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From: Arnd Bergmann <arnd@arndb.de>
To: michael@ellerman.id.au
Subject: Re: [Cbe-oss-dev] [patch 11/11] powerpc/cell: Add
	DMA_ATTR_STRONG_ORDERING dma attribute and use in IOMMU code
Date: Mon, 7 Jul 2008 11:01:24 +0200
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Cc: Paul Mackerras <paulus@samba.org>, cbe-oss-dev@ozlabs.org,
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On Monday 07 July 2008, Michael Ellerman wrote:
> 
> > It turned out that the firmware sets up the south bridge to never set the 'S'
> > bit on incoming transactions, which overrides the IOPTE_SO_RW bits, on all
> > existing cell hardware.
> 
> It seems strange to me that the southbridge is allowed to override the
> setting in the IOMMU page table, but if that's what the doc says ..

That's what I thought at first as well, but it actually makes sense:
If the bridge knows that a data packet has been reordered already
by the originator or one of its own busses, there is no point in
enforcing strong ordering at the IOMMU again.

	Arnd <><