5 Aug
2014
5 Aug
'14
6:56 p.m.
On Mon, Aug 04, 2014 at 06:50:17PM +0200, Laurent Pinchart wrote:
The question was why is there a dma_async_issue_pending() operation at all ? Why can't dmaengine_submit() triggers the transfer start ? The only explanation is a small comment in dmaengine.h that states
- This allows drivers to push copies to HW in batches,
- reducing MMIO writes where possible.
I don't think that's applicable for DMA slave transfers. Is it still applicable for anything else ?
why not?
If your hw supports sg-lists and say length of 8 and you prepare two descriptors for lengths of 3 and 5. While in issue pending what prevents you from submiiting them in one shot to hardware while still getting interrupt.
I know designware and intel-dma do support that. It is different point that drivers don't
--
~Vinod