Functionality of pcm_notify in snd-aloop?

[Pavel Hofman]

Dne 30. 03. 20 v 17:09 Jaroslav Kysela napsal(a):
> Dne 30. 03. 20 v 16:43 Pavel Hofman napsal(a):
>>
>> Dne 26. 03. 20 v 18:59 Pavel Hofman napsal(a):
>>> Dne 26. 03. 20 v 18:44 Jaroslav Kysela napsal(a):
>>>> Dne 26. 03. 20 v 18:19 Pavel Hofman napsal(a):
>>>>> Hi,
>>>>>
>>>>> Please how is the module params pcm_notify supposed to be used, to do
>>>>> what the documentation says: Break capture when PCM 
>>>>> format/rate/channels
>>>>> changes?
>>>>>
>>>>> Breaking capture side operation when the playback side changes the
>>>>> params is very useful, but I cannot find a way to use this param
>>>>> properly. When the capture side is open, the playback side cannot 
>>>>> use a
>>>>> different parameter than the one currently used by the capture side 
>>>>> (the
>>>>> configuration space is limited)
>>>>
>>>> Really? Then it's a bug introduced by the last changes.
>>>>
>>>> If you look to sources:
>>>>
>>>>        if (get_notify(dpcm))
>>>>                  runtime->hw = loopback_pcm_hardware;
>>>>          else
>>>>                  runtime->hw = cable->hw;
>>>>
>>>> And:
>>>>
>>>>        if (!(cable->valid & ~(1 << substream->stream)) ||
>>>>              (get_setup(dpcm)->notify &&
>>>>               substream->stream == SNDRV_PCM_STREAM_PLAYBACK))
>>>>                  params_change(substream);
>>>>
>>>> So the functionality should be there.
>>>
>>> I am using older kernels (4.15 and 3.16), but this is an old 
>>> functionality.
>>>
>>> modprobe snd-aloop pcm_substreams=1 pcm_notify=1,1
>>>
>>
>> Please is there any way to solve this issue? Thanks a lot for your 
>> patience.
> 
> I can reproduce this. It appears that the driver should be fixed, but I 
> don't have a solution at the moment.
> 
> It seems that 898dfe4687f460ba337a01c11549f87269a13fa2 from Takashi 
> broke this functionality (tied the cable parameters more strictly, so 
> the playback cannot set freely own parameters for the pcm_notify=1 
> case). We need to find another way to detach capture stream in this case.
> 

Thanks a lot for your effort. I am afraid I cannot help with such 
design-level task.

BTW the sound design of snd-aloop allows reliable operation at 20MHz 
samplerate, it took just a period_max param change 
https://www.diyaudio.com/forums/equipment-and-tools/349239-support-samplerates-sw-analyzers.html#post6133979 
I will ask for considering a substantial samplerate range extension in a 
separate post :-)

Thanks again.

Best regards,

Pavel.