Re: TS 7200 kernel image size

[Jason Thorpe <thorpej%shagadelic.org@localhost>]

On May 5, 2009, at 2:06 AM, Lloyd Parkes wrote:

> I$ seems to be on, although it sure feels like it's off when using a  
> gzimg. Maybe the RedBoot go command switches it off (unlikely), or  
> the gzimg switches it off so that it doesn't have to manage it (more  
> likely)?

One might say that I was taking the easy way out when I wrote gzboot.   
See sys/arch/evbarm/stand/gzboot/srtbegin.S:

ENTRY(start)
        /*
         * We assume we've been loaded VA==PA, or that the MMU
         * is disabled.  Make sure the MMU is disabled so that
         * we don't have to care about the caches.
         */
        mrc     p15, 0, r2, c1, c0, 0
        bic     r2, r2, #CPU_CONTROL_MMU_ENABLE
        mcr     p15, 0, r2, c1, c0, 0

        nop
        nop
        nop


Of course, if the MMU is off, you don't get caches on < ARMv6 (and I  
don't know about ARMv6 because I've never done any low-level work on  
one) because they're all virtually-indexed, etc.

gzboot relocates itself out of flash and into RAM (well, this is  
configurable in the Makefile/ldscript per board), so you could always  
add a board-specific setup hook that mapped RAM VA==PA and turned on  
the MMU, I$, and D$.  That would probably provide a ... monumental  
speed-up.

OF course, before jumping into the kernel, you'd want to flush /  
disable the caches and MMU in another board-specific hook.

This means that you'd have to add processor-specific routines to  
evbarm/stand for managing the cache, but that probably wouldn't be  
that big of a deal.

> Cheers,
> Lloyd

-- thorpej