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RE: Problems booting Linux 2.6.18.1 on MIPS34K core

To: "'Atsushi Nemoto'" <anemo@mba.ocn.ne.jp>
Subject: RE: Problems booting Linux 2.6.18.1 on MIPS34K core
From: Trevor Hamm <Trevor_Hamm@pmc-sierra.com>
Date: Wed, 15 Nov 2006 15:09:34 -0800
Cc: linux-mips@linux-mips.org
Original-recipient: rfc822;linux-mips@linux-mips.org
Sender: linux-mips-bounce@linux-mips.org
 

> -----Original Message-----
> From: linux-mips-bounce@linux-mips.org 
> [mailto:linux-mips-bounce@linux-mips.org] On Behalf Of Atsushi Nemoto
> Sent: Wednesday, November 15, 2006 8:07 AM
> To: Trevor Hamm
> Cc: linux-mips@linux-mips.org
> Subject: Re: Problems booting Linux 2.6.18.1 on MIPS34K core
> 
> Then, I can imagine three (hardly possible) case:
> 
> A.  PG_dcache_dirty bit was cleared accidently.
> 
> B.  The page is accessed by user process without page_mapping()
> 
> C.  kernel forgot to call update_mmu_cache() at somewhere.
> 
> If case A, removing "&& Page_dcache_dirty(page)" condition from
> __update_cache() will hide your problem.  If case B, calling
> flush_dcache_page() unconditionally in __update_cache() will hide your
> problem.
> 
> Anyway for now I can not see why this can happen...
> 

Okay, so after writing up that long explanation, reading through some more 
kernel code, and re-reading what you wrote above, I realize that all I've done 
was to verify what you've already suspected all along -- that a 
flush_dcache_page on this page somehow doesn't flush the page.  This is my 
first time studying the cache/memory management code in Linux 2.6; thanks for 
being so patient with me :-)

I tried the remedies you suggested for Case A and B, but neither one produces a 
kernel which can boot from power-up.  So far, the only work-around that works 
is calling flush_data_cache_page unconditionally from __flush_dcache_page.  
This would imply that Case C is the culprit.  I'll see what I can do to verify 
this.

Thanks,
Trevor

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