Re: [PATCH 1/5] Unify M-Audio Fast Track Ultra and Ebox-44 mixer quirks.

[Mark Hills <mark@pogo.org.uk>]

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.

-- 
Mark