Re: [PATCH] CHROMIUM: ASoC: Intel: boards: Use FS as nau8825 sysclk in nau88l25_max98357a machine

[Charles Keepax <ckeepax@opensource.wolfsonmicro.com>]

On Fri, Nov 18, 2016 at 10:58:46AM +0530, Vinod Koul wrote:
> On Thu, Nov 17, 2016 at 02:35:15PM +0800, Grace Kao wrote:
> > 256FS sysclk gives the best audio quality per nau8825 datasheet.
> > 
> > Loud headphone pop happens if there is no sysclk during nau8825
> > playback power up sequence. Currently Skylake does not output MCLK/FS
> > when the back-end DAI op hw_param is called, so we cannot switch to
> > MCLK/FS in hw_param. This patch reduces pop by leting nau8825 keep
> > using its internal VCO clock during widget power up sequence, until
> > SNDRV_PCM_TRIGGER_START when MCLK/FS is available.
<snip>
> 
> > +static int skylake_nau8825_trigger(struct snd_pcm_substream *substream, int cmd)
> > +{
> > +	struct snd_soc_pcm_runtime *rtd = substream->private_data;
> > +	struct snd_pcm_runtime *runtime = substream->runtime;
> > +	struct snd_soc_dai *codec_dai = rtd->codec_dai;
> > +	int ret = 0;
> > +
> > +	switch (cmd) {
> > +	case SNDRV_PCM_TRIGGER_START:
> > +		ret = snd_soc_dai_set_sysclk(codec_dai,	NAU8825_CLK_FLL_FS, 0,
> > +			SND_SOC_CLOCK_IN);
> > +		if (ret < 0)
> > +			dev_err(codec_dai->dev, "can't set FS clock %d\n", ret);
> > +		ret = snd_soc_dai_set_pll(codec_dai, 0, 0, runtime->rate,
> > +			runtime->rate * 256);
> > +		if (ret < 0)
> > +			dev_err(codec_dai->dev, "can't set FLL: %d\n", ret);
> > +		break;
> 
> starting clock on trigger doesnt sound right to me..
> 

Me neither can't trigger be called from an atomic context? In
which case I would expect operations on an external CODEC to be
very likely to cause issues.

Thanks,
Charles