tree 588a08f0c2aeef6e4f615ce9db016b2bae4b85aa
parent fecdef932b0093b4a7e1ae88b1dbd63eb74ecc34
author Nandor Han <nandor.han@ge.com> 1470659905 +0300
committer Greg Kroah-Hartman <gregkh@linuxfoundation.org> 1472653648 +0200

dmaengine: imx-sdma - reduce transfer latency for DMA cyclic clients

Having the SDMA driver use a tasklet for running the clients
callback introduce some issues:
  - probability to have desynchronized data because of the
    race condition created since the DMA transaction status
    is retrieved only when the callback is executed, leaving
    plenty of time for transaction status to get altered.
  - inter-transfer latency which can leave channels idle.

Move the callback execution, for cyclic channels, to SDMA
interrupt (as advised in `Documentation/dmaengine/provider.txt`)
to (a)reduce the inter-transfer latency and (b) eliminate the
race condition possibility where DMA transaction status might
be changed by the time is read.

The responsibility of the SDMA interrupt latency
is moved to the SDMA clients which case by case should defer
the work to bottom-halves when needed.

Tested-by: Peter Senna Tschudin <peter.senna@collabora.com>
Acked-by: Peter Senna Tschudin <peter.senna@collabora.com>
Reviewed-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Nandor Han <nandor.han@ge.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>