On 28.10.2015 [09:57:48 +1100], Julian Calaby wrote:

Hi Nishanth,

On Wed, Oct 28, 2015 at 9:20 AM, Nishanth Aravamudan
[off-list ref] wrote:

quoted

On 26.10.2015 [18:27:46 -0700], David Miller wrote:

quoted

From: Nishanth Aravamudan <redacted>
Date: Fri, 23 Oct 2015 13:54:20 -0700

quoted

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.

Ah, I see! Well, I don't know much about the DMA internals of most
architectures -- and my approach kept things functionally the same
everywhere (using PAGE_SHIFT) except:

a) Power, where I know it doesn't work as-is
and
b) sparc, where the code implied that a different value than PAGE_SHIFT
should be used.

Thanks,
Nish