At Mon, 23 Apr 2012 19:36:06 +0100 (BST), Mark Hills wrote:
On Mon, 23 Apr 2012, Felix Homann wrote:
+/* This function allows for the creation of standard UAC controls.
- See the quirks for M-Audio FTUs or Ebox-44.
- If you don't want to set a TLV callback pass NULL.
- Since there doesn't seem to be a devices that needs a multichannel
- version, we keep it mono for simplicity.
- */
+static int snd_create_std_mono_ctl(struct usb_mixer_interface *mixer,
unsigned int unitid,unsigned int control,unsigned int cmask,int val_type,const char *name,snd_kcontrol_tlv_rw_t *tlv_callback)+{
- int err;
- struct usb_mixer_elem_info *cval;
- struct snd_kcontrol *kctl;
- cval = kzalloc(sizeof(*cval), GFP_KERNEL);
- if (!cval)
return -ENOMEM;- cval->id = unitid;
- cval->mixer = mixer;
- cval->val_type = val_type;
- cval->channels = 1;
- cval->control = control;
- cval->cmask = cmask;
- /* FIXME: Do we need this?
* The following values are for compatibility with* Ebox-44 mixer.* But the corresponding ebox-44 function says:* "Volume controls will override these values"** These values don't have any effect at all for* M-Audio FTUs.* So I think, we can safely omit the range settings here.*/- cval->min = 0;
- cval->max = 1;
- cval->res = 0;
- cval->dBmin = 0;
- cval->dBmax = 0;
When implementing the Ebox44 quirk, I found I needed this. The min and max would be automatically completed for the S16 values, but not for the mute buttons, so I defaulted to the range required for the BOOLEAN.
I was really hoping some one would explain this when I RFC'd the patch. But at that time the code was not part of some general-purpose function so it wasn't really an issue.
The reason is because get_min_max*() isn't called in the place you created these controls, and get_min_max() would be called only for integer volumes later even if uninitialized. A short cut for booleans.
Takashi