[alsa-devel] [PATCH v3 2/4] ALSA: usb-audio: Add usb_mixer_elem_enum_info

[Takashi Iwai]

At Wed, 29 Oct 2014 15:56:01 -0500,
Chris J Arges wrote:
> 
> Add structure to hold enumeration control information and in addition add it
> to the usb_mixer_elem_info structure. This allows this structure to be more
> easily reused.

Since this information is specific to Scarlett, we don't have to put
in the common place.  Instead, define this locally in
mixer_scarlett.c, redefine the mixer info struct like

	struct scarlett_mixer_elem_info {
		struct usb_mixer_elem_info head;
		const struct scarlett_enum_info *opt;
	};

and allocate this struct, and cast between usb_mixer_elem_info and
scarlett_mixer_elem_info.

Another way would be to add a pointer to usb_mixer_elem_info, but just
an opaque void pointer instead of a specific type.

	struct usb_mixer_elem_info {
		....
		void *private_data;
	};

I don't mind either way.


Takashi


> 
> Signed-off-by: Chris J Arges <chris.j.arges at canonical.com>
> ---
>  sound/usb/mixer.h | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/sound/usb/mixer.h b/sound/usb/mixer.h
> index 73b1f64..cf3967a4 100644
> --- a/sound/usb/mixer.h
> +++ b/sound/usb/mixer.h
> @@ -36,10 +36,17 @@ enum {
>  	USB_MIXER_U16,
>  };
>  
> +struct usb_mixer_elem_enum_info {
> +	int start;
> +	int len;
> +	const char * const *names;
> +};
> +
>  struct usb_mixer_elem_info {
>  	struct usb_mixer_interface *mixer;
>  	struct usb_mixer_elem_info *next_id_elem; /* list of controls with same id */
>  	struct snd_ctl_elem_id *elem_id;
> +	const struct usb_mixer_elem_enum_info *opt; /* enum control info */
>  	unsigned int id;
>  	unsigned int control;	/* CS or ICN (high byte) */
>  	unsigned int cmask; /* channel mask bitmap: 0 = master */
> -- 
> 2.1.0
>