Get rid of the IGMPV3_MRC macro and use the igmpv3_mrt() API to
calculate the Max Resp Time from the Maximum Response Code.

Similarly, for IGMPV3_QQIC, use the igmpv3_qqi() API to calculate
the Querier's Query Interval from the QQIC field.

Signed-off-by: Ujjal Roy <royujjal@gmail.com>
---
 include/linux/igmp.h      | 78 +++++++++++++++++++++++++++++++++++----
 net/bridge/br_multicast.c |  2 +-
 net/ipv4/igmp.c           |  6 +--
 3 files changed, 74 insertions(+), 12 deletions(-)

diff --git a/include/linux/igmp.h b/include/linux/igmp.h
index 073b30a9b850..3c12c0a63492 100644
--- a/include/linux/igmp.h
+++ b/include/linux/igmp.h
@@ -92,15 +92,77 @@ struct ip_mc_list {
 	struct rcu_head		rcu;
 };
 
+/* RFC3376, relevant sections:
+ *  - 4.1.1. Maximum Response Code
+ *  - 4.1.7. QQIC (Querier's Query Interval Code)
+ *
+ * If Max Resp Code >= 128, Max Resp Code represents a floating-point
+ * value as follows:
+ * If QQIC >= 128, QQIC represents a floating-point value as follows:
+ *
+ *  0 1 2 3 4 5 6 7
+ * +-+-+-+-+-+-+-+-+
+ * |1| exp | mant  |
+ * +-+-+-+-+-+-+-+-+
+ */
+#define IGMPV3_FP_EXP(value)		(((value) >> 4) & 0x07)
+#define IGMPV3_FP_MAN(value)		((value) & 0x0f)
+
+/* IGMPV3 floating-point exponential field threshold */
+#define IGMPV3_EXP_MIN_THRESHOLD	128
+
 /* V3 exponential field decoding */
-#define IGMPV3_MASK(value, nb) ((nb)>=32 ? (value) : ((1<<(nb))-1) & (value))
-#define IGMPV3_EXP(thresh, nbmant, nbexp, value) \
-	((value) < (thresh) ? (value) : \
-        ((IGMPV3_MASK(value, nbmant) | (1<<(nbmant))) << \
-         (IGMPV3_MASK((value) >> (nbmant), nbexp) + (nbexp))))
-
-#define IGMPV3_QQIC(value) IGMPV3_EXP(0x80, 4, 3, value)
-#define IGMPV3_MRC(value) IGMPV3_EXP(0x80, 4, 3, value)
+
+/*
+ * IGMPv3 QQI/MRT 8-bit exponential field decode.
+ *
+ * RFC3376, 4.1.1 & 4.1.7. defines the decoding formula:
+ *      0 1 2 3 4 5 6 7
+ *     +-+-+-+-+-+-+-+-+
+ *     |1| exp | mant  |
+ *     +-+-+-+-+-+-+-+-+
+ * Max Resp Time = (mant | 0x10) << (exp + 3)
+ * QQI = (mant | 0x10) << (exp + 3)
+ */
+static inline unsigned long igmpv3_exp_field_decode(const u8 code)
+{
+	/* RFC3376, relevant sections:
+	 *  - 4.1.1. Maximum Response Code
+	 *  - 4.1.7. QQIC (Querier's Query Interval Code)
+	 */
+	if (code < IGMPV3_EXP_MIN_THRESHOLD) {
+		return (unsigned long)code;
+	} else {
+		unsigned long mc_man, mc_exp;
+
+		mc_exp = IGMPV3_FP_EXP(code);
+		mc_man = IGMPV3_FP_MAN(code);
+
+		return ((mc_man | 0x10) << (mc_exp + 3));
+	}
+}
+
+/* Calculate Max Resp Time from Maximum Response Code */
+static inline unsigned long igmpv3_mrt(const struct igmpv3_query *ih3)
+{
+	/* RFC3376, relevant sections:
+	 *  - 4.1.1. Maximum Response Code
+	 *  - 8.3. Query Response Interval
+	 */
+	return igmpv3_exp_field_decode(ih3->code);
+}
+
+/* Calculate Querier's Query Interval from Querier's Query Interval Code */
+static inline unsigned long igmpv3_qqi(const struct igmpv3_query *ih3)
+{
+	/* RFC3376, relevant sections:
+	 *  - 4.1.7. QQIC (Querier's Query Interval Code)
+	 *  - 8.2. Query Interval
+	 *  - 8.12. Older Version Querier Present Timeout
+	 *    (the [Query Interval] in the last Query received)
+	 */
+	return igmpv3_exp_field_decode(ih3->qqic);
+}
 
 static inline int ip_mc_may_pull(struct sk_buff *skb, unsigned int len)
 {
diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index 881d866d687a..9fec76e887bc 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -3518,7 +3518,7 @@ static void br_ip4_multicast_query(struct net_bridge_mcast *brmctx,
 			goto out;
 
