linux-kernel - Re: [PATCH 2/2] drivers/nvme: default to the IOMMU page size on Power

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Message-ID: <20151002173947.GA40695@linux.vnet.ibm.com>
Date:	Fri, 2 Oct 2015 10:39:47 -0700
From:	Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Matthew Wilcox <willy@...ux.intel.com>,
	Alexey Kardashevskiy <aik@...abs.ru>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
	Keith Busch <keith.busch@...el.com>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	linuxppc-dev@...ts.ozlabs.org,
	David Gibson <david@...son.dropbear.id.au>
Subject: Re: [PATCH 2/2] drivers/nvme: default to the IOMMU page size on Power

On 02.10.2015 [10:25:44 -0700], Christoph Hellwig wrote:
> Hi Nishanth,
> 
> please expose this value through the generic DMA API instead of adding
> architecture specific hacks to drivers.

Ok, I'm happy to do that instead -- what I struggled with is that I
don't have enough knowledge of the various architectures to provide the
right default implementation. It should be sufficient for the default to
return PAGE_SHIFT, and on Power just override that to return the IOMMU
table's page size? Since the only user will be the NVMe driver
currently, that should be fine?

Sorry for the less-than-ideal patch!

-Nish

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