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

[Doug Anderson <dianders@chromium.org>]

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.


> +       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?


> +                       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. I presume that your prepare() function isn't reentrant and
can't be called at the same time as your shutdown (right?).

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