[PATCH for-7.2 v3 2/3] rtl8139: keep Tx command mode 0 and 1 separate

[Stefan Hajnoczi]

There are two Tx Descriptor formats called mode 0 and mode 1. The mode
is determined by the Large Send bit.

CP_TX_IPCS (bit 18) is defined in mode 1 but the code checks the bit
unconditionally. In mode 0 bit 18 is part of the Large Send MSS value.

Explicitly check the Large Send bit to distinguish Tx command modes.
This avoids bugs where modes are confused. Note that I didn't find any
actual bugs aside from needlessