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IP22 64bit kernel

To: linux-mips@linux-mips.org
Subject: IP22 64bit kernel
From: tsbogend@alpha.franken.de (Thomas Bogendoerfer)
Date: Tue, 11 Sep 2007 23:30:48 +0200
Original-recipient: rfc822;linux-mips@linux-mips.org
Sender: linux-mips-bounce@linux-mips.org
User-agent: Mutt/1.5.13 (2006-08-11)
I finally figured out, why 64bit SGI IP22 kernels are broken (at
least when booted with SGI sash). Looks like sash jumps to an uncached
XPHYS address instead of the KSEG0 address indicated by the ELF start.
This messes up bogomips calculation.

I found an interesting piece of code in head.S:

        .macro  ARC64_TWIDDLE_PC
#if defined(CONFIG_ARC64) || defined(CONFIG_MAPPED_KERNEL)
        /* We get launched at a XKPHYS address but the kernel is linked
 * to
           run at a KSEG0 address, so jump there.  */
        PTR_LA  t0, \@f
        jr      t0
\@:
#endif
        .endm


Enabling this for (CONFIG_SGI_IP22 && CONFIG_64BIT) fixes the boot problem.
It's not big deal to add this, but I'm wondering why we not just always
use this macro ? What platforms do it break with it ?

Thomas.
 
-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessary a
good idea.                                                [ RFC1925, 2.3 ]

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