[PATCH v3] net/imx_fec: Adding support for MAC filtering in the FEC IP implementation.

[bilalwasim676@gmail.com]

From: bwasim <bilalwasim676@gmail.com>

This addition ensures that the IP does NOT boot up in promiscuous mode
by default, and so the software only receives the desired
packets(Unicast, Broadcast, Unicast / Multicast hashed) by default.
The software running on-top of QEMU can also modify these settings and
disable reception of broadcast frames or make the IP receive all packets (PROM mode).
This patch greatly reduces the number of packets received by the
software running on-top of the QEMU model. Tested with the armv7-a SABRE_LITE machine.
Testing included running a custom OS with IPv4 / IPv6 support. Hashing
and filtering of packets is tested to work well. Skeleton taken from
the CADENCE_GEM IP and hash generation algorithm from the Linux Kernel.

Signed-off-by: Bilal Wasim <bilalwasim676@gmail.com>
---
 hw/net/imx_fec.c         | 109 ++++++++++++++++++++++++++++++++++++++-
 include/hw/net/imx_fec.h |  10 ++++
 2 files changed, 118 insertions(+), 1 deletion(-)

diff --git a/hw/net/imx_fec.c b/hw/net/imx_fec.c
index bd99236864..d248f39fb0 100644
--- a/hw/net/imx_fec.c
+++ b/hw/net/imx_fec.c
@@ -419,6 +419,79 @@ static void imx_enet_write_bd(IMXENETBufDesc *bd, dma_addr_t addr)
     dma_memory_write(&address_space_memory, addr, bd, sizeof(*bd));
 }
 
+/*
+ * Calculate a FEC MAC Address hash index
+ */
+static unsigned calc_mac_hash(const uint8_t *mac, uint8_t mac_length)
+{
+    uint32_t crc = net_crc32_le(mac, mac_length);
+
+    /*
+     * only upper 6 bits (FEC_HASH_BITS) are used
+     * which point to specific bit in the hash registers
+     */
+    return (crc >> (32 - FEC_HASH_BITS)) & 0x3f;
+}
+
+/*
+ * fec_mac_address_filter:
+ * Accept or reject this destination address?
+ */
+static int fec_mac_address_filter(IMXFECState *s, const uint8_t *packet)
+{
+    const uint8_t broadcast_addr[] = { 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF };
+    uint32_t addr1, addr2;
+    uint8_t  hash;
+
+    /* Promiscuous mode? */
+    if (s->regs[ENET_RCR] & ENET_RCR_PROM) {
+        /* Accept all packets in promiscuous mode (even if bc_rej is set). */
+        return FEC_RX_PROMISCUOUS_ACCEPT;
+    }
+
+    /* Broadcast packet? */
+    if (!memcmp(packet, broadcast_addr, 6)) {
+        /* Reject broadcast packets? */
+        if (s->regs[ENET_RCR] & ENET_RCR_BC_REJ) {
+            return FEC_RX_REJECT;
+        }
+        /* Accept packets from broadcast address. */
+        return FEC_RX_BROADCAST_ACCEPT;
+    }
+
+    /* Accept packets -w- hash match? */
+    hash = calc_mac_hash(packet, 6);
+
+    /* Accept packets -w- multicast hash match? */
+    if ((packet[0] & 0x01) == 0x01) {
+        /* Computed hash matches GAUR / GALR register ? */
+        if (((hash < 32) && (s->regs[ENET_GALR] & (1 << hash)))
+                || ((hash > 31) && (s->regs[ENET_GAUR] & (1 << (hash - 32))))) {
+            /* Accept multicast hash enabled address. */
+            return FEC_RX_MULTICAST_HASH_ACCEPT;
+        }
+    } else {
+        /* Computed hash matches IAUR / IALR register ? */
+        if (((hash < 32) && (s->regs[ENET_IALR] & (1 << hash)))
+                || ((hash > 31) && (s->regs[ENET_IAUR] & (1 << (hash - 32))))) {
+            /* Accept multicast hash enabled address. */
+            return FEC_RX_UNICAST_HASH_ACCEPT;
+        }
+    }
+
+    /* Match Unicast address. */
+    addr1  = g_htonl(s->regs[ENET_PALR]);
+    addr2  = g_htonl(s->regs[ENET_PAUR]);
+    if (!(memcmp(packet, (uint8_t *) &addr1, 4) ||
+          memcmp(packet + 4, (uint8_t *) &addr2, 2))) {
+        /* Accept packet because it matches my unicast address. */
+        return FEC_RX_UNICAST_ACCEPT;
+    }
+
+    /* Return -1 because we do NOT support MAC address filtering.. */
+    return FEC_RX_REJECT;
+}
+
 static void imx_eth_update(IMXFECState *s)
 {
     /*
@@ -984,7 +1057,7 @@ static void imx_eth_write(void *opaque, hwaddr offset, uint64_t value,
     case ENET_IALR:
     case ENET_GAUR:
     case ENET_GALR:
-        /* TODO: implement MAC hash filtering.  */
+        s->regs[index] |= value;
         break;
     case ENET_TFWR:
         if (s->is_fec) {
@@ -1066,8 +1139,15 @@ static ssize_t imx_fec_receive(NetClientState *nc, const uint8_t *buf,
     uint32_t buf_addr;
     uint8_t *crc_ptr;
     unsigned int buf_len;
+    int maf;
     size_t size = len;
 