 		max_delay = ih3->code ?
-			    IGMPV3_MRC(ih3->code) * (HZ / IGMP_TIMER_SCALE) : 1;
+			    igmpv3_mrt(ih3) * (HZ / IGMP_TIMER_SCALE) : 1;
 	} else {
 		goto out;
 	}
diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index a674fb44ec25..8c6102737096 100644
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -991,7 +991,7 @@ static bool igmp_heard_query(struct in_device *in_dev, struct sk_buff *skb,
 		 * different encoding. We use the v3 encoding as more likely
 		 * to be intended in a v3 query.
 		 */
-		max_delay = IGMPV3_MRC(ih3->code)*(HZ/IGMP_TIMER_SCALE);
+		max_delay = igmpv3_mrt(ih3)*(HZ/IGMP_TIMER_SCALE);
 		if (!max_delay)
 			max_delay = 1;	/* can't mod w/ 0 */
 	} else { /* v3 */
@@ -1006,7 +1006,7 @@ static bool igmp_heard_query(struct in_device *in_dev, struct sk_buff *skb,
 			ih3 = igmpv3_query_hdr(skb);
 		}
 
-		max_delay = IGMPV3_MRC(ih3->code)*(HZ/IGMP_TIMER_SCALE);
+		max_delay = igmpv3_mrt(ih3)*(HZ/IGMP_TIMER_SCALE);
 		if (!max_delay)
 			max_delay = 1;	/* can't mod w/ 0 */
 		WRITE_ONCE(in_dev->mr_maxdelay, max_delay);
@@ -1016,7 +1016,7 @@ static bool igmp_heard_query(struct in_device *in_dev, struct sk_buff *skb,
 		 * configured value.
 		 */
 		in_dev->mr_qrv = ih3->qrv ?: READ_ONCE(net->ipv4.sysctl_igmp_qrv);
-		in_dev->mr_qi = IGMPV3_QQIC(ih3->qqic)*HZ ?: IGMP_QUERY_INTERVAL;
+		in_dev->mr_qi = igmpv3_qqi(ih3)*HZ ?: IGMP_QUERY_INTERVAL;
 
 		/* RFC3376, 8.3. Query Response Interval:
 		 * The number of seconds represented by the [Query Response
-- 
2.43.0

Rename mldv2_mrc() to mldv2_mrd() as it used to calculate
the Maximum Response Delay from the Maximum Response Code.

Introduce a new API mldv2_qqi() to define the existing
calculation logic of QQI from QQIC. This also organizes
the existing mld_update_qi() API.

Added by e3f5b1704 ("net: ipv6: mld: get rid of MLDV2_MRC and simplify calculation").

Signed-off-by: Ujjal Roy <royujjal@gmail.com>
---
 include/net/mld.h         | 64 +++++++++++++++++++++++++++++++++------
 net/bridge/br_multicast.c |  2 +-
 net/ipv6/mcast.c          | 19 ++----------
 3 files changed, 58 insertions(+), 27 deletions(-)

diff --git a/include/net/mld.h b/include/net/mld.h
index c07359808493..5e093f9c75d9 100644
--- a/include/net/mld.h
+++ b/include/net/mld.h
@@ -89,29 +89,73 @@ struct mld2_query {
 #define MLDV2_QQIC_EXP(value)	(((value) >> 4) & 0x07)
 #define MLDV2_QQIC_MAN(value)	((value) & 0x0f)
 
-#define MLD_EXP_MIN_LIMIT	32768UL
-#define MLDV1_MRD_MAX_COMPAT	(MLD_EXP_MIN_LIMIT - 1)
+#define MLD_QQIC_MIN_THRESHOLD	128
+#define MLD_MRC_MIN_THRESHOLD	32768UL
+#define MLDV1_MRD_MAX_COMPAT	(MLD_MRC_MIN_THRESHOLD - 1)
 
 #define MLD_MAX_QUEUE		8
 #define MLD_MAX_SKBS		32
 
-static inline unsigned long mldv2_mrc(const struct mld2_query *mlh2)
-{
-	/* RFC3810, 5.1.3. Maximum Response Code */
-	unsigned long ret, mc_mrc = ntohs(mlh2->mld2q_mrc);
+/* V2 exponential field decoding */
 
-	if (mc_mrc < MLD_EXP_MIN_LIMIT) {
-		ret = mc_mrc;
+/* Calculate Maximum Response Delay from Maximum Response Code
+ *
+ * RFC3810, 5.1.3. defines the decoding formula:
+ *      0 1 2 3 4 5 6 7 8 9 A B C D E F
+ *     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *     |1| exp |          mant         |
+ *     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * Maximum Response Delay = (mant | 0x1000) << (exp+3)
+ */
+static inline unsigned long mldv2_mrd(const struct mld2_query *mlh2)
+{
+	/* RFC3810, relevant sections:
+	 *  - 5.1.3. Maximum Response Code
+	 *  - 9.3. Query Response Interval
+	 */
+	unsigned long mc_mrc = ntohs(mlh2->mld2q_mrc);
+
+	if (mc_mrc < MLD_MRC_MIN_THRESHOLD) {
+		return mc_mrc;
 	} else {
 		unsigned long mc_man, mc_exp;
 
 		mc_exp = MLDV2_MRC_EXP(mc_mrc);
 		mc_man = MLDV2_MRC_MAN(mc_mrc);
 
