ALSA: tlv: compute TLV_*_ITEM lengths automatically

Add helper macros with a little bit of preprocessor magic to
automatically compute the length of a TLV item.  This lets us avoid
having to compute this by hand, and will allow to use items that do
not use a fixed length.
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

include/sound/tlv.h

@@ -38,21 +38,26 @@
 #define SNDRV_CTL_TLVT_DB_MINMAX 4	/* dB scale with min/max */
 #define SNDRV_CTL_TLVT_DB_MINMAX_MUTE 5	/* dB scale with min/max with mute */
 
+#define TLV_ITEM(type, ...) \
+	(type), TLV_LENGTH(__VA_ARGS__), __VA_ARGS__
+#define TLV_LENGTH(...) \
+	((unsigned int)sizeof((const unsigned int[]) { __VA_ARGS__ }))
+
 #define TLV_DB_SCALE_MASK	0xffff
 #define TLV_DB_SCALE_MUTE	0x10000
 #define TLV_DB_SCALE_ITEM(min, step, mute)			\
-	SNDRV_CTL_TLVT_DB_SCALE, 2 * sizeof(unsigned int),	\
-	(min), ((step) & TLV_DB_SCALE_MASK) | ((mute) ? TLV_DB_SCALE_MUTE : 0)
+	TLV_ITEM(SNDRV_CTL_TLVT_DB_SCALE,			\
+		 (min),					\
+		 ((step) & TLV_DB_SCALE_MASK) |		\
+			((mute) ? TLV_DB_SCALE_MUTE : 0))
 #define DECLARE_TLV_DB_SCALE(name, min, step, mute) \
 	unsigned int name[] = { TLV_DB_SCALE_ITEM(min, step, mute) }
 
 /* dB scale specified with min/max values instead of step */
 #define TLV_DB_MINMAX_ITEM(min_dB, max_dB)			\
-	SNDRV_CTL_TLVT_DB_MINMAX, 2 * sizeof(unsigned int),	\
-	(min_dB), (max_dB)
+	TLV_ITEM(SNDRV_CTL_TLVT_DB_MINMAX, (min_dB), (max_dB))
 #define TLV_DB_MINMAX_MUTE_ITEM(min_dB, max_dB)			\
-	SNDRV_CTL_TLVT_DB_MINMAX_MUTE, 2 * sizeof(unsigned int),	\
-	(min_dB), (max_dB)
+	TLV_ITEM(SNDRV_CTL_TLVT_DB_MINMAX_MUTE, (min_dB), (max_dB))
 #define DECLARE_TLV_DB_MINMAX(name, min_dB, max_dB) \
 	unsigned int name[] = { TLV_DB_MINMAX_ITEM(min_dB, max_dB) }
 #define DECLARE_TLV_DB_MINMAX_MUTE(name, min_dB, max_dB) \
@@ -60,8 +65,7 @@
 
 /* linear volume between min_dB and max_dB (.01dB unit) */
 #define TLV_DB_LINEAR_ITEM(min_dB, max_dB)		    \
-	SNDRV_CTL_TLVT_DB_LINEAR, 2 * sizeof(unsigned int), \
-	(min_dB), (max_dB)
+	TLV_ITEM(SNDRV_CTL_TLVT_DB_LINEAR, (min_dB), (max_dB))
 #define DECLARE_TLV_DB_LINEAR(name, min_dB, max_dB)	\
 	unsigned int name[] = { TLV_DB_LINEAR_ITEM(min_dB, max_dB) }