+    /* Is this destination MAC address "for us" ? */
+    maf = fec_mac_address_filter(s, buf);
+    if (maf == FEC_RX_REJECT) {
+        return FEC_RX_REJECT;
+    }
+
     FEC_PRINTF("len %d\n", (int)size);
 
     if (!s->regs[ENET_RDAR]) {
@@ -1133,6 +1213,16 @@ static ssize_t imx_fec_receive(NetClientState *nc, const uint8_t *buf,
         } else {
             s->regs[ENET_EIR] |= ENET_INT_RXB;
         }
+
+        /* Update descriptor based on the "maf" flag. */
+        if (maf == FEC_RX_BROADCAST_ACCEPT) {
+            /* The packet is destined for the "broadcast" address. */
+            bd.flags |= ENET_BD_BC;
+        } else if (maf == FEC_RX_MULTICAST_HASH_ACCEPT) {
+            /* The packet is destined for a "multicast" address. */
+            bd.flags |= ENET_BD_MC;
+        }
+
         imx_fec_write_bd(&bd, addr);
         /* Advance to the next descriptor.  */
         if ((bd.flags & ENET_BD_W) != 0) {
@@ -1159,8 +1249,15 @@ static ssize_t imx_enet_receive(NetClientState *nc, const uint8_t *buf,
     uint8_t *crc_ptr;
     unsigned int buf_len;
     size_t size = len;
+    int maf;
     bool shift16 = s->regs[ENET_RACC] & ENET_RACC_SHIFT16;
 
+    /* Is this destination MAC address "for us" ? */
+    maf = fec_mac_address_filter(s, buf);
+    if (maf == FEC_RX_REJECT) {
+        return FEC_RX_REJECT;
+    }
+
     FEC_PRINTF("len %d\n", (int)size);
 
     if (!s->regs[ENET_RDAR]) {
@@ -1254,6 +1351,16 @@ static ssize_t imx_enet_receive(NetClientState *nc, const uint8_t *buf,
                 s->regs[ENET_EIR] |= ENET_INT_RXB;
             }
         }
+
+        /* Update descriptor based on the "maf" flag. */
+        if (maf == FEC_RX_BROADCAST_ACCEPT) {
+            /* The packet is destined for the "broadcast" address. */
+            bd.flags |= ENET_BD_BC;
+        } else if (maf == FEC_RX_MULTICAST_HASH_ACCEPT) {
+            /* The packet is destined for a "multicast" address. */
+            bd.flags |= ENET_BD_MC;
+        }
+
         imx_enet_write_bd(&bd, addr);
         /* Advance to the next descriptor.  */
         if ((bd.flags & ENET_BD_W) != 0) {
diff --git a/include/hw/net/imx_fec.h b/include/hw/net/imx_fec.h
index 7b3faa4019..f9cfcf6af5 100644
--- a/include/hw/net/imx_fec.h
+++ b/include/hw/net/imx_fec.h
@@ -275,4 +275,14 @@ typedef struct IMXFECState {
     uint8_t frame[ENET_MAX_FRAME_SIZE];
 } IMXFECState;
 
+/* FEC address filtering defines. */
+#define FEC_RX_REJECT                   (-1)
+#define FEC_RX_PROMISCUOUS_ACCEPT       (-2)
+#define FEC_RX_BROADCAST_ACCEPT         (-3)
+#define FEC_RX_MULTICAST_HASH_ACCEPT    (-4)
+#define FEC_RX_UNICAST_HASH_ACCEPT      (-5)
+#define FEC_RX_UNICAST_ACCEPT           (-6)
+
+#define FEC_HASH_BITS                    6    /* #bits in hash */
+
 #endif
-- 
2.19.1.windows.1