-		ret = (mc_man | 0x1000) << (mc_exp + 3);
+		return ((mc_man | 0x1000) << (mc_exp + 3));
 	}
+}
 
-	return ret;
+/* Calculate Querier's Query Interval from Querier's Query Interval Code
+ *
+ * RFC3810, 5.1.9. defines the decoding formula:
+ *      0 1 2 3 4 5 6 7
+ *     +-+-+-+-+-+-+-+-+
+ *     |1| exp | mant  |
+ *     +-+-+-+-+-+-+-+-+
+ * QQI = (mant | 0x10) << (exp + 3)
+ */
+static inline unsigned long mldv2_qqi(const struct mld2_query *mlh2)
+{
+	/* RFC3810, relevant sections:
+	 *  - 5.1.9. QQIC (Querier's Query Interval Code)
+	 *  - 9.2. Query Interval
+	 *  - 9.12. Older Version Querier Present Timeout
+	 *    (the [Query Interval] in the last Query received)
+	 */
+	unsigned long qqic = mlh2->mld2q_qqic;
+
+	if (qqic < MLD_QQIC_MIN_THRESHOLD) {
+		return qqic;
+	} else {
+		unsigned long mc_man, mc_exp;
+
+		mc_exp = MLDV2_QQIC_EXP(qqic);
+		mc_man = MLDV2_QQIC_MAN(qqic);
+
+		return ((mc_man | 0x10) << (mc_exp + 3));
+	}
 }
 
 #endif
diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index 9fec76e887bc..1438c023db62 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -3606,7 +3606,7 @@ static int br_ip6_multicast_query(struct net_bridge_mcast *brmctx,
 		    mld2q->mld2q_suppress)
 			goto out;
 
-		max_delay = max(msecs_to_jiffies(mldv2_mrc(mld2q)), 1UL);
+		max_delay = max(msecs_to_jiffies(mldv2_mrd(mld2q)), 1UL);
 	}
 
 	is_general_query = group && ipv6_addr_any(group);
diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
index 3330adcf26db..6ddc18ac59b9 100644
--- a/net/ipv6/mcast.c
+++ b/net/ipv6/mcast.c
@@ -1315,20 +1315,7 @@ static void mld_update_qi(struct inet6_dev *idev,
 	 *  - 9.12. Older Version Querier Present Timeout
 	 *    (the [Query Interval] in the last Query received)
 	 */
-	unsigned long mc_qqi;
-
-	if (mlh2->mld2q_qqic < 128) {
-		mc_qqi = mlh2->mld2q_qqic;
-	} else {
-		unsigned long mc_man, mc_exp;
-
-		mc_exp = MLDV2_QQIC_EXP(mlh2->mld2q_qqic);
-		mc_man = MLDV2_QQIC_MAN(mlh2->mld2q_qqic);
-
-		mc_qqi = (mc_man | 0x10) << (mc_exp + 3);
-	}
-
-	idev->mc_qi = mc_qqi * HZ;
+	idev->mc_qi = mldv2_qqi(mlh2) * HZ;
 }
 
 static void mld_update_qri(struct inet6_dev *idev,
@@ -1338,7 +1325,7 @@ static void mld_update_qri(struct inet6_dev *idev,
 	 *  - 5.1.3. Maximum Response Code
 	 *  - 9.3. Query Response Interval
 	 */
-	idev->mc_qri = msecs_to_jiffies(mldv2_mrc(mlh2));
+	idev->mc_qri = msecs_to_jiffies(mldv2_mrd(mlh2));
 }
 
 static int mld_process_v1(struct inet6_dev *idev, struct mld_msg *mld,
@@ -1390,7 +1377,7 @@ static int mld_process_v1(struct inet6_dev *idev, struct mld_msg *mld,
 static void mld_process_v2(struct inet6_dev *idev, struct mld2_query *mld,
 			   unsigned long *max_delay)
 {
-	*max_delay = max(msecs_to_jiffies(mldv2_mrc(mld)), 1UL);
+	*max_delay = max(msecs_to_jiffies(mldv2_mrd(mld)), 1UL);
 
 	mld_update_qrv(idev, mld);
 	mld_update_qi(idev, mld);
-- 
2.43.0

In IGMP, QQIC and MRC fields are not currently encoded
when generating query packets. Since the receiver of the
query interprets these fields using the IGMPv3 floating-
point decoding logic, any raw interval value that exceeds
the linear threshold is currently parsed incorrectly as
an exponential value, leading to an incorrect interval
calculation.

Encode and assign the corresponding protocol fields during
query generation. Introduce the logic to dynamically
calculate the exponent and mantissa using bit-scan (fls).
This ensures QQIC and MRC fields (8-bit) are properly
encoded when transmitting query packets with intervals
that exceed their respective linear threshold value of
128 (for QQI/MRT).

