ALSA: usb-mixer: parse descriptors with structs

Introduce a number of new structs for mixer, selector, feature and
processing units and some static inline helpers to access fields which
have dynamic offsets. Use them in mixer.c to parse the descriptors. This
is necessary for the upcoming audio v2 parsers.
Signed-off-by: Daniel Mack <daniel@caiaq.de>
Cc: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

include/linux/usb/audio.h

@@ -181,6 +181,125 @@ struct uac_feature_unit_descriptor_##ch {			\
 	__u8  iFeature;						\
 } __attribute__ ((packed))
 
+/* 4.3.2.3 Mixer Unit Descriptor */
+struct uac_mixer_unit_descriptor {
+	__u8 bLength;
+	__u8 bDescriptorType;
+	__u8 bDescriptorSubtype;
+	__u8 bUnitID;
+	__u8 bNrInPins;
+	__u8 baSourceID[];
+} __attribute__ ((packed));
+
+static inline __u8 uac_mixer_unit_bNrChannels(struct uac_mixer_unit_descriptor *desc)
+{
+	return desc->baSourceID[desc->bNrInPins];
+}
+
+static inline __u16 uac_mixer_unit_wChannelConfig(struct uac_mixer_unit_descriptor *desc)
+{
+	return (desc->baSourceID[desc->bNrInPins + 2] << 8) |
+		desc->baSourceID[desc->bNrInPins + 1];
+}
+
+static inline __u8 uac_mixer_unit_iChannelNames(struct uac_mixer_unit_descriptor *desc)
+{
+	return desc->baSourceID[desc->bNrInPins + 3];
+}
+
+static inline __u8 *uac_mixer_unit_bmControls(struct uac_mixer_unit_descriptor *desc)
+{
+	return &desc->baSourceID[desc->bNrInPins + 4];
+}
+
+static inline __u8 uac_mixer_unit_iMixer(struct uac_mixer_unit_descriptor *desc)
+{
+	__u8 *raw = (__u8 *) desc;
+	return raw[desc->bLength - 1];
+}
+
+/* 4.3.2.4 Selector Unit Descriptor */
+struct uac_selector_unit_descriptor {
+	__u8 bLength;
+	__u8 bDescriptorType;
+	__u8 bDescriptorSubtype;
+	__u8 bUintID;
+	__u8 bNrInPins;
+	__u8 baSourceID[];
+} __attribute__ ((packed));
+
+static inline __u8 uac_selector_unit_iSelector(struct uac_selector_unit_descriptor *desc)
+{
+	__u8 *raw = (__u8 *) desc;
+	return raw[desc->bLength - 1];
+}
+
+/* 4.3.2.5 Feature Unit Descriptor */
+struct uac_feature_unit_descriptor {
+	__u8 bLength;
+	__u8 bDescriptorType;
+	__u8 bDescriptorSubtype;
+	__u8 bUnitID;
+	__u8 bSourceID;
+	__u8 bControlSize;
+	__u8 bmaControls[0]; /* variable length */
+} __attribute__((packed));
+
+static inline __u8 uac_feature_unit_iFeature(struct uac_feature_unit_descriptor *desc)
+{
+	__u8 *raw = (__u8 *) desc;
+	return raw[desc->bLength - 1];
+}
+
+/* 4.3.2.6 Processing Unit Descriptors */
+struct uac_processing_unit_descriptor {
+	__u8 bLength;
+	__u8 bDescriptorType;
+	__u8 bDescriptorSubtype;
+	__u8 bUnitID;
+	__u16 wProcessType;
+	__u8 bNrInPins;
+	__u8 baSourceID[];
+} __attribute__ ((packed));
+
+static inline __u8 uac_processing_unit_bNrChannels(struct uac_processing_unit_descriptor *desc)
+{
+	return desc->baSourceID[desc->bNrInPins];
+}
+
+static inline __u16 uac_processing_unit_wChannelConfig(struct uac_processing_unit_descriptor *desc)
+{
+	return (desc->baSourceID[desc->bNrInPins + 2] << 8) |
+		desc->baSourceID[desc->bNrInPins + 1];
+}
+
+static inline __u8 uac_processing_unit_iChannelNames(struct uac_processing_unit_descriptor *desc)
+{
+	return desc->baSourceID[desc->bNrInPins + 3];
+}
+
+static inline __u8 uac_processing_unit_bControlSize(struct uac_processing_unit_descriptor *desc)
+{
+	return desc->baSourceID[desc->bNrInPins + 4];
+}
+
+static inline __u8 *uac_processing_unit_bmControls(struct uac_processing_unit_descriptor *desc)
+{
+	return &desc->baSourceID[desc->bNrInPins + 5];
+}
+
+static inline __u8 uac_processing_unit_iProcessing(struct uac_processing_unit_descriptor *desc)
+{
+	__u8 control_size = uac_processing_unit_bControlSize(desc);
+	return desc->baSourceID[desc->bNrInPins + control_size];
+}
+
+static inline __u8 *uac_processing_unit_specific(struct uac_processing_unit_descriptor *desc)
+{
+	__u8 control_size = uac_processing_unit_bControlSize(desc);
+	return &desc->baSourceID[desc->bNrInPins + control_size + 1];
+}
+
 /* 4.5.2 Class-Specific AS Interface Descriptor */
 struct uac_as_header_descriptor_v1 {
 	__u8  bLength;			/* in bytes: 7 */
@@ -315,16 +434,6 @@ struct uac_iso_endpoint_descriptor {
 
 /* A.10.2 Feature Unit Control Selectors */
 
-struct uac_feature_unit_descriptor {
-	__u8 bLength;
-	__u8 bDescriptorType;
-	__u8 bDescriptorSubtype;
-	__u8 bUnitID;
-	__u8 bSourceID;
-	__u8 bControlSize;
-	__u8 controls[0]; /* variable length */
-} __attribute__((packed));
-
 #define UAC_FU_CONTROL_UNDEFINED	0x00
 #define UAC_MUTE_CONTROL		0x01
 #define UAC_VOLUME_CONTROL		0x02