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Date: Fri, 2 Oct 2015 06:51:59 +0800
From: Wei Yang <weiyang@linux.vnet.ibm.com>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: Wei Yang <weiyang@linux.vnet.ibm.com>, benh@kernel.crashing.org,
 paulus@samba.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH] powerpc/iommu: use iommu_num_pages() to calculate the
 number of iommu page
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Reply-To: Wei Yang <weiyang@linux.vnet.ibm.com>
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On Thu, Oct 01, 2015 at 02:15:45PM +1000, Michael Ellerman wrote:
>On Thu, 2015-10-01 at 07:50 +0800, Wei Yang wrote:
>> Hmm... some comments on this one? like it or not?
>
>It sounds like it's fixing a bug, but you don't really say. Have you seen this
>fail in the wild?

Hmm... as described in the commit log, this would be a bug when 
PAGE_SIZE is much smaller than IOMMU Page Size. This configuration doesn't
happen on current platform. So I didn't see this failure yet.

>
>Which commit introduced the breakage?

Hmm...  maybe we could say it is 'commit d084775738b7
<powerpc/iommu: Update the generic code to use dynamic iommu page sizes>'.
>>From this commit, powerpc iommu supports dynamic iommu page size. 

Before this commit, the size is aligned with PAGE_SIZE, so the value after
shift would be non-zero. After this commit, when PAGE_SIZE is smaller than
the IOMMU Page Size, shift right will make the size 0.

>
>cheers
>

-- 
Richard Yang
Help you, Help me