linux-kernel - Re: [PATCH][POWERPC] Workaround for iommu page alignment (#2)

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Date:	Mon, 7 Jan 2008 21:48:24 -0600
From:	Olof Johansson <olof@...om.net>
To:	Benjamin Herrenschmidt <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 (#2)

On Tue, Jan 08, 2008 at 10:34:22AM +1100, Benjamin Herrenschmidt wrote:
> powerpc: Workaround for iommu page alignment
> 
> 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.
> 
> Signed-off-by: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> ---
> 
> And this version actually does what the comment says (I had forgotten
> to quilt ref... a common mistake).

And sloppy of me to not catch it. Anyway:

Acked-by: Olof Johansson <olof@...om.net>

I wonder how long until there's a device that has some other < PAGE_SIZE
alignment bug^Wrequirement that we'll need to meet too. :(


-Olof

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