Subject: [PATCH v2 2/6] ASoC: dwc: Ensure FIFOs are flushed to prevent channel swap

From: [email-masked] (Andrew Jackson)
Date: Mon, 15 Dec 2014 08:37:52 +0000

On 12/12/14 09:37, Lars-Peter Clausen wrote:
> On 12/12/2014 10:25 AM, Andrew Jackson wrote:
>> From: Andrew Jackson <[email-masked]>
>>
>> If the FIFOs aren't flushed, the left/right channels may be swapped:
>> this may occur if the FIFOs are not empty when the streams start.
>>
>> Signed-off-by: Andrew Jackson <[email-masked]>
>> ---
>>   sound/soc/dwc/designware_i2s.c |    2 ++
>>   1 files changed, 2 insertions(+), 0 deletions(-)
>>
>> diff --git a/sound/soc/dwc/designware_i2s.c b/sound/soc/dwc/designware_i2s.c
>> index ef771ea..b9d6a25 100644
>> --- a/sound/soc/dwc/designware_i2s.c
>> +++ b/sound/soc/dwc/designware_i2s.c
>> @@ -228,12 +228,14 @@ static int dw_i2s_hw_params(struct snd_pcm_substream *substream,
>>   	i2s_disable_channels(dev, substream->stream);
>>
>>   	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {
>> +		i2s_write_reg(dev->i2s_base, TXFFR, 1);
>>   		i2s_write_reg(dev->i2s_base, TCR(ch_reg), xfer_resolution);
>>   		i2s_write_reg(dev->i2s_base, TFCR(ch_reg), 0x02);
>>   		irq = i2s_read_reg(dev->i2s_base, IMR(ch_reg));
>>   		i2s_write_reg(dev->i2s_base, IMR(ch_reg), irq & ~0x30);
>>   		i2s_write_reg(dev->i2s_base, TER(ch_reg), 1);
>>   	} else {
>> +		i2s_write_reg(dev->i2s_base, RXFFR, 1);
>>   		i2s_write_reg(dev->i2s_base, RCR(ch_reg), xfer_resolution);
>>   		i2s_write_reg(dev->i2s_base, RFCR(ch_reg), 0x07);
>>   		irq = i2s_read_reg(dev->i2s_base, IMR(ch_reg));
>>
> 
> This should probably go into the prepare callback. prepare is for example 
> also called when recovering from a underrun/overrun. Whereas hwparams is 
> only called during initial setup of the stream.

That's a good idea: thank you.  I'll rework the patch with this in mind.

	Andrew