Re: [PATCH 02/13] dmaengine: Introduce dma_request_slave_channel_compat_reason()

From: Peter Ujfalusi
Date: Wed Nov 18 2015 - 09:42:03 EST

On 11/18/2015 04:29 PM, Arnd Bergmann wrote:
> On Wednesday 18 November 2015 16:21:26 Peter Ujfalusi wrote:
>> 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.

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