Dimitris Papastamos wrote:
Add a function to dynamically update a given control. If the control does not already exist, a third parameter is used to determine whether to actually add that control. This is useful in cases where downloadable firmware at runtime can add or update existing controls.
- Updates the control instance created via snd_ctl_new() or
- snd_ctl_new1() of the given card.
This description was copied from snd_ctl_add(), and the "created ..." part isn't really useful here.
It should be mentioned that the old control is destroyed, because some drivers store volatile state in the control's private_data/_value, or keep a pointer to the control('s ID) to be able to call snd_ctl_notify() for it later.
- Returns zero if successful, or a negative error code on failure.
superfluous empty line
+int snd_ctl_update(struct snd_card *card, struct snd_kcontrol *kcontrol,
int add_on_update)
add_on_update should be bool
- up_write(&card->controls_rwsem);
- ret = snd_ctl_add(card, kcontrol);
Doing this outside the semaphore doesn't look good.
I wonder whether snd_ctl_add() is the right function to use, because it will assign a different numid event if the control didn't change.
A separate patch needs to be made to make ALSA Mixer cope with this.
What happens?
Regards, Clemens