linux-kernel - Re: [PATCH]: PCI: GART iommu alignment fixes [v2]

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Message-ID: <20080723221033.GD13662@8bytes.org>
Date:	Thu, 24 Jul 2008 00:10:33 +0200
From:	Joerg Roedel <joro@...tes.org>
To:	Prarit Bhargava <prarit@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	jbarnes@...tuousgeek.org, fujita.tomonori@....ntt.co.jp
Subject: Re: [PATCH]: PCI: GART iommu alignment fixes [v2]

On Wed, Jul 23, 2008 at 07:19:43AM -0400, Prarit Bhargava wrote:
> pci_alloc_consistent/dma_alloc_coherent does not return size aligned
> addresses.
> 
> >From Documentation/DMA-mapping.txt:
> 
> "pci_alloc_consistent returns two values: the virtual address which you
> can use to access it from the CPU and dma_handle which you pass to the
> card.
> 
> The cpu return address and the DMA bus master address are both
> guaranteed to be aligned to the smallest PAGE_SIZE order which
> is greater than or equal to the requested size.  This invariant
> exists (for example) to guarantee that if you allocate a chunk
> which is smaller than or equal to 64 kilobytes, the extent of the
> buffer you receive will not cross a 64K boundary."

Interesting. Have you experienced any problems because of that
misbehavior in the GART code? AMD IOMMU currently also violates this
requirement. I will send a patch to fix that there too.

Joerg

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