Improve the documentation for the slave and cyclic DMA engine support
reformatting it for easier reading, adding further APIs, splitting it
into five steps, and including references to the documentation in
dmaengine.h.
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>
[Fixed the index title to reflect new changes]
Signed-off-by: NVinod Koul <vinod.koul@intel.com>

Signed-off-by: NVinod Koul <vinod.koul@intel.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

"Wouldn't it be better if the dmaengine layer made sure it didn't pass
the same channel several times to a client?

I mean, you seem concerned that the memcpy() API should be transparent
and easy to use, but the whole registration interface is just
ridiculously complicated..."
	- Haavard

The dmaengine and async_tx registration/allocation interface is indeed
needlessly complicated.  This redesign has the following goals:

1/ Simplify reference counting: dma channels are not something one would
   expect to be hotplugged, it should be an exceptional event handled by
   drivers not something clients should be mandated to handle in a
   callback.  The common case channel removal event is 'rmmod <dma driver>',
   which for simplicity should be disallowed if the channel is in use.
2/ Add an interface for requesting exclusive access to a channel
   suitable to device-to-memory users.
3/ Convert all memory-to-memory users over to a common allocator, the goal
   here is to not have competing channel allocation schemes.  The only
   competition should be between device-to-memory exclusive allocations and
   the memory-to-memory usage case where channels are shared between
   multiple "clients".

Cc: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>
Cc: Neil Brown <neilb@suse.de>
Cc: Jeff Garzik <jeff@garzik.org>
Reviewed-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>