linux-kernel - Re: [PATCH v2 03/14] dma: edma: Add support for DMA

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Message-ID: <534855DF.2040309@ti.com>
Date:	Fri, 11 Apr 2014 15:51:43 -0500
From:	Joel Fernandes <joelf@...com>
To:	Vinod Koul <vinod.koul@...el.com>,
	Peter Ujfalusi <peter.ujfalusi@...com>
CC:	<dan.j.williams@...el.com>, <nsekhar@...com>,
	<dmaengine@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-omap@...r.kernel.org>,
	<davinci-linux-open-source@...ux.davincidsp.com>,
	<mporter@...aro.org>
Subject: Re: [PATCH v2 03/14] dma: edma: Add support for DMA_PAUSE/RESUME
 operation

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@...com>
>> ---
>>  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
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