[alsa-devel] Question about struct snd_soc_dai() :: cpu_dai->codec

[Takashi Sakamoto]

On Aug 4 2016 21:27, Takashi Iwai wrote:
> On Thu, 04 Aug 2016 14:12:09 +0200,
> Takashi Sakamoto wrote:
>>
>> On Aug 4 2016 19:28, Mark Brown wrote:
>>> On Thu, Aug 04, 2016 at 12:17:57PM +0900, Takashi Sakamoto wrote:
>>>> On Jul 30 2016 07:08, Mark Brown wrote:
>>>
>>>>> The card should be deinstantiated and reinstantiated whenever a
>>>>> component driver unbinds and rebinds (respectively).  You'd need to
>>>>> completely deregister the card to change the list of things it's
>>>>> expecting currently.
>>>
>>>> In a point of application interfaces, I guess that current implementation of
>>>> ALSA soc part includes a bug that it's possible to unload codec or component
>>>> modules when any ALSA character devices are opened. The framework has no
>>>> codes to manage reference counting of character devices or loaded codecs,
>>>> components.
>>>
>>> Yes, exactly - we don't cope very well with that situation and we really
>>> ought to but since it's hard to trigger without trying in practice it's
>>> never been a priority.
>>
>> Ugly... completely ugly idea for user space applications and operating
>> system... It's better for developers for ALSA soc part to pay enough
>> attention not only to their hardwares but also to application interfaces.
>>
>> Please assume that a loaded module for SoC's sound interface which
>> supports Jack detection, and pulseaudio runs on the system. Then,
>> typically, the process listen to ALSA ctrl character device for Jack
>> detection.
>>
>> In this case, when modules for codec or component are unloaded, what
>> happends?
> 
> You can't unload.  The module unload is already protected by the
> proper module refcounting.

Hm. For my information, could you please show call graph to increment
the reference counter of codec/component modules when modules for SoC's
sound interfaces refer to them?


Regards

Takashi Sakamoto