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authorDan Williams <dan.j.williams@intel.com>2009-01-05 19:14:31 -0500
committerDan Williams <dan.j.williams@intel.com>2009-01-05 20:10:19 -0500
commit28405d8d9ce05f5bd869ef8b48da5086f9527d73 (patch)
treef3e68349cc38b4dc0a437455ba9513be78f620ae /Documentation/dmaengine.txt
parentfe0bdec68b77020281dc814805edfe594ae89e0f (diff)
async_tx, dmaengine: document channel allocation and api rework
"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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See Documentation/crypto/async-tx-api.txt