dw-dma: use done bit for linked list transfers

[tlauda]

Changes settings of GPDMA linked lists transfers
to use done bit to let the DMA know, that the next
data block is ready to be sent/received. This way
we are sure, that there will be no additional data
transferred between receiving interrupt and disabling
GPDMA channel.

Signed-off-by: Tomasz Lauda tomasz.lauda@linux.intel.com

[RanderWang]

I test it on BDW and it is ok

[RanderWang]

@tlauda @lgirdwood @keyonjie

Hi tomasz, I have a question about this change. Is this patch for pause-release case?

My understanding is that: DMA engine would be halted and wait for DONE bit cleared in IRQ
function then go on copying data to SSP. Before DONE bit is cleared, no data is copied to SSP,
but SSP is still sending data to codec. So SSP is halted or sending some invalidate data to codec.

This would do negative effect to sound quality. And I think pause-release is a corner case for enjoying
music, it is not worth doing so.

[tlauda]

@RanderWang It's the other way around. DMA transfers the first linked list item and waits for DONE to transfer the next one. If we are going to press pause, then we are stopping both DMA and SSP in the middle of the transfer, so there won't be any problems with invalid data. The only potential issue I can see is data inconsistency after pause/release. There is a high probability, that the part of the linked list item data will be lost, because after release we are going to start from the next lli, but I will try to deal with it later.

[RanderWang]

@tlauda yes, I get your idea. Actually, I don't care about pause-release case. I just want to know whether it affect normal case, just playback.