Re: Question about struct snd_soc_dai() :: cpu_dai->codec

[Takashi Iwai <tiwai@suse.de>]

On Thu, 04 Aug 2016 15:39:40 +0200,
Takashi Sakamoto wrote:
> 
> 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?

Just grep try_module_get() and module_put() calls.


Takashi