On Sun, 08 Jul 2018 09:16:48 +0200, Giedrius Trainavičius wrote: > > I would like to 'hook into' controls defined in a codec driver from my > machine driver - so I don't really have access to how these controls get > created in the first place. > > Would it be possible to iterate in my machine driver through all the > controls defined by the codec, memorize the original 'put' callback, > override it with my own which performs the task I need and calls the > original put callback? It's feasible, the virtual master (vmaster) code does something like that, for example. But no generic framework is provided, so far. Takashi > > On Sun, Jul 8, 2018 at 4:00 AM, Takashi Sakamoto <o-takashi@xxxxxxxxxxxxx> > wrote: > > > Hi, > > > > On Jul 8 2018 08:10, Giedrius Trainavičius wrote: > > > >> What would be the best way in machine driver to learn about changes of > >> alsa > >> mixer control values? The controls are defined in the codec driver. > >> > >> The intended use case would be to use the current volume setting for the > >> codec on the board to forward to a dedicated microcontroller for visual > >> feedback. > >> > >> I am aware that this could be bridged over via a user space program, but I > >> will have to forward the current PCM stream format to the MCU anyway from > >> hw_params, so ideally I would like all of this functionality contained in > >> the machine driver. > >> > > > > By assigning a function to 'struct snd_kcontrol.put', in-kernel drivers > > can receive any notification as a callback at changing value array of a > > control element set including handled conntrol element. When calling > > snd_ctl_new(), passing proper data for an argument of 'struct > > snd_kcontrol_new'. > > > > I note that for userspace applications, ALSA control core supports > > notification mechanism for this purpose by typical I/O handling in UNIX > > environment. With alsa-lib, at first, call 'snd_ctl_subscribe_events()', > > then listen to file descriptor for opened ALSA control character device (or > > call 'snd_ctl_wait()'). When any events are emitted, the applications can > > read data of 'struct snd_ctl_event' from the descriptor and handle the > > notification by parsing the data. > > > > > > Regards > > > > Takashi Sakamoto > > > _______________________________________________ > Alsa-devel mailing list > Alsa-devel@xxxxxxxxxxxxxxxx > http://mailman.alsa-project.org/mailman/listinfo/alsa-devel _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
