Lars-Peter Clausen <lars@xxxxxxxxxx> writes: > On 07/10/2015 01:40 PM, Jun Nie wrote: >>>> Furthermore audio DMA uses cyclic DMA, so it doesn't even hit this code >>>> path, so the patch description doesn't really add up to the changes. Actually I'd like to know _exactly_ which code is hit there, which dmaengine user. I have found that fsl_asrc_dma.c uses the flag "DMA_CTRL_ACK", without using anywhere the async_ack() method (I might be wrong, I don't know that code). The question behind is : which driver has a regression, for what purpose is it setting the DMA_CTRL_ACK bit ? That would help to know if I used a bit whose purpose what already well defined, or if it's just a driver which sets DMA_CTRL_ACK without really needing it. If we find that DMA_CTRL_ACK has a specific meaning, or a "dmaengine driver" specific meaning (ie. not usable by dmaengine clients), then another flag will probably be necessary. >>> Sorry, it does. Looked at the wrong line. Reverting b9855f03d560 is probably >>> the right thing to do as it breaks the existing semantics in a very bad way >>> causing descriptors to be not freed when they should be. >> I guess my change does not meet video requirement for patch >> b9855f03d560, but I do not know detail video usage case related to >> that patch. You can either revert the patch or confirm change in this >> email is OK for the video case. > To handle the video case something else is needed. The current dmaengine > semantics are that once a descriptor is passed to dma_engine_submit() it is > owned by the DMAengine driver and the client must never ever touch it > again. > Commit b9855f03d560 overloaded DMA_CTRL_ACK to mean that the should be > re-usable by the client. But this breaks existing users of DMA_CTRL_ACK since > its a completely new and different meaning to the existing one. For marking a > descriptor as reusable for the client a new flag should probably be > introduced. Maybe yes. The problem will be to list the existing users of DMA_CTRL_ACK (dmaengine slave API side), and see what is their expectation from this bit. >From the discussion we had with Vinod, there was no clear definition so far for DMA_CTRL_ACK (still for dmaengine slave API). I might have overlooked something here, so any input will be valuable. Cheers. -- Robert -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
