Hello, I want to enable/disable some mixer controls based on state of another control (switching between limiter and AGC mode). So I (re)set the SNDRV_CTL_ELEM_ACCESS_INACTIVE flag in kctl->vd[0].access and then call snd_ctl_notify(card, SNDRV_CTL_EVENT_MASK_INFO, &kctl->id); Everyting from ctl_put() mixer callback.
When changing the control value in alsamixer, it crashes with: alsamixer: simple.c:948: snd_mixer_selem_get_enum_item: Assertion `(elem)->type == SND_MIXER_ELEM_SIMPLE' failed.
When the snd_ctl_notify() call is commented-out, it does not crash.
There is snd_ctl_activate_id() function in sound/core/control.c (not used by any driver, btw.) which does the same, protected by card->controls_rwsem. However, it locks up on that semaphore when called from the mixer callback.
Oxygen/Xonar WM8776 driver is doing the same thing - I wonder if I'm doing something wrong or if that driver crashes alsamixer too?
Is there any way to do this properly?