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 for <linuxppc-dev@lists.ozlabs.org>; Sat,  3 Oct 2015 18:20:11 +1000 (AEST)
Date: Sat, 3 Oct 2015 01:19:52 -0700
From: Christoph Hellwig <hch@infradead.org>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Nishanth Aravamudan <nacc@linux.vnet.ibm.com>,
 Matthew Wilcox <willy@linux.intel.com>,
 Keith Busch <keith.busch@intel.com>, Paul Mackerras <paulus@samba.org>,
 Michael Ellerman <mpe@ellerman.id.au>,
 Alexey Kardashevskiy <aik@ozlabs.ru>,
 David Gibson <david@gibson.dropbear.id.au>,
 Christoph Hellwig <hch@infradead.org>,
 linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org,
 linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH 0/5 v2] Fix NVMe driver support on Power with 32-bit DMA
Message-ID: <20151003081952.GC24025@infradead.org>
References: <20151002171606.GA41011@linux.vnet.ibm.com>
 <20151002200953.GB40695@linux.vnet.ibm.com>
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On Sat, Oct 03, 2015 at 06:51:06AM +1000, Benjamin Herrenschmidt wrote:
> On Fri, 2015-10-02 at 13:09 -0700, Nishanth Aravamudan wrote:
> 
> > 1) add a generic dma_get_page_shift implementation that just returns
> > PAGE_SHIFT
> 
> So you chose to return the granularity of the iommu to the driver
> rather than providing a way for the driver to request a specific
> alignment for DMA mappings. Any specific reason ?

At least for NVMe that's the way to go - it allows to set a page set in
the device which should fit the IOMMU page size.