Re: [v5] ASoC: qcom: lpass-cpu: Fix pop noise during audio capture begin

[Judy Hsiao <judyhsiao@google.com>]

On Fri, Jun 4, 2021 at 6:41 AM Doug Anderson <dianders@chromium.org> wrote:

> Judy,
>
> On Thu, Jun 3, 2021 at 8:08 AM Judy Hsiao <judyhsiao@chromium.org> wrote:
> >
> > @@ -315,12 +353,54 @@ static int lpass_cpu_daiops_trigger(struct
> snd_pcm_substream *substream,
> >         return ret;
> >  }
> >
> > +static int lpass_cpu_daiops_prepare(struct snd_pcm_substream *substream,
> > +               struct snd_soc_dai *dai)
> > +{
> > +       struct lpass_data *drvdata = snd_soc_dai_get_drvdata(dai);
> > +       struct lpaif_i2sctl *i2sctl = drvdata->i2sctl;
> > +       unsigned int id = dai->driver->id;
> > +       int ret;
> > +       /*
> > +        * Ensure lpass BCLK/LRCLK is enabled bit before playback/capture
> > +        * data flow starts. This allows other codec to have some delay
> before
> > +        * the data flow.
> > +        * (ex: to drop start up pop noise before capture starts).
> > +        */
>
> nit: there's usually a blank line between the variable declarations
> and the first line of code, even if the first line of code is a
> comment.
> Thanks, noted.
>
> > +       if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
> > +               ret = regmap_fields_write(i2sctl->spken, id,
> LPAIF_I2SCTL_SPKEN_ENABLE);
> > +       else
> > +               ret = regmap_fields_write(i2sctl->micen, id,
> LPAIF_I2SCTL_MICEN_ENABLE);
> > +
> > +       if (ret) {
> > +               dev_err(dai->dev, "error writing to i2sctl reg: %d\n",
> ret);
> > +               return ret;
> > +       }
> > +
> > +       /*
> > +        * Check mi2s_was_prepared before enabling BCLK as
> lpass_cpu_daiops_prepare can
> > +        * be called multiple times. It's paired with the clk_disable in
> > +        * lpass_cpu_daiops_shutdown.
> > +        */
> > +       if (!drvdata->mi2s_was_prepared[dai->driver->id]) {
> > +               drvdata->mi2s_was_prepared[dai->driver->id] = true;
> > +               ret = clk_enable(drvdata->mi2s_bit_clk[id]);
> > +               if (ret) {
> > +                       dev_err(dai->dev, "error in enabling mi2s bit
> clk: %d\n", ret);
> > +                       clk_disable(drvdata->mi2s_osr_clk[id]);
>
> Can you explain why this clk_disable() is here? Your function didn't
> turn this clock on, so why should it be turning it off in the error
> case?
>
The OSR CLK is disabled in the error case, not the BCLK.

>
>
> > +                       drvdata->mi2s_was_prepared[dai->driver->id] =
> false;
> > +                       return ret;
> > +               }
>
> Why not put the `drvdata->mi2s_was_prepared[dai->driver->id] = true;`
> _after_ you check for errors. Then you don't need to undo it in the
> error case.

Noted, thanks.

> I presume that your prepare() function isn't reentrant and
> can't be called at the same time as your shutdown (right?).
>
https://elixir.bootlin.com/linux/latest/source/sound/soc/soc-pcm.c#L658
https://elixir.bootlin.com/linux/latest/source/sound/soc/soc-pcm.c#L825
I think yes,
snd_soc_pcm_dai_prepare and snd_soc_dai_shutdown are both guard by
mutex_lock_nested(&rtd->card->pcm_mutex, rtd->card->pcm_subclass);

>
> Other than that, I don't have any objections to this patch anymore. I
> probably won't add a formal "Reviewed-by", though, since I _really_
> don't know anything about the issue at hand or the code. I just
> stumbled upon this because I was getting the clock splat at bootup. If
> someone feels like this needs me to spin up enough to understand /
> really review this patch then please yell.
>
> -Doug
>