On 11/18/2015 04:29 PM, Arnd Bergmann wrote:

On Wednesday 18 November 2015 16:21:26 Peter Ujfalusi wrote:

quoted

2. 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...

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.

-- 
Péter
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