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

[Ryan Lee <RyanS.Lee@maximintegrated.com>]

>-----Original Message-----
>From: Grant Grundler <grundler@chromium.org>
>Sent: Monday, November 26, 2018 6:28 PM
>To: Grant Grundler <grundler@chromium.org>
>Cc: Ryan Lee <RyanS.Lee@maximintegrated.com>; Liam Girdwood
><lgirdwood@gmail.com>; broonie@kernel.org; perex@perex.cz;
>tiwai@suse.com; Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>;
>Benson Leung <bleung@chromium.org>; alsa-devel@alsa-project.org; LKML
><linux-kernel@vger.kernel.org>
>Subject: Re: [PATCH] ASoC: max98373: Added max98373_reset for stable amp
>reset
>
>EXTERNAL EMAIL
>
>
>
>I just realized I had one more question...
>
>On Mon, Nov 26, 2018 at 6:24 PM Grant Grundler <grundler@chromium.org>
>wrote:
>>
>> 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@maximintegrated.com> wrote:
>> >
>> > Signed-off-by: Ryan Lee <ryans.lee@maximintegrated.com>
>> > ---
>> >  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.
>
>Why not poll the RevID register a few times until it gives a value?
>
>Then structure the code to try reset twice (maybe three times).
>This would avoid the unusual "sleep time after reset is increased" code.
Let me fix unusual things here. Thanks for the comment.

>
>cheers,
>grant
>
>> >            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