RFC 3376: if QQIC/MRC >= 128, the QQIC/MRC field represents
a floating-point value as follows:
     0 1 2 3 4 5 6 7
    +-+-+-+-+-+-+-+-+
    |1| exp | mant  |
    +-+-+-+-+-+-+-+-+

Signed-off-by: Ujjal Roy <royujjal@gmail.com>
---
 include/linux/igmp.h      | 80 +++++++++++++++++++++++++++++++++++++++
 net/bridge/br_multicast.c | 14 +++----
 2 files changed, 86 insertions(+), 8 deletions(-)

diff --git a/include/linux/igmp.h b/include/linux/igmp.h
index 3c12c0a63492..3a4e9cec3959 100644
--- a/include/linux/igmp.h
+++ b/include/linux/igmp.h
@@ -110,6 +110,86 @@ struct ip_mc_list {
 
 /* IGMPV3 floating-point exponential field threshold */
 #define IGMPV3_EXP_MIN_THRESHOLD	128
+/* Max representable (mant = 0xF, exp = 7) -> 31744 */
+#define IGMPV3_EXP_MAX_THRESHOLD	31744
+
+/* V3 exponential field encoding */
+
+/*
+ * IGMPv3 QQIC/MRC 8-bit exponential field encode.
+ *
+ * RFC3376 defines only the decoding formula:
+ * QQI/MRT = (mant | 0x10) << (exp + 3)
+ *
+ * but does NOT define the encoding procedure. To derive exponent:
+ *
+ * For any value of mantissa and exponent, the decoding formula
+ * indicates that the "hidden bit" (0x10) is shifted 4 bits left
+ * to sit above the 4-bit mantissa. The RFC again shifts this
+ * entire block left by (exp + 3) to reconstruct the value.
+ * So, 'hidden bit' is the MSB which is shifted by (4 + exp + 3).
+ *
+ * Total left shift of the 'hidden bit' = 4 + (exp + 3) = exp + 7.
+ * This is the MSB at the 0-based bit position: (exp + 7).
+ * Since fls() is 1-based, fls(value) - 1 = exp + 7.
+ *
+ * Therefore:
+ *     exp  = fls(value) - 8
+ *     mant = (value >> (exp + 3)) & 0x0F
+ *
+ * Final encoding formula:
+ *     0x80 | (exp << 4) | mant
+ *
+ * Example (value = 3200):
+ *  0               1
+ *  0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |0 0 0 0 1 1 0 0 1 0 0 0 0 0 0 0| (value = 3200)
+ * |        ^-^-mant^ ^..(exp+3)..^| exp = 4, mant = 9
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *
+ * Encoded:
+ *   0x80 | (4 << 4) | 9 = 0xC9
+ */
+static inline u8 igmpv3_exp_field_encode(unsigned long value)
+{
+	u8 mc_exp, mc_man;
+
+	/* RFC3376: QQIC/MRC < 128 is literal */
+	if (value < IGMPV3_EXP_MIN_THRESHOLD)
+		return (u8)value;
+
+	/* Saturate at max representable (mant = 0xF, exp = 7) -> 31744 */
+	if (value >= IGMPV3_EXP_MAX_THRESHOLD)
+		return 0xFF;
+
+	mc_exp  = (u8)(fls(value) - 8);
+	mc_man = (u8)((value >> (mc_exp + 3)) & 0x0F);
+
+	return 0x80 | (mc_exp << 4) | mc_man;
+}
+
+/* Calculate Maximum Response Code from Max Resp Time */
+static inline u8 igmpv3_mrc(unsigned long mrt)
+{
+	/* RFC3376, relevant sections:
+	 *  - 4.1.1. Maximum Response Code
+	 *  - 8.3. Query Response Interval
+	 */
+	return igmpv3_exp_field_encode(mrt);
+}
+
+/* Calculate Querier's Query Interval Code from Query Interval */
+static inline u8 igmpv3_qqic(unsigned long qi)
+{
+	/* RFC3376, relevant sections:
+	 *  - 4.1.7. QQIC (Querier's Query Interval Code)
+	 *  - 8.2. Query Interval
+	 *  - 8.12. Older Version Querier Present Timeout
+	 *    (the [Query Interval] in the last Query received)
+	 */
+	return igmpv3_exp_field_encode(qi);
+}
 
 /* V3 exponential field decoding */
 
diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index 1438c023db62..27010744d7ae 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -934,12 +934,12 @@ static struct sk_buff *br_ip4_multicast_alloc_query(struct net_bridge_mcast *brm
 	size_t pkt_size, igmp_hdr_size;
 	unsigned long now = jiffies;
 	struct igmpv3_query *ihv3;
+	unsigned long lmqt, mrt;
 	void *csum_start = NULL;
 	__sum16 *csum = NULL;
 	struct sk_buff *skb;
 	struct igmphdr *ih;
 	struct ethhdr *eth;
-	unsigned long lmqt;
 	struct iphdr *iph;
 	u16 lmqt_srcs = 0;
 
