Re: [alsa-devel] [PATCH 14/18] ASoC: davinci: Add edma dmaengine platform driver

[Lars-Peter Clausen]

On 03/13/2014 02:03 PM, Peter Ujfalusi wrote:
> On 03/13/2014 12:28 PM, Lars-Peter Clausen wrote:
> > > +int edma_pcm_platform_register(struct device *dev)
> > > +{
> > > +    if (dev->of_node)
> > > +        return snd_dmaengine_pcm_register(dev,
> > > +                    &edma_dmaengine_pcm_config,
> > > +                    SND_DMAENGINE_PCM_FLAG_NO_RESIDUE);
> >
> > Since the edma dmaengine driver implements the slave cap API there is no need
> > to manually specify SND_DMAENGINE_PCM_FLAG_NO_RESIDUE manually. But since the
> > edma driver sets the granularity to DMA_RESIDUE_GRANULARITY_DESCRIPTOR in this
> > case the generic dmaengine will not set SND_DMAENGINE_PCM_FLAG_NO_RESIDUE
> > automatically since it assumes that the dmaengine driver is capable of
> > properly reporting the DMA position.
>
> Hrm, I see. For eDMA I think we can support DMA_RESIDUE_GRANULARITY_SEGMENT
> granularity. Since according to the documentation the _SEGMENT means that the
> DMA position will be updated per periods, which is basically the same thing
> what we are doing at the moment when the granularity is
> DMA_RESIDUE_GRANULARITY_DESCRIPTOR.
>  From ALSA point of view at least they are the same: neither of them can report
> exact position, the DMA pointer jumps from period to period.
>
> IMHO in the generic dmaengine PCM we should set the SNDRV_PCM_INFO_BATCH for
> both cases.

Ups, sorry mixed up DMA_RESIDUE_GRANULARITY_SEGMENT and 
DMA_RESIDUE_GRANULARITY_DESCRIPTOR. You can just remove the 
SND_DMAENGINE_PCM_FLAG_NO_RESIDUE when registering the dmaengine PCM driver 
and everything will still work as expected.
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