[alsa-devel] [PATCH 1/2] ASoC: Add driver for PROTO Audio CODEC (with a WM8731)

[Codrin Ciubotariu]

On 29.08.2018 17:53, Mark Brown wrote:
> On Wed, Aug 29, 2018 at 05:47:26PM +0300, Codrin Ciubotariu wrote:
> 
>> +static const unsigned int wm8731_rates_12288000[] = {
>> +	8000, 32000, 48000, 96000,
>> +};
>> +
>> +static struct snd_pcm_hw_constraint_list wm8731_constraints_12288000 = {
>> +	.list = wm8731_rates_12288000,
>> +	.count = ARRAY_SIZE(wm8731_rates_12288000),
>> +};
>> +
>> +static int snd_proto_startup(struct snd_pcm_substream *substream)
>> +{
>> +	/* Setup constraints, because there is a 12.288 MHz XTAL on the board */
>> +	snd_pcm_hw_constraint_list(substream->runtime, 0,
>> +				   SNDRV_PCM_HW_PARAM_RATE,
>> +				   &wm8731_constraints_12288000);
>> +	return 0;
>> +}
> 
> This bit is better added to the CODEC driver since it'll apply to any
> system where there's this clock rate (someone else could come in and add
> other rates, no need to do that yourself though it'd be nice of course).

I could do it.

> 
> That also has the nice bonus that with that I think you'd be able to use
> the graph card rather than a custom driver?

The main reason for adding a custom driver and not using graph/simple 
card is the snd_soc_dai_set_sysclk(codec_dai, WM8731_SYSCLK_XTAL, 
                              XTAL_RATE, SND_SOC_CLOCK_IN) call. This 
enables the oscillator found in the wm8731 codec. Since 
WM8731_SYSCLK_XTAL is not 0, we can't use system-clock-frequency DT 
property to set it.

Best regards,
Codrin