@@ -1004,15 +1004,15 @@ static struct sk_buff *br_ip4_multicast_alloc_query(struct net_bridge_mcast *brm
 	skb_put(skb, 24);
 
 	skb_set_transport_header(skb, skb->len);
+	mrt = group ? brmctx->multicast_last_member_interval :
+		      brmctx->multicast_query_response_interval;
 	*igmp_type = IGMP_HOST_MEMBERSHIP_QUERY;
 
 	switch (brmctx->multicast_igmp_version) {
 	case 2:
 		ih = igmp_hdr(skb);
 		ih->type = IGMP_HOST_MEMBERSHIP_QUERY;
-		ih->code = (group ? brmctx->multicast_last_member_interval :
-				    brmctx->multicast_query_response_interval) /
-			   (HZ / IGMP_TIMER_SCALE);
+		ih->code = mrt / (HZ / IGMP_TIMER_SCALE);
 		ih->group = group;
 		ih->csum = 0;
 		csum = &ih->csum;
@@ -1021,11 +1021,9 @@ static struct sk_buff *br_ip4_multicast_alloc_query(struct net_bridge_mcast *brm
 	case 3:
 		ihv3 = igmpv3_query_hdr(skb);
 		ihv3->type = IGMP_HOST_MEMBERSHIP_QUERY;
-		ihv3->code = (group ? brmctx->multicast_last_member_interval :
-				      brmctx->multicast_query_response_interval) /
-			     (HZ / IGMP_TIMER_SCALE);
+		ihv3->code = igmpv3_mrc(mrt / (HZ / IGMP_TIMER_SCALE));
 		ihv3->group = group;
-		ihv3->qqic = brmctx->multicast_query_interval / HZ;
+		ihv3->qqic = igmpv3_qqic(brmctx->multicast_query_interval / HZ);
 		ihv3->nsrcs = htons(lmqt_srcs);
 		ihv3->resv = 0;
 		ihv3->suppress = sflag;
-- 
2.43.0

In MLD, QQIC and MRC fields are not currently encoded when
generating query packets. Since the receiver of the query
interprets these fields using the MLDv2 floating-point
decoding logic, any raw interval value that exceeds the
linear threshold is currently parsed incorrectly as an
exponential value, leading to an incorrect interval
calculation.

Encode and assign the corresponding protocol fields during
query generation. Introduce the logic to dynamically
calculate the exponent and mantissa using bit-scan (fls).
This ensures QQIC (8-bit) and MRC (16-bit) fields are
properly encoded when transmitting query packets with
intervals that exceed their respective linear thresholds
(128 for QQI; 32768 for MRD).

RFC3810: If QQIC >= 128, the QQIC field represents a
floating-point value as follows:
     0 1 2 3 4 5 6 7
    +-+-+-+-+-+-+-+-+
    |1| exp | mant  |
    +-+-+-+-+-+-+-+-+

RFC3810: If Maximum Response Code >= 32768, the Maximum
Response Code field represents a floating-point value as
follows:
     0 1 2 3 4 5 6 7 8 9 A B C D E F
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |1| exp |          mant         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Signed-off-by: Ujjal Roy <royujjal@gmail.com>
---
 include/net/mld.h         | 117 ++++++++++++++++++++++++++++++++++++++
 net/bridge/br_multicast.c |   4 +-
 2 files changed, 119 insertions(+), 2 deletions(-)

diff --git a/include/net/mld.h b/include/net/mld.h
index 5e093f9c75d9..1ee7d3f68a33 100644
--- a/include/net/mld.h
+++ b/include/net/mld.h
@@ -90,12 +90,129 @@ struct mld2_query {
 #define MLDV2_QQIC_MAN(value)	((value) & 0x0f)
 
 #define MLD_QQIC_MIN_THRESHOLD	128
+/* Max representable (mant = 0xF, exp = 7) -> 31744 */
+#define MLD_QQIC_MAX_THRESHOLD	31744
 #define MLD_MRC_MIN_THRESHOLD	32768UL
+/* Max representable (mant = 0xFFF, exp = 7) -> 8387584 */
+#define MLD_MRC_MAX_THRESHOLD	8387584
 #define MLDV1_MRD_MAX_COMPAT	(MLD_MRC_MIN_THRESHOLD - 1)
 
