[RFC] dmaengine: omap-dma: Allow DMA controller to prefetch data

[Russell King - ARM Linux]

On Thu, Oct 18, 2012 at 03:20:46PM -0700, Mark A. Greer wrote:
> This patch seems fairly stable but I've only tested omap-sham (crypto)
> and omap_hsmmc (mmc) on an am37x EVM.  I also enabled burst mode but
> that made the system unstable when exercising either omap-sham or
> omap_hsmmc.  I'm unaware of any errata that would make this an unwanted
> modification but I haven't checked all of the SoCs.  Are there other
> reasons that this should be applied??

It definitely needs checking with audio, because it will affect the
pointer position in relation to audio output, and it will have an
effect on how much audio data is lost over a pause/resume event.

Unfortunately, the OMAP DMA hardware has no way to do a proper "pause",
it can only do a "stop" which involves dumping its FIFOs on the floor
in the case of anything but a DEV->MEM transfer.  So the more data
held in the DMA hardware, the more is lost on pause.