[alsa-devel] [PATCH 19/19] ASoC: fsi: Add DMAEngine support

Mark Brown broonie at opensource.wolfsonmicro.com
Fri Feb 3 15:14:40 CET 2012

On Fri, Feb 03, 2012 at 03:05:12PM +0100, Lars-Peter Clausen wrote:

> Yes, I was faced with the task of writing yet another dmaengine based ASoC
> PCM driver last week. At first I thought it might be a good idea to come up
> with a common ASoC PCM driver which could be used by all platforms using DMA
> engine. Unfortunately this turned out to be not feasible due to how
> dmaengine works. Each dmaengine driver has it's custom API for configuring
> the DMA controller. :/

That doesn't sound insurmountible - you need a callback to allow the
individual drivers to set the parameters but hopefully the data flow is
more generic?  There will probably be some other setup type stuff that
needs doing.

> The other ASoC platforms using dmaengine for their PCM driver (including the
> one in this patch series) don't have this function implemented and so the
> PCM drivers manually have to setup the cyclic SG lists. So while we could
> add a common set up functions for this to ASoC or ALSA I think the better
> place for this is in the dmaengine framework and implement
> device_prep_dma_cyclic for those drivers which don't do yet.

That seems like a good plan, that way other users of cyclic DMA will
also benefit.
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