 #define MLD_MAX_QUEUE		8
 #define MLD_MAX_SKBS		32
 
+/* V2 exponential field encoding */
+
+/*
+ * Calculate Maximum Response Code from Maximum Response Delay
+ *
+ * MLDv2 Maximum Response Code 16-bit encoding (RFC3810).
+ *
+ * RFC3810 defines only the decoding formula:
+ * Maximum Response Delay = (mant | 0x1000) << (exp + 3)
+ *
+ * but does NOT define the encoding procedure. To derive exponent:
+ *
+ * For the 16-bit MRC, the "hidden bit" (0x1000) is left shifted by 12
+ * to sit above the 12-bit mantissa. The RFC then shifts this entire
+ * block left by (exp + 3) to reconstruct the value.
+ * So, 'hidden bit' is the MSB which is shifted by (12 + exp + 3).
+ *
+ * - Total left shift of the hidden bit = 12 + (exp + 3) = exp + 15.
+ * - This is the MSB at the 0-based bit position: (exp + 15).
+ * - Since fls() is 1-based, fls(value) - 1 = exp + 15.
+ *
+ * Therefore:
+ *     exp  = fls(value) - 16
+ *     mant = (value >> (exp + 3)) & 0x0FFF
+ *
+ * Final encoding formula:
+ *     0x8000 | (exp << 12) | mant
+ *
+ * Example (value = 1311744):
+ *  0               1               2               3
+ *  0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |0 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0| 1311744
+ * |                      ^-^--------mant---------^ ^...(exp+3)...^| exp=5
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *
+ * Encoded:
+ *   0x8000 | (5 << 12) | 0x404 = 0xD404
+ */
+static inline u16 mldv2_mrc(unsigned long mrd)
+{
+	u16 mc_man, mc_exp;
+
+	/* RFC3810: MRC < 32768 is literal */
+	if (mrd < MLD_MRC_MIN_THRESHOLD)
+		return (u16)mrd;
+
+	/* Saturate at max representable (mant = 0xFFF, exp = 7) -> 8387584 */
+	if (mrd >= MLD_MRC_MAX_THRESHOLD)
+		return 0xFFFF;
+
+	mc_exp = (u16)(fls(mrd) - 16);
+	mc_man = (u16)((mrd >> (mc_exp + 3)) & 0x0FFF);
+
+	return (0x8000 | (mc_exp << 12) | mc_man);
+}
+
+/*
+ * Calculate Querier's Query Interval Code from Query Interval
+ *
+ * MLDv2 QQIC 8-bit floating-point encoding (RFC3810).
+ *
+ * RFC3810 defines only the decoding formula:
+ * QQI = (mant | 0x10) << (exp + 3)
+ *
+ * but does NOT define the encoding procedure. To derive exponent:
+ *
+ * For any value of mantissa and exponent, the decoding formula
+ * indicates that the "hidden bit" (0x10) is shifted 4 bits left
+ * to sit above the 4-bit mantissa. The RFC again shifts this
+ * entire block left by (exp + 3) to reconstruct the value.
+ * So, 'hidden bit' is the MSB which is shifted by (4 + exp + 3).
+ *
+ * Total left shift of the 'hidden bit' = 4 + (exp + 3) = exp + 7.
+ * This is the MSB at the 0-based bit position: (exp + 7).
+ * Since fls() is 1-based, fls(value) - 1 = exp + 7.
+ *
+ * Therefore:
+ *     exp  = fls(value) - 8
+ *     mant = (value >> (exp + 3)) & 0x0F
+ *
+ * Final encoding formula:
+ *     0x80 | (exp << 4) | mant
+ *
+ * Example (value = 3200):
+ *  0               1
+ *  0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ * |0 0 0 0 1 1 0 0 1 0 0 0 0 0 0 0| (value = 3200)
+ * |        ^-^-mant^ ^..(exp+3)..^| exp = 4, mant = 9
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ *
+ * Encoded:
+ *   0x80 | (4 << 4) | 9 = 0xC9
+ */
+static inline u8 mldv2_qqic(unsigned long value)
+{
+	u8 mc_man, mc_exp;
+
+	/* RFC3810: QQIC < 128 is literal */
+	if (value < MLD_QQIC_MIN_THRESHOLD)
+		return (u8)value;
+
+	/* Saturate at max representable (mant = 0xF, exp = 7) -> 31744 */
+	if (value >= MLD_QQIC_MAX_THRESHOLD)
+		return 0xFF;
+
+	mc_exp  = (u8)(fls(value) - 8);
+	mc_man = (u8)((value >> (mc_exp + 3)) & 0x0F);
+
+	return (0x80 | (mc_exp << 4) | mc_man);
+}
+
 /* V2 exponential field decoding */
 
 /* Calculate Maximum Response Delay from Maximum Response Code
diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index 27010744d7ae..c2d144f6a86e 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -1181,7 +1181,7 @@ static struct sk_buff *br_ip6_multicast_alloc_query(struct net_bridge_mcast *brm
 		break;
 	case 2:
 		mld2q = (struct mld2_query *)icmp6_hdr(skb);
-		mld2q->mld2q_mrc = htons((u16)jiffies_to_msecs(interval));
+		mld2q->mld2q_mrc = htons((u16)jiffies_to_msecs(mldv2_mrc(interval)));
 		mld2q->mld2q_type = ICMPV6_MGM_QUERY;
 		mld2q->mld2q_code = 0;
 		mld2q->mld2q_cksum = 0;
@@ -1190,7 +1190,7 @@ static struct sk_buff *br_ip6_multicast_alloc_query(struct net_bridge_mcast *brm
 		mld2q->mld2q_suppress = sflag;
 		mld2q->mld2q_qrv = 2;
 		mld2q->mld2q_nsrcs = htons(llqt_srcs);
-		mld2q->mld2q_qqic = brmctx->multicast_query_interval / HZ;
+		mld2q->mld2q_qqic = mldv2_qqic(brmctx->multicast_query_interval / HZ);
 		mld2q->mld2q_mca = *group;
 		csum = &mld2q->mld2q_cksum;
 		csum_start = (void *)mld2q;
-- 
2.43.0

Add bridge selftests that configure IGMPv3 parameters and validate the
resulting Query packet fields for Max Resp Code (MRC) and Querier Query
Interval Code (QQIC).

