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Date:	Tue, 17 Jul 2007 11:54:36 +0400
From:	"Gleb O. Raiko" <raiko@niisi.msk.ru>
Organization: NIISI RAN
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To:	Ralf Baechle <ralf@linux-mips.org>
CC:	Sergey Rogozhkin <rogozhkin@niisi.msk.ru>, kumba@gentoo.org,
	linux-mips@linux-mips.org
Subject: Re: O2 RM7000 Issues
References: <4687DCE2.8070302@gentoo.org> <468825BE.6090001@gmx.net> <50451.70.107.91.207.1183381723.squirrel@webmail.wesleyan.edu> <20070704152729.GA2925@linux-mips.org> <20070704192208.GA7873@linux-mips.org> <469B5C2E.5080905@niisi.msk.ru> <20070716123343.GA13439@linux-mips.org>
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Ralf,

Considering RM7k the latest kernel improperly sets some hazards. At 
least, mtc0_tlbw_hazard and tlbw_use_hazard shall contain 4 nops, not 2.

Also, there shall be 10 nops after modification of the K0 field of the 
config register. The suspicious place I see is in 
arch/mips/mm/c-r4k.c:coherency_setup():
	change_c0_config(CONF_CM_CMASK, CONF_CM_DEFAULT);

If the K0 field has the value different than CONF_CM_DEFAULT, we 
definitely need nops here and, I'm afraid, even the line shall be 
executed uncached.

Strictly speaking, manual doesn't clearly define the term 
"modification". I expect, if I write the same value in the K0 field, it 
doesn't consider "modification".

And I guess all boards with RM7k select DMA_NONCOHERENT. Otherwise, 
CONF_CM_DEFAULT will have a garbage in case of RM7k. Perhaps, it's worth
to select DMA_NONCOHERENT inside the "config CPU_RM7000" block.

Regards,
Gleb.