[alsa-devel] [PATCH] alsa-lib/tlv: fix handling of raw value ranges

[Benoît Thébaudeau]

In case of a TLV dB range with all items having raw value ranges strictly within
the main raw value range reported by the driver, snd_tlv_convert_from_dB()
returned one of the main raw range boundaries, which was outside all dB range
items.

E.g.:
static const unsigned int bd3753x_vol_fader_gain_att_tlv[] = {
	TLV_DB_RANGE_HEAD(2),
	0, 0, TLV_DB_SCALE_ITEM(TLV_DB_GAIN_MUTE, 0, 1),
	48, 142, TLV_DB_SCALE_ITEM(-7900, 100, 0),
};
	SOC_SINGLE_TLV("Main Volume",
		       BD3753X_VOL_GAIN,
		       0, 255, 1, bd3753x_vol_fader_gain_att_tlv),

snd_tlv_convert_from_dB(tlv, 0, 255, 1500, &value, 1) returned 255 instead of
the expected 142.

or:
static const unsigned int max9850_tlv[] = {
	TLV_DB_RANGE_HEAD(4),
	0x18, 0x1f, TLV_DB_SCALE_ITEM(-7450, 400, 0),
	0x20, 0x33, TLV_DB_SCALE_ITEM(-4150, 200, 0),
	0x34, 0x37, TLV_DB_SCALE_ITEM(-150, 100, 0),
	0x38, 0x3f, TLV_DB_SCALE_ITEM(250, 50, 0),
};
SOC_SINGLE_TLV("Headphone Volume", MAX9850_VOLUME, 0, 0x3f, 1, max9850_tlv),

snd_tlv_convert_from_dB(tlv, 0, 0x3f, -7450, &value, 0) returned 0 instead of
the expected 0x18.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau at advansee.com>

--- alsa-lib/src/control/tlv.c
+++ alsa-lib/src/control/tlv.c
@@ -291,41 +291,37 @@ int snd_tlv_convert_from_dB(unsigned int
 {
 	switch (tlv[0]) {
 	case SND_CTL_TLVT_DB_RANGE: {
-		long dbmin, dbmax, prev_rangemax;
+		long dbmin, dbmax, prev_submax;
 		unsigned int pos, len;
 		len = int_index(tlv[1]);
-		if (len > MAX_TLV_RANGE_SIZE)
-			return -EINVAL;
-		if (snd_tlv_get_dB_range(tlv, rangemin, rangemax,
-					 &dbmin, &dbmax))
+		if (len < 6 || len > MAX_TLV_RANGE_SIZE)
 			return -EINVAL;
-		if (db_gain <= dbmin) {
-			*value = rangemin;
-			return 0;
-		} else if (db_gain >= dbmax) {
-			*value = rangemax;
-			return 0;
-		}
 		pos = 2;
-		prev_rangemax = 0;
-		while (pos + 4 <= len) {
-			rangemin = (int)tlv[pos];
-			rangemax = (int)tlv[pos + 1];
+		prev_submax = 0;
+		do {
+			long submin, submax;
+			submin = (int)tlv[pos];
+			submax = (int)tlv[pos + 1];
+			if (rangemax < submax)
+				submax = rangemax;
 			if (!snd_tlv_get_dB_range(tlv + pos + 2,
-						  rangemin, rangemax,
+						  submin, submax,
 						  &dbmin, &dbmax) &&
 			    db_gain >= dbmin && db_gain <= dbmax)
 				return snd_tlv_convert_from_dB(tlv + pos + 2,
-							       rangemin, rangemax,
+							       submin, submax,
 							       db_gain, value, xdir);
 			else if (db_gain < dbmin) {
-				*value = xdir ? rangemin : prev_rangemax;
+				*value = xdir || pos == 2 ? submin : prev_submax;
 				return 0;
 			}
-			prev_rangemax = rangemax;
+			prev_submax = submax;
+			if (rangemax == submax)
+				break;
 			pos += int_index(tlv[pos + 3]) + 4;
-		}
-		return -EINVAL;
+		} while (pos + 4 <= len);
+		*value = prev_submax;
+		return 0;
 	}
 	case SND_CTL_TLVT_DB_SCALE: {
 		int min, step, max;