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Re: Problems booting Linux 2.6.18.1 on MIPS34K core

To: Trevor_Hamm@pmc-sierra.com
Subject: Re: Problems booting Linux 2.6.18.1 on MIPS34K core
From: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Date: Wed, 15 Nov 2006 23:06:33 +0900 (JST)
Cc: linux-mips@linux-mips.org
In-reply-to: <E8C8A5231DDE104C816ADF532E0639120194F4CD@bby1exm07.pmc_nt.nt.pmc-sierra.bc.ca>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <E8C8A5231DDE104C816ADF532E0639120194F4CD@bby1exm07.pmc_nt.nt.pmc-sierra.bc.ca>
Sender: linux-mips-bounce@linux-mips.org
On Tue, 14 Nov 2006 13:47:41 -0800, Trevor Hamm <Trevor_Hamm@pmc-sierra.com> 
wrote:
> > Could you confirm that removing whole "if (mapping ..." block from
> > __flush_dcache_page can hide your problem?
> 
> Yes, removing this block seems to hide the problem.  I can boot
> completely to a login prompt.

Thank you for testing.  So we can omit "missing fludh_dcache_page()" case.

> > Or if you changed a line in __update_cache():
> > 
> >     int exec = (vma->vm_flags & VM_EXEC) && !cpu_has_ic_fills_f_dc;
> > 
> > to
> > 
> >     int exec = 1;
> > 
> > then your problem still happen?
> 
> Yes, with this change, the boot-up problem persists.

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...

Just for confirm:
1. This can happen on latest lmo git tree or 2.6.19-rc5.
2. UP kernel.
3. No L2 cache.
4. icache and dcache are both virtually indexed and physically tagged.
All correct?

---
Atsushi Nemoto

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