e1000: Fix RX descriptor low threshold interrupt logic (Alex Williamson)

The RXDMT0 interrupt is supposed to fire when the number of free
RX descriptors drops to some fraction of the total descriptors.
However in practice, it seems like we're adding this interrupt
cause on every RX.  Fix the logic to treat (tail - head) as the
number of free entries rather than the number of used entries.

Signed-off-by: Alex Williamson <alex.williamson@hp.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
git-svn-id: svn://svn.savannah.nongnu.org/qemu/branches/stable_0_10_0@6867 c046a42c-6fe2-441c-8c8c-71466251a162

diff --git a/hw/e1000.c b/hw/e1000.c
index e6155d6a6909d97f33eb48c3cf89a43b15f1c350..1644201d6ee6625e909a5f509a5cb40af0c3930b 100644 (file)
--- a/hw/e1000.c
+++ b/hw/e1000.c
@@ -666,8 +666,8 @@ e1000_receive(void *opaque, const uint8_t *buf, int size)
     n = E1000_ICS_RXT0;
     if ((rdt = s->mac_reg[RDT]) < s->mac_reg[RDH])
         rdt += s->mac_reg[RDLEN] / sizeof(desc);
-    if (((rdt - s->mac_reg[RDH]) * sizeof(desc)) << s->rxbuf_min_shift >=
-        s->mac_reg[RDLEN])
+    if (((rdt - s->mac_reg[RDH]) * sizeof(desc)) <= s->mac_reg[RDLEN] >>
+        s->rxbuf_min_shift)
         n |= E1000_ICS_RXDMT0;
 
     set_ics(s, 0, n);