ALSA: usb-audio: move and add some comments
Also add a list of open topics.
Signed-off-by: Daniel Mack <daniel@caiaq.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/include/linux/usb/audio-v2.h b/include/linux/usb/audio-v2.h
index 716aebe..964cb60 100644
--- a/include/linux/usb/audio-v2.h
+++ b/include/linux/usb/audio-v2.h
@@ -18,6 +18,21 @@
/* v1.0 and v2.0 of this standard have many things in common. For the rest
* of the definitions, please refer to audio.h */
+/*
+ * bmControl field decoders
+ *
+ * From the USB Audio spec v2.0:
+ *
+ * bmaControls() is a (ch+1)-element array of 4-byte bitmaps,
+ * each containing a set of bit pairs. If a Control is present,
+ * it must be Host readable. If a certain Control is not
+ * present then the bit pair must be set to 0b00.
+ * If a Control is present but read-only, the bit pair must be
+ * set to 0b01. If a Control is also Host programmable, the bit
+ * pair must be set to 0b11. The value 0b10 is not allowed.
+ *
+ */
+
static inline bool uac2_control_is_readable(u32 bmControls, u8 control)
{
return (bmControls >> (control * 2)) & 0x1;