This also adds helper binary to encode floating-point exponential fields.

Future extensions may cover corresponding IPv6 cases.

Signed-off-by: Ujjal Roy <royujjal@gmail.com>
---
 .../selftests/net/forwarding/.gitignore       |   2 +
 .../testing/selftests/net/forwarding/Makefile |  10 ++
 .../selftests/net/forwarding/bridge_igmp.sh   | 109 ++++++++++++++++++
 .../selftests/net/forwarding/mc_decode.c      |  38 ++++++
 .../selftests/net/forwarding/mc_encode.c      |  40 +++++++
 5 files changed, 199 insertions(+)
 create mode 100644 tools/testing/selftests/net/forwarding/mc_decode.c
 create mode 100644 tools/testing/selftests/net/forwarding/mc_encode.c

diff --git a/tools/testing/selftests/net/forwarding/.gitignore b/tools/testing/selftests/net/forwarding/.gitignore
index 418ff96c52ef..aa0c7f1afb4b 100644
--- a/tools/testing/selftests/net/forwarding/.gitignore
+++ b/tools/testing/selftests/net/forwarding/.gitignore
@@ -1,3 +1,5 @@
 # SPDX-License-Identifier: GPL-2.0-only
 forwarding.config
 ipmr
+mc_encode
+mc_decode
diff --git a/tools/testing/selftests/net/forwarding/Makefile b/tools/testing/selftests/net/forwarding/Makefile
index bbaf4d937dd8..a26da846632d 100644
--- a/tools/testing/selftests/net/forwarding/Makefile
+++ b/tools/testing/selftests/net/forwarding/Makefile
@@ -1,5 +1,15 @@
 # SPDX-License-Identifier: GPL-2.0+ OR MIT
 
+top_srcdir = ../../../../..
+
+CFLAGS += -Wall -Wl,--no-as-needed -O2 -g -I$(top_srcdir)/usr/include $(KHDR_INCLUDES)
+CFLAGS += -I$(top_srcdir)/tools/include
+
+TEST_GEN_FILES := \
+	mc_encode \
+	mc_decode \
+# end of TEST_GEN_FILES
+
 TEST_PROGS := \
 	bridge_activity_notify.sh \
 	bridge_fdb_learning_limit.sh \
diff --git a/tools/testing/selftests/net/forwarding/bridge_igmp.sh b/tools/testing/selftests/net/forwarding/bridge_igmp.sh
index d4e7dd659354..9841c4e4eca0 100755
--- a/tools/testing/selftests/net/forwarding/bridge_igmp.sh
+++ b/tools/testing/selftests/net/forwarding/bridge_igmp.sh
@@ -2,6 +2,8 @@
 # SPDX-License-Identifier: GPL-2.0
 
 ALL_TESTS="
+	v3query_mrc_test
+	v3query_qqic_test
 	v2reportleave_test
 	v3include_test
 	v3inc_allow_test
@@ -84,6 +86,7 @@ switch_destroy()
 {
 	ip link set dev $swp2 down
 	ip link set dev $swp1 down
+	ip link set dev br0 down
 
