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

From: Peter Ujfalusi
Date: Wed Nov 18 2015 - 09:21:51 EST

Hi Vinod,

bringing this old thread back to life as I just started to work on this.

On 06/24/2015 07:24 PM, Vinod Koul wrote:

>> We would end up with the following APIs, all returning with error code on failure:
>> dma_request_slave_channel(dev, name);
>> dma_request_channel_legacy(mask, fn, fn_param);
>> dma_request_slave_channel_compat(mask, fn, fn_param, dev, name);
>> dma_request_any_channel(mask);
> This is good idea but still we end up with 4 APIs. Why not just converge to
> two API, one legacy + memcpy + filer fn and one untimate API for slave?

Looked at the current API and it's use and, well, it is a bit confusing.

What I hoped that we can separate users to two category:
1. Slave channel requests, where we request a specific channel to handle HW
For this we could have:
dma_request_slave_channel(dev, name, fn, fn_param);

In DT/ACPI only drivers we can NULL out the fn and fn_param, in pure legacy
mode we null out the name, I would keep the dev so we could print dev specific
error in dmaengine core, but it could be optional, IN case of drivers used
both DT/ACPI and legacy mode all parameter can be filled and the core will
decide what to do.
For the legacy needs the dmaengine code would provide the mask dows with
DMA_SLAVE flag set.

2. non slave channel requests, where only the functionality matters, like
memcpy, interleaved, memset, etc.
We could have a simple:

But looking at the drivers using dmaengine legacy dma_request_channel() API:
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...

Some drivers do pass fn and fn_param when requesting channel for DMA_MEMCPY
sound/soc/intel/common/sst-firmware.c (well, this request DMA_SLAVE capability
at the same time).

Some driver sets the fn_param w/o fn, which means fn_param is ignored.

So the
dma_request_slave_channel(dev, name, fn, fn_param);

almost covers the current users and would be pretty clean ;)

If we add the mask to the slave channel API - which will become universal,
drop in replacement for dma_request_channel, and we might have only one API:

dma_request_channel(dev, name, mask, fn, fn_param);

> Internally we may have 4 APIs for cleaner handling...
> Thoughts... ??

Yes, as we need to arrange the code internally to keep things neat.

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