On Wednesday 18 November 2015 16:41:35 Peter Ujfalusi wrote:
On 11/18/2015 04:29 PM, Arnd Bergmann wrote:
On Wednesday 18 November 2015 16:21:26 Peter Ujfalusi wrote:
- non slave channel requests, where only the functionality matters, like
memcpy, interleaved, memset, etc. We could have a simple: dma_request_channel(mask);
But looking at the drivers using dmaengine legacy dma_request_channel() API: Some sets DMA_INTERRUPT or DMA_PRIVATE or DMA_SG along with DMA_SLAVE: drivers/misc/carma/carma-fpga.c DMA_INTERRUPT|DMA_SLAVE|DMA_SG drivers/misc/carma/carma-fpga-program.c DMA_MEMCPY|DMA_SLAVE|DMA_SG drivers/media/platform/soc_camera/mx3_camera.c DMA_SLAVE|DMA_PRIVATE sound/soc/intel/common/sst-firmware.c DMA_SLAVE|DMA_MEMCPY
as examples. Not sure how valid are these...
I just had a look myself. carma has been removed fortunately in linux-next, so we don't have to worry about that any more.
I assume that the sst-firmware.c case is a mistake, it should just use a plain DMA_SLAVE and not DMA_MEMCPY.
Aside from these, everyone else uses either DMA_CYCLIC in addition to DMA_SLAVE, which seems valid, or they use DMA_PRIVATE, which I think is redundant in slave drivers and can be removed.
It's usually not much harder to separate out the legacy case from the normal dma_request_slave_channel_reason(), so those drivers don't really need to use the unified compat API.
The current dma_request_slave_channel()/_reason() is not the 'legacy' API. Currently there is no way to get the reason why the dma channel request fails when using the _compat() version of the API, which is used by drivers which can be used in DT or in legacy mode as well. Sure, they all could have local if(){}else{} for handling this, but it is not a nice thing.
As it was discussed instead of adding the _reason() version for the _compat call, we should simplify the dmaengine API for getting the channel and at the same time we will have ERR_PTR returned instead of NULL.
What I meant was that we don't need to handle them with the unified simple interface. The users of DMA_CYCLIC can just keep using an internal helper that only deals with the legacy case, or use dma_request_slave() or whatever is the new API for the DT case.
Arnd