[alsa-devel] Getting a notification of snd_kcontrol value change, defined in codec, in machine driver
Hey,
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.
Thank you, Giedrius.
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
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?
On Sun, Jul 8, 2018 at 4:00 AM, Takashi Sakamoto o-takashi@sakamocchi.jp 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
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@sakamocchi.jp 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@alsa-project.org http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
participants (3)
-
Giedrius Trainavičius -
Takashi Iwai -
Takashi Sakamoto