Re: IP32 prom crashes due to __pa() funkiness

[Kumba <kumba@gentoo.org>]

Kumba wrote:
> 
> Initially, booting a straight git checkout on an IP32 will cause it to 
> prom crash, usually somewhere in between init_bootmem() and 
> init_bootmem_core().  I bisected git to trace this back to one of the 
> inital __pa() introduction patches from commit d4df6d4 (get ride of 
> CPHYSADDR()).  It actually appears that the actual commit that broke 
> things was 620a480 (Make __pa() aware of XKPHYS/CKSEG0 address mix for 
> 64 bit kernels).
> 
> The [short-term] fix highlighted by Ilya is to make __pa() 
> unconditionally be defined to "((unsigned long)(x) < CKSEG0 ? 
> PAGE_OFFSET : CKSEG0)"; Discovered by building IP32 with 
> CONFIG_BUILD_ELF64=n.
> 
> Normally, this shouldn't be possible, as CONFIG_BUILD_ELF64=n was 
> originally only allowed by using the old o64 hack, which has 
> subsequently died and been replaced with the newer -msym32 form.  As far 
> as I know, CONFIG_BUILD_ELF64 is apparently supposed to be removed at 
> some point in the future, since I believe it existed only for quirky 
> 64bit-in-32bit kernels for IP22 and more commonly, IP32.  From 2.6.17 
> onwards, I've been building IP32 kernels with CONFIG_BUILD_ELF64=y and 
> using gcc-4, and haven't had problems up until now.
> 
> Anyways, I'm not sure if this is an IP32-specific oddity or not 
> (probably is), but it needs the define highlighted above to work 
> properly.  Plain PAGE_OFFSET won't work for these machines.  Given the 
> same trick os -msym32 is used for the rare IP22 64bit kernel, I would 
> not be surprised if the same problem and fix both occur and work for 
> those machines as well.  Something to maybe test later, I suppose.
> 
> But for now, anyone got thoughts as to a sane workaround for this?  
> Perhaps some conditional tweaks in mach-ip32/*.h files somewheres, would 
> it be simpler to just switch to:
> 
> #if defined(CONFIG_64BIT) && (!defined(CONFIG_BUILD_ELF64) || 
> defined(CONFIG_SGI_IP32))
> 
> (assuming that IP22 doesn't need it; I'll find out later)

"Re-verify range to target, One ping only."


So, anyone got thoughts on this?

I've actually built and booted an SGI IP32 kernel using this logic in 
include/asm-mips/page.h, Line 135:

#if defined(CONFIG_64BIT) && (!defined(CONFIG_BUILD_ELF64) || 
(defined(CONFIG_SGI_IP32) || defined(CONFIG_SGI_IP22)))



--Kumba

-- 
Gentoo/MIPS Team Lead

"Such is oft the course of deeds that move the wheels of the world: small hands 
do them because they must, while the eyes of the great are elsewhere."  --Elrond