[alsa-devel] Hardware events
Hello,
For some hardware devices (for instance the ThinkPad EC) the volume can be changed by (only) hardware buttons. Changes in the the hardware mixers are notified in the driver via the function "snd_ctl_notify" with the mask SNDRV_CLT_EVENT_MASK_VALUE. For notification of volume changes to the users of the system, an OSD can be used. To implement such a OSD, it must be possible to respond to changes done by the hardware.
This raises the following question: is it possible to detect the events originating from the hardware in the functions that handle the callbacks (set via snd_mixer_elem_set_callback/snd_hctl_elem_set_callback)? This would allow to implement an OSD that only responds to the hardware buttons and that would ignore events originating from "software".
Thanks
Rolf Theunissen wrote:
For some hardware devices (for instance the ThinkPad EC) the volume can be changed by (only) hardware buttons. ... This raises the following question: is it possible to detect the events originating from the hardware in the functions that handle the callbacks (set via snd_mixer_elem_set_callback/snd_hctl_elem_set_callback)? This would allow to implement an OSD that only responds to the hardware buttons and that would ignore events originating from "software".
The control notifications are for all changes of the control.
If it is not possible to change the volume in software, then the driver must not set the control to be writable.
Regards, Clemens
Clemens Ladisch wrote:
Rolf Theunissen wrote:
For some hardware devices (for instance the ThinkPad EC) the volume can be changed by (only) hardware buttons. ... This raises the following question: is it possible to detect the events originating from the hardware in the functions that handle the callbacks (set via snd_mixer_elem_set_callback/snd_hctl_elem_set_callback)? This would allow to implement an OSD that only responds to the hardware buttons and that would ignore events originating from "software".
The control notifications are for all changes of the control.
If it is not possible to change the volume in software, then the driver must not set the control to be writable.
Regards, Clemens
The issue is not that the driver should be writable or not. Even, if the volume is read only, an OSD can be shown for any event. However when the volume can be set both in hardware and in software, the end-user will expect different behavior. For instance, if the user changes the volume in a music player application, no OSD should be shown as this clutters the interface. But if the volume is changed from the hardware a OSD should be shown.
I don't know if a ticket should be opened for this issue.
Regards, Rolf
Rolf Theunissen wrote:
Clemens Ladisch wrote:
The control notifications are for all changes of the control.
If it is not possible to change the volume in software, then the driver must not set the control to be writable.
The issue is not that the driver should be writable or not. Even, if the volume is read only, an OSD can be shown for any event. However when the volume can be set both in hardware and in software, the end-user will expect different behavior.
The control notifications are for all changes of the control.
If you want to treat hardware-originated changes differently, you have to send an additional, different notification for the OSD tool.
Usually, such volume change buttons are just treated as input devices, and software is then expected to change the actual mixer control, but this doesn't work if the hardware affects the control directly.
Regards, Clemens
participants (2)
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Clemens Ladisch -
Rolf Theunissen