Re: [PATCH v2 03/14] dma: edma: Add support for DMA_PAUSE/RESUME operation

[Joel Fernandes <joelf-l0cyMroinI0@public.gmane.org>]

On 04/11/2014 11:43 AM, Vinod Koul wrote:
> On Tue, Apr 01, 2014 at 04:06:04PM +0300, Peter Ujfalusi wrote:
>> Pause/Resume can be used by the audio stack when the stream is paused/resumed
>> The edma platform code has support for this and the legacy audio stack used
>> this.
>>
>> Signed-off-by: Peter Ujfalusi <peter.ujfalusi-l0cyMroinI0@public.gmane.org>
>> ---
>>  drivers/dma/edma.c | 28 ++++++++++++++++++++++++++++
>>  1 file changed, 28 insertions(+)
>>
>> diff --git a/drivers/dma/edma.c b/drivers/dma/edma.c
>> index 2742867fd1e6..7891378a03f0 100644
>> --- a/drivers/dma/edma.c
>> +++ b/drivers/dma/edma.c
>> @@ -240,6 +240,26 @@ static int edma_slave_config(struct edma_chan *echan,
>>  	return 0;
>>  }
>>  
>> +static int edma_dma_pause(struct edma_chan *echan)
>> +{
>> +	/* Pause/Resume only allowed with cyclic mode */
>> +	if (!echan->edesc->cyclic)
>> +		return -EINVAL;
> why this artificial restriction? The driver can do pause even for non cyclic
> cases too? Yes the usage is in cyclic context but why should we limit any future
> work on this?
> 

We struggled with this, and we certainly we don't want pauses in
non-cyclic EDMA... we tried doing a "pause" and it was a disaster as the
events keep coming in and those can't be paused, and EDMA hardware wont
queue them during the pause, it'll just generate an error interrupt storm.

Thanks,
-Joel