[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.