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

[Lars-Peter Clausen]

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