linux-kernel - Re: [PATCH 0/5 v2] Fix NVMe driver support on Power with 32-bit DMA

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Message-ID: <20151003081952.GC24025@infradead.org>
Date:	Sat, 3 Oct 2015 01:19:52 -0700
From:	Christoph Hellwig <hch@...radead.org>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>,
	Matthew Wilcox <willy@...ux.intel.com>,
	Keith Busch <keith.busch@...el.com>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Alexey Kardashevskiy <aik@...abs.ru>,
	David Gibson <david@...son.dropbear.id.au>,
	Christoph Hellwig <hch@...radead.org>,
	linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 0/5 v2] Fix NVMe driver support on Power with 32-bit DMA

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.
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