Re: [alsa-devel] [PATCH RFC (do not merge)] ASoC: davinci-mcasp: Set rule constraint if implicit bclk divider is used

On 03/13/2015 12:36 PM, Jyri Sarha wrote: [...]

In theory this patch does exactly what it is supposed to. It only allows a sample-rate and sample-format combination if the rate can be produced with reasonable accuracy. Unfortunately the alsa-lib and alsa-tools are not able use this information too well. If the requested sample-rate and sample-format is not available the aplay/arecord fails, even if plughw is selected, with:

pcm_params.c:170: snd1_pcm_hw_param_get_min: Assertion `!snd_interval_empty(i)' failed.

[...]

• /*

• * If we rely on implicit BCLK divider setting we should
  

• * set constraints based on what we can provide.
  

• */
  

• if (mcasp->bclk_master && mcasp->bclk_div == 0 && mcasp->sysclk_freq)

• return snd_pcm_hw_rule_add(substream->runtime, 0,
  

• 			   SNDRV_PCM_HW_PARAM_RATE,
  

• 			   davinci_mcasp_hw_rule_rate,
  

• 			   mcasp,
  

• 			   SNDRV_PCM_HW_PARAM_FRAME_BITS,
  

• 			   SNDRV_PCM_HW_PARAM_CHANNELS, -1);
  

For things to work correctly you also need reverse rules restricting CHANNELS and FRAME_BITS based on the RATE. This might fix the issue you are seeing with the ALSA tools.

- Lars