[alsa-devel] [PATCH v4 2/2] soundwire: qcom: add support for SoundWire controller

[Srinivas Kandagatla]

On 01/11/2019 16:39, Pierre-Louis Bossart wrote:
> 
>>>> +static int qcom_swrm_prepare(struct snd_pcm_substream *substream,
>>>> +                 struct snd_soc_dai *dai)
>>>> +{
>>>> +    struct qcom_swrm_ctrl *ctrl = dev_get_drvdata(dai->dev);
>>>> +
>>>> +    if (!ctrl->sruntime[dai->id])
>>>> +        return -EINVAL;
>>>> +
>>>> +    return sdw_enable_stream(ctrl->sruntime[dai->id]);
>>>
>>> So in hw_params you call sdw_prepare_stream() and in _prepare you 
>>> call sdw_enable_stream()?
>>>
>>> Shouldn't this be handled in a .trigger operation as per the 
>>> documentation "From ASoC DPCM framework, this stream state is linked to
>>> .trigger() start operation."
>>
>> If I move sdw_enable/disable_stream() to trigger I get a big click 
>> noise on my speakers at start and end of every playback. Tried 
>> different things but nothing helped so far!. Enabling Speaker DACs 
>> only after SoundWire ports are enabled is working for me!
>> There is nothing complicated on WSA881x codec side all the DACs are 
>> enabled/disabled as part of DAPM.
> 
> that looks like a work-around to me? If you do a bank switch without 
> anything triggered, you are most likely sending a bunch of zeroes to 
> your amplifier and enabling click/pop removals somehow.
> 
> It'd be worth looking into this, maybe there's a missing digital 
> mute/unmute that's not done in the right order?

Digital mute does not help too, as they get unmuted before 
sdw_enable_stream() call in trigger, I hit same click sound.

Same in the disable path too!

Also I noticed that there are more than 20+ register read/writes in the 
sdw_enable_stream() path which took atleast 30 to 40 milliseconds.


I will try my luck checking the docs to see if I can find something 
which talks about this.

--srini


> 
>>
>>>
>>> It's also my understanding that .prepare will be called multiples times, 
>>
>> I agree, need to add some extra checks in the prepare to deal with this!
>>
>>> including for underflows and resume if you don't support INFO_RESUME.
>>
>>>
>>> the sdw_disable_stream() is in .hw_free, which is not necessarily 
>>> called by the core, so you may have a risk of not being able to recover?
>>
>> Hmm, I thought hw_free is always called to release resources allocated 
>> in hw_params.
>>
>> In what cases does the core not call this?
> 
> yes, but prepare can be called without hw_free called first. that's why 
> we updated the state machine to allow for DISABLED|DEPREPARED -> 
> PREPARED transitions.
> 
>>>> +static const struct dev_pm_ops qcom_swrm_dev_pm_ops = {
>>>> +    SET_RUNTIME_PM_OPS(qcom_swrm_runtime_suspend,
>>>> +               qcom_swrm_runtime_resume,
>>>> +               NULL
>>>> +    )
>>>> +};
>>>
>>> Maybe define pm_runtime at a later time then? We've had a lot of race 
>>> conditions to deal with, and it's odd that you don't support plain 
>>> vanilla suspend first?
>>>
>> Trying to keep things simple for the first patchset! added this 
>> dummies to keep the soundwire core happy!
> 
> If you are referring to the errors when pm_runtime is not enabled, we 
> fixed this is the series that's been out for review for 10 days now...
> 
> see '[PATCH 03/18] soundwire: bus: add PM/no-PM versions of read/write 
> functions', that should remove the need for dummy functions.
>