Messages in this thread | | | Date | Wed, 22 Dec 2010 23:54:03 +0000 | From | Russell King - ARM Linux <> | Subject | Re: [PATCH 06/13] DMAENGINE: driver for the ARM PL080/PL081 PrimeCells |
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On Wed, Dec 22, 2010 at 03:45:39PM -0800, Dan Williams wrote: > This is listed in the dmaengine documentation [1], but I obviously > missed this before merging. This also would have been caught by > lockdep as required by SubmitChecklist. As far as corrective action > before 2.6.37-final. It looks like this driver needs a full scrub > which seems unreasonable to complete and test over the holidays before > .37 lands. Linus we either need to mark this "depends on BROKEN" or > revert it. > > Support for the DMA_COMPL flags are necessary if the DMA_MEMCPY > capability is advertised, yes this driver got this wrong. I'll update > the documentation to make this requirement clear, and audit the other > drivers. With slave-only drivers the only usage model is one where > the client driver owns dma-mapping. In the non-slave (opportunistic > memcpy offload) case the client is unaware of the engine so the driver > owns unmapping. The minimal fix is to disable memcpy offload. > > -- > Dan > > [1] > 3.6 Constraints: > 1/ Calls to async_<operation> are not permitted in IRQ context. Other > contexts are permitted provided constraint #2 is not violated. > 2/ Completion callback routines cannot submit new operations. This > results in recursion in the synchronous case and spin_locks being > acquired twice in the asynchronous case.
(2) seems to be more than a little annoying - it seems that DMA engine drivers use a tasklet for running their DMA cleanup, which calls drivers callbacks, and we're going to have to have a whole pile of taskets in drivers just to be triggered from the completion callback. I can see this adding an additional layer of complexity and a nice fine set of shiney new races to deal with.
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