on wall power.

So yes, if you want to start down the road of allowing boards to say "I
know I can now run at ...", please do so!

-- 
Tom
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