On 11/29/2013 02:08 PM, Arnd Bergmann wrote:

On Monday 25 November 2013, Stephen Warren wrote:

quoted

Well, you suggested not using of_dma_simple_xlate() since it wasn't
appropriate. I then started to implement an open-coded xlate function,
but found that it was 99% identical to the same thing in the mmp driver,
and hence created a common of_dma_slave_xlate() so as not to just
cut/paste it everywhere. Unfortunately, I only sent that patch to
dmaengine at vger.kernel.org and the DMA maintainers, and there's no
archive of that list:-(

Ok, I see. However, I think the need for nontrivial code to be duplicated
across drivers is not a sign that we are missing a generic xlate function
and another indirection level, but rather that we got the interface
for dma_get_slave_channel() wrong (yes, that would be my fault).

Can you try coming up with a different method to achieve the same
where you use a different helper from the driver specific xlate
function that does not require a callback?

I think dma_get_slave_channel is great if you have one channel per
request line and you can directly look up the channel from the
DT data, but it is not good if you have pick a channel and work
around the race.

Hmm. Can you take a look at "[PATCH V4] dma: add
dma_get_any_slave_channel(), for use in of_xlate()" at the link below.
It still implements this via xlate, but I don't see any benefit in
making drivers use a different API to request slave channels based on
how the DMA controller works.

http://lkml.org/lkml/2013/11/26/408