On Fri, Mar 8, 2019 at 10:59 PM Nicolin Chen nicoleotsuka@gmail.com wrote:
On Fri, Mar 08, 2019 at 05:39:30PM +0000, Daniel Baluta wrote:
@@ -542,6 +544,11 @@ static int fsl_sai_trigger(struct snd_pcm_substream *substream, int cmd, case SNDRV_PCM_TRIGGER_START: case SNDRV_PCM_TRIGGER_RESUME: case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
for (i = 0; tx && i < channels; i++)regmap_write(sai->regmap, FSL_SAI_TDR, 0x0);Though it could reduce underrrun for sure, I don't feel it's a thorough fix, especially when dealing with a duplex case where RX is the first stream while the driver enables both TE and RE at the same time. So the transmitter might have started before TX DMA request gets enabled.
I see your point here. This is trickier than I expected.
We actually have something similar in the ESAI driver as that one is well documented. But SAI is apparently more tricky at the trigger() function. And the paragraph you pasted from the RM doesn't explicitly sound like we should do this.
Btw, Instead of writing dummy data, have you tried polling the WFP pointer of the TFR0 register to make sure data is copied by the DMA?
This is a good suggestion. Will give it a try.
if (tx)udelay(10);Any justification for the delay? Missing a line of comments? I guess it's to address the 3-bit clocks timing. However, putting it before enabling DMA request doesn't make much sense to me.
Indeed. Will come back with a better patch in v3.
thanks, Daniel.