 	ip link del dev br0
 }
@@ -116,6 +119,112 @@ cleanup()
 	vrf_cleanup
 }
 
+check_binary()
+{
+	local cmd=$1; shift
+	local args=$@
+
+	if [[ ! -x "$(command -v "$cmd")" ]]; then
+		log_test_skip "$args $cmd not found"
+		return $EXIT_STATUS
+	fi
+}
+
+tcpdump_show_with_filter()
+{
+	local if_name=$1; shift
+	local filter=$@
+
+	tcpdump -e -n -r ${capfile[$if_name]} "$filter" 2>&1
+}
+
+validate_query()
+{
+	local if_name=$1; shift
+	local test="$1"; shift
+	local value="$1"; shift
+	local pattern=""
+	local field_val=""
+	local pos=""
+	local msg="IGMPv3 query: verify $test"
+	check_command tshark || return 1
+	check_binary "./mc_encode" $msg || return 1
+
+	if [ "$test" = "MRC" ]; then
+		pos=1 # MRC field offset within IGMP header
+		field_val=$(tshark -r ${capfile[$if_name]} -Y "igmp.type==0x11" \
+			   -V 2>/dev/null | grep "Max Resp Time")
+	elif [ "$test" = "QQIC" ]; then
+		pos=9 # QQIC field offset within IGMP header
+		field_val=$(tshark -r ${capfile[$if_name]} -Y "igmp.type==0x11" \
+			   -V 2>/dev/null | grep "QQIC")
+	fi
+
+	local enc_val=$(./mc_encode $value)
+	pattern="ip proto 2 and igmp[0] == 0x11 and igmp[$pos] == $enc_val"
+	local opt_str=""
+	tcpdump_show_with_filter $if_name $pattern | grep -q "igmp query v3"
+	ret=$?
+	if [ "$field_val" != "" -a $ret -ne 0 ]; then
+		opt_str="Bad $test value in IGMP packet: $field_val"
+	fi
+	check_err $ret "$opt_str"
+
+	log_test "$msg" "configured=$value, expected=$enc_val"
+}
+
+v3query_mrc_test()
+{
+	RET=0
+	local qri_val=160
+	local br_qri=$((qri_val*10))
+
+	# Set MRT to validate
+	ip link set dev br0 type bridge mcast_query_interval 12500 \
+					mcast_query_response_interval $br_qri \
+					mcast_igmp_version 3
+	check_err $? "IGMPv3 QUERY bridge configuration failed"
+
+	ip link set dev br0 down
+	tcpdump_start $h2
+	ip link set dev br0 up
+	sleep 2
+	tcpdump_stop $h2
+
+	validate_query $h2 "MRC" $qri_val
+	tcpdump_cleanup $h2
+
+	ip link set dev br0 type bridge mcast_query_interval 12500 \
+					mcast_query_response_interval 1000 \
+					mcast_igmp_version 2
+}
+
+v3query_qqic_test()
+{
+	RET=0
+	local qqi_val=160
+	local br_qqi=$((qqi_val*100))
+
+	# Set QQIC to validate
+	ip link set dev br0 type bridge mcast_query_interval $br_qqi \
+					mcast_query_response_interval 1000 \
+					mcast_igmp_version 3
+	check_err $? "IGMPv3 QUERY bridge configuration failed"
+
+	ip link set dev br0 down
+	tcpdump_start $h2
+	ip link set dev br0 up
+	sleep 2
+	tcpdump_stop $h2
+
+	validate_query $h2 "QQIC" $qqi_val
+	tcpdump_cleanup $h2
+
+	ip link set dev br0 type bridge mcast_query_interval 12500 \
+					mcast_query_response_interval 1000 \
+					mcast_igmp_version 2
+}
+
 v2reportleave_test()
 {
 	RET=0
diff --git a/tools/testing/selftests/net/forwarding/mc_decode.c b/tools/testing/selftests/net/forwarding/mc_decode.c
new file mode 100644
index 000000000000..5b626101497d
--- /dev/null
+++ b/tools/testing/selftests/net/forwarding/mc_decode.c
@@ -0,0 +1,38 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <stdio.h>
+#include <stdlib.h>
+#include <linux/bitops.h>
+
+#define IGMPV3_FP_EXP(value)            (((value) >> 4) & 0x07)
+#define IGMPV3_FP_MAN(value)            ((value) & 0x0f)
+
+/* IGMPV3 floating-point exponential field threshold */
+#define IGMPV3_EXP_MIN_THRESHOLD        128
+
+static inline unsigned long decode_field(const u8 code)
+{
+    /* RFC3376, relevant sections:
+     *  - 4.1.1. Maximum Response Code
+     *  - 4.1.7. QQIC (Querier's Query Interval Code)
+     */
+    if (code < IGMPV3_EXP_MIN_THRESHOLD) {
+        return (unsigned long)code;
+    } else {
+        unsigned long mc_man, mc_exp;
+        mc_exp = IGMPV3_FP_EXP(code);
+        mc_man = IGMPV3_FP_MAN(code);
+        return ((mc_man | 0x10) << (mc_exp + 3));
+    }
+}
+
+int main(int argc, char *argv[])
+{
+    uint8_t qqic = 0;
+    if (argc >= 2)
+        qqic = atoi(argv[1]);
+    unsigned long qqi = decode_field(qqic);
+
+    printf("%lu\n", qqi);
+
+    return 0;
+}
diff --git a/tools/testing/selftests/net/forwarding/mc_encode.c b/tools/testing/selftests/net/forwarding/mc_encode.c
new file mode 100644
index 000000000000..a2183b864be4
--- /dev/null
+++ b/tools/testing/selftests/net/forwarding/mc_encode.c
@@ -0,0 +1,40 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <stdio.h>
+#include <stdlib.h>
+#include <linux/bitops.h>
+
+/* IGMPV3 floating-point exponential field threshold */
+#define IGMPV3_EXP_MIN_THRESHOLD        128
+/* Max representable (mant = 0xF, exp = 7) -> 31744 */
+#define IGMPV3_EXP_MAX_THRESHOLD        31744
+
+static inline uint8_t encode_field(unsigned int value)
+{
+    uint8_t mc_exp, mc_man;
+
+    /* RFC3376: QQIC/MRC < 128 is literal */
+    if (value < IGMPV3_EXP_MIN_THRESHOLD)
+        return (uint8_t)value;
+
+    /* Saturate at max representable (mant = 0xF, exp = 7) -> 31744 */
+    if (value >= IGMPV3_EXP_MAX_THRESHOLD)
+        return 0xFF;
+
+    mc_exp  = (uint8_t)(fls(value) - 8);
+    mc_man = (uint8_t)((value >> (mc_exp + 3)) & 0x0F);
+
+    return 0x80 | (mc_exp << 4) | mc_man;
+}
+
+int main(int argc, char *argv[])
+{
+    unsigned int qqi = 0;
+    if (argc >= 2)
+        qqi = atoi(argv[1]);
+
+    uint8_t qqic = encode_field(qqi);
+
+    printf("%u\n", qqic);
+
+    return 0;
+}
-- 
2.43.0