On Fri, Mar 8, 2019 at 10:59 PM Nicolin Chen <nicoleotsuka@xxxxxxxxx> 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. _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx https://mailman.alsa-project.org/mailman/listinfo/alsa-devel
