[Qemu-devel] [RFC PATCH 1/2] e1000: Use Address_Available bit as HW latch

[Vlad Yasevich <vyasevic@redhat.com>]

e1000 provides a E1000_RAH_AV bit on every complete write
to the Receive Address Register.  We can use this bit
2 ways:
 1) To trigger HMP notifications.  When the bit is set the
    mac address is fully set and we can update the HMP.

 2) We can turn off he bit on the write to low order bits of
    the Receive Address Register, so that we would not try
    to match received traffic to this address when it is
    not completely set.

Signed-off-by: Vlad Yasevich <vyasevic@redhat.com>
---
 hw/net/e1000.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/hw/net/e1000.c b/hw/net/e1000.c
index ae63591..82978ea 100644
--- a/hw/net/e1000.c
+++ b/hw/net/e1000.c
@@ -1106,10 +1106,19 @@ mac_writereg(E1000State *s, int index, uint32_t val)
 
     s->mac_reg[index] = val;
 
-    if (index == RA || index == RA + 1) {
+    switch (index) {
+    case RA:
+        /* Mask off AV bit on the write of the low dword.  The write of
+         * the high dword will set the bit.  This way a half-written
+         * mac address will not be used to filter on rx.
+         */
+        s->mac_reg[RA+1] &= ~E1000_RAH_AV;
+        break;
+    case (RA + 1):
         macaddr[0] = cpu_to_le32(s->mac_reg[RA]);
         macaddr[1] = cpu_to_le32(s->mac_reg[RA + 1]);
         qemu_format_nic_info_str(qemu_get_queue(s->nic), (uint8_t *)macaddr);
+        break;
     }
 }
 
-- 
1.8.4.2