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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: Russell King <rmk+kernel@arm.linux.org.uk>
[Fixed the index title to reflect new changes]
Signed-off-by: Vinod Koul <vinod.koul@intel.com>
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Signed-off-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
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"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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
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