linux-kernel - Re: [PATCH][POWERPC] Workaround for iommu page alignment

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Message-Id: <1199745684.7518.25.camel@concordia>
Date:	Tue, 08 Jan 2008 09:41:24 +1100
From:	Michael Ellerman <michael@...erman.id.au>
To:	benh@...nel.crashing.org
Cc:	Paul Mackerras <paulus@...ba.org>,
	linuxppc-dev list <linuxppc-dev@...abs.org>,
	Linux Kernel list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH][POWERPC] Workaround for iommu page alignment

On Tue, 2008-01-08 at 08:45 +1100, Benjamin Herrenschmidt wrote:
> Our iommu page size is currently always 4K. That means with our current
> code, drivers may do a dma_map_sg() of a 64K page and obtain a dma_addr_t
> that is only 4K aligned.
> 
> This works fine in most cases except some infiniband HW it seems, where
> they tell the HW about the page size and it ignores the low bits of the
> DMA address.
> 
> This works around it by making our IOMMU code enforce a PAGE_SIZE alignment
> for mappings of objects that are page aligned in the first place and whose
> size is larger or equal to a page.
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

I don't see in the code where you implement the "size > PAGE_SIZE"
condition. But I only just got back from holidays .. :)

cheers

-- 
Michael Ellerman
OzLabs, IBM Australia Development Lab

wwweb: http://michael.ellerman.id.au
phone: +61 2 6212 1183 (tie line 70 21183)

We do not inherit the earth from our ancestors,
we borrow it from our children. - S.M.A.R.T Person

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