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

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Date:	Sat, 03 Oct 2015 07:35:09 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>
Cc:	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 Fri, 2015-10-02 at 14:04 -0700, Nishanth Aravamudan wrote:
> Right, I did start with your advice and tried that approach, but it
> turned out I was wrong about the actual issue at the time. The problem
> for NVMe isn't actually the starting address alignment (which it can
> handle not being aligned to the device's page size). It doesn't handle
> (addr + len % dev_page_size != 0). That is, it's really a length
> alignment issue.
> 
> It seems incredibly device specific to have a an API into the DMA code
> to request an end alignment -- no other device seems to have this
> issue/design. If you think that's better, I can fiddle with that
> instead.
> 
> Sorry, I should have called this out better as an alternative
> consideration.

Nah it's fine. Ok. Also adding the alignment requirement to the API
would have been a much more complex patch since it would have had to
be implemented for all archs.

I think your current solution is fine.

Cheers,
Ben.

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