--- zzzz-none-000/linux-3.10.107/include/net/mld.h	2017-06-27 09:49:32.000000000 +0000
+++ vr9-7490-729/linux-3.10.107/include/net/mld.h	2021-11-10 11:53:56.000000000 +0000
@@ -72,4 +72,55 @@
 
 #define MLDV2_MRC(value) MLDV2_EXP(0x8000, 12, 3, value)
 
+/* AVM: backport from v3.15
+ *
+ * commits:
+ * 89225d1ce6af3916bf32aecbe9d83f571a098588 net: ipv6: mld: fix v1/v2 switchback timeout to rfc3810, 9.12.
+ * e3f5b17047dec4acd8957dad053e70d87f18d97e net: ipv6: mld: get rid of MLDV2_MRC and simplify calculation
+ */
+/* RFC3810, 5.1.3. Maximum Response Code:
+ *
+ * If Maximum Response Code >= 32768, Maximum Response Code 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         |
+ * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ */
+#define MLDV2_MRC_EXP(value)	(((value) >> 12) & 0x0007)
+#define MLDV2_MRC_MAN(value)	((value) & 0x0fff)
+
+/* RFC3810, 5.1.9. QQIC (Querier's Query Interval Code):
+ *
+ * If QQIC >= 128, QQIC represents a floating-point value as follows:
+ *
+ *  0 1 2 3 4 5 6 7
+ * +-+-+-+-+-+-+-+-+
+ * |1| exp | mant  |
+ * +-+-+-+-+-+-+-+-+
+ */
+#define MLDV2_QQIC_EXP(value)	(((value) >> 4) & 0x07)
+#define MLDV2_QQIC_MAN(value)	((value) & 0x0f)
+
+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);
+
+       if (mc_mrc < 32768) {
+               ret = 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 ret;
+}
+
+
 #endif