DMAENGINE: Client reuse of desc

[Per Forlin]

Hi,

DMA_CTRL_ACK is used if the client needs to set up a dependency chain
of descriptor. This mean the driver cannot reuse or free the
descriptor until the client release it. I wonder if the client is
permitted/safe to reuse the descriptor and submit it again to the
driver? Or would dmaengine need an additional flag for this feature.

I know that the intent of DMA_CTRL_ACK is not to allow reuse of desc
from a client perspective. I am asking because I made this assumption
when implementing it in ste_dma40.

Example:
The client prepares a desc "A", submits "A" and starts the transfer.
When tx finished, the client then fills in new data in the desc
"A"-buffer and submits it again.

/Per
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