linux-kernel - Re: [PATCH 0/5 v3] Fix NVMe driver support on Power with 32-bit DMA

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Message-ID: <CAGRGNgXV+RJvjOBe351HyguYkonQ8F=CM3uZTijcqoQg6ArAcw@mail.gmail.com>
Date:	Wed, 28 Oct 2015 09:57:48 +1100
From:	Julian Calaby <julian.calaby@...il.com>
To:	Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>
Cc:	David Miller <davem@...emloft.net>, willy@...ux.intel.com,
	keith.busch@...el.com, benh@...nel.crashing.org, paulus@...ba.org,
	mpe@...erman.id.au, aik@...abs.ru, david@...son.dropbear.id.au,
	Christoph Hellwig <hch@...radead.org>,
	linux-nvme@...ts.infradead.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linuxppc-dev@...ts.ozlabs.org,
	sparclinux <sparclinux@...r.kernel.org>
Subject: Re: [PATCH 0/5 v3] Fix NVMe driver support on Power with 32-bit DMA

Hi Nishanth,

On Wed, Oct 28, 2015 at 9:20 AM, Nishanth Aravamudan
<nacc@...ux.vnet.ibm.com> wrote:
> On 26.10.2015 [18:27:46 -0700], David Miller wrote:
>> From: Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>
>> Date: Fri, 23 Oct 2015 13:54:20 -0700
>>
>> > 1) add a generic dma_get_page_shift implementation that just returns
>> > PAGE_SHIFT
>>
>> I won't object to this patch series, but if I had implemented this I
>> would have required the architectures to implement this explicitly,
>> one-by-one.  I think it is less error prone and more likely to end
>> up with all the architectures setting this correctly.
>
> Well, looks like I should spin up a v4 anyways for the powerpc changes.
> So, to make sure I understand your point, should I make the generic
> dma_get_page_shift a compile-error kind of thing? It will only fail on
> architectures that actually build the NVME driver (as the only caller).
> But I'm not sure how exactly to achieve that, if you could give a bit
> more detail I'd appreciate it!

He's suggesting that you _don't_ put a generic implementation in
/include/linux/dma-mapping.h and instead add it to _every_
architecture.

Thanks,

-- 
Julian Calaby

Email: julian.calaby@...il.com
Profile: http://www.google.com/profiles/julian.calaby/
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