[alsa-devel] [PATCH] ASoC: nau8825: erase pop noise by soft mute

[John Hsu]

On 10/3/2016 7:21 PM, John Hsu wrote:
> On 9/25/2016 3:11 AM, Mark Brown wrote:
>> On Wed, Sep 14, 2016 at 03:47:32PM +0800, John Hsu wrote:
>>
>>  
>>> + * Enable soft mute to gradually lower DAC volume to zero;
>>> + * Soft unmute will gradually increase DAC volume to volume setting.
>>>     
>>
>>  
>>> +        regmap_write(nau8825->regmap, NAU8825_REG_DAC_DGAIN_CTRL, 0);
>>> +        regmap_update_bits(nau8825->regmap, NAU8825_REG_MUTE_CTRL,
>>> +            NAU8825_DAC_SOFT_MUTE, NAU8825_DAC_SOFT_MUTE);
>>>     
>>
>> Why are we not just exposing soft mute as a userspace control like other
>> drivers do?  It seems like there's some weird interaction between
>> sidetones and the soft mute which this is trying to work around but
>> that's not really explained, it seems to be the main point here.
>> Basically I can't figure out what's intended here.
>>
>>   
>
> The issue only happens in the begin of playback. The amplitude of
> output signal has abnormal change in a short time and then recover
> to the level by user configuration. The amplitude change makes pop
> noise. For the reason, we use soft mute to fix the pop noise because
> the signal will output from small to normal case gradually. But the
> steps of soft mute is not enough to cover the period of amplitude
> change. Thus, we need to defer the soft mute and put the triggered
> point near the signal output. The userspace control can't catch the
> point as we wish.
>
>>> +EXPORT_SYMBOL_GPL(nau8825_soft_mute);
>>>     
>>
>> Why is this exported, how will it be used?  The function seems to be
>> called from inside this driver as well...
>>   
>
> The function is exported for the machine driver. When the platform
> stops the playback and it makes soft mute. When the playback starts,
> the playform makes soft unmute in trigger start function. The trigger
> function is the closest point of output signal, and the codec driver
> can make the soft unmute deferring as short as possible.
>
>

We want to abandon the patch under reviewing because there is another
study and solution for the pop noise. What should I do to abandon the
patch? Thank you for the advice.