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

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Message-ID: <4887BDB0.3000806@redhat.com>
Date:	Wed, 23 Jul 2008 19:24:32 -0400
From:	Prarit Bhargava <prarit@...hat.com>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
CC:	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	jbarnes@...tuousgeek.org
Subject: Re: [PATCH]: PCI: GART iommu alignment fixes [v2]



FUJITA Tomonori wrote:
> On Wed, 23 Jul 2008 07:19:43 -0400
> Prarit Bhargava <prarit@...hat.com> 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."
>>
>> 1.  Modify alloc_iommu to allow for an alignment mask
>> 2.  Modify pci_gart_simple to return size-aligned values.
>> 3.  Fixup the alignment calculation in the iommu-helper code.
>>     
>
> Hmm, you don't fix anything in the helper code. You just use
> __ALIGN_MASK.
>
>   
Yeah -- I meant "fixup" as opposed to fix.

> And please don't use __ALIGN_MASK. You will notice that no one in
> mainline use __ALIGN_MASK. Andrew said that we should not.
>
> Ideally, we should use ALIGN here but the current code was accepted
> because it is pretty simple and we have an comment what we do here. So
> please let it alone.
>   

I'll resubmit shortly ...

P.
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