Re: [PATCH] ASoC: max98373: Added max98373_reset for stable amp reset

[Grant Grundler]

Hi Ryan!

Just some questions inline - in general I like the reset function.

On Mon, Nov 26, 2018 at 10:46 AM Ryan Lee <RyanS.Lee@xxxxxxxxxxxxxxxxxxx> wrote:
>
> Signed-off-by: Ryan Lee <ryans.lee@xxxxxxxxxxxxxxxxxxx>
> ---
>  Changes : Created max98373_reset function to minimize code duplication.
>            Changed regmap_write to regmap_update_bits. Other bits except LSB need to be masked.
>            Added reset verification step to make sure software reset is completed well. Software reset is done in 10ms in normal case.
>            Revision ID is available when the amp is in the idle state which means software reset is completed.
>            Software reset will be performed maximum 3 times to avoid amp reset failure. Generally it is done in the first trial.
>            sleep time after software reset is increased + 30ms for every retrial. Maximum possible msleep time is 100 ms (initial 10 ms + 30 ms * 3 times).

Why is the sleep time increased after each SW reset?
What is the failure case that you've seen which would benefit from this?

>
>  sound/soc/codecs/max98373.c | 41 +++++++++++++++++++++++++++++++++++------
>  1 file changed, 35 insertions(+), 6 deletions(-)
>
> diff --git a/sound/soc/codecs/max98373.c b/sound/soc/codecs/max98373.c
> index a09d013..55af7f02 100644
> --- a/sound/soc/codecs/max98373.c
> +++ b/sound/soc/codecs/max98373.c
> @@ -724,14 +724,45 @@ static struct snd_soc_dai_driver max98373_dai[] = {
>         }
>  };
>
> +static void max98373_reset(struct max98373_priv *max98373, struct device *dev)
> +{
> +       int ret, reg, count, delay;
> +
> +       count = 0;
> +       while (true) {
> +               /* Software Reset */
> +               ret = regmap_update_bits(max98373->regmap,
> +                       MAX98373_R2000_SW_RESET,
> +                       MAX98373_SOFT_RESET,
> +                       MAX98373_SOFT_RESET);
> +               if (ret)
> +                       dev_err(dev, "Reset command failed. (ret:%d)\n", ret);
> +
> +               delay = 10000 + (count * 30000);
> +               usleep_range(delay, delay + 1000);
> +
> +               /* Software Reset Verification */
> +               ret = regmap_read(max98373->regmap,
> +                       MAX98373_R21FF_REV_ID, &reg);
> +               if (!ret) {
> +                       dev_info(dev, "Reset completed (retry:%d)\n", count);
> +                       break;

Instead of break, can the code return here?
"break" implies something else will happen after the while loop exits
- there isn't.

> +               }
> +
> +               if (++count > 3)        {
> +                       dev_err(dev, "Reset failed. (ret:%d)\n", ret);
> +                       break;
> +               }
> +               usleep_range(10000, 11000);

Why is there a second delay after reading MAX98373_R21FF_REV_ID?
Is this really necessary?

If the second usleep_range() isn't needed, it would be better/clearer
to make code loop on "while (count < 4)".   And then outside the while
loop, use dev_err() to share what the failure was.

> +       }
> +}
> +
>  static int max98373_probe(struct snd_soc_component *component)
>  {
>         struct max98373_priv *max98373 = snd_soc_component_get_drvdata(component);
>
>         /* Software Reset */
> -       regmap_write(max98373->regmap,
> -               MAX98373_R2000_SW_RESET, MAX98373_SOFT_RESET);
> -       usleep_range(10000, 11000);
> +       max98373_reset(max98373, component->dev);
>
>         /* IV default slot configuration */
>         regmap_write(max98373->regmap,
> @@ -818,9 +849,7 @@ static int max98373_resume(struct device *dev)
>  {
>         struct max98373_priv *max98373 = dev_get_drvdata(dev);
>
> -       regmap_write(max98373->regmap,
> -               MAX98373_R2000_SW_RESET, MAX98373_SOFT_RESET);
> -       usleep_range(10000, 11000);
> +       max98373_reset(max98373, dev);
>         regcache_cache_only(max98373->regmap, false);
>         regcache_sync(max98373->regmap);
>         return 0;
> --
> 2.7.4
>

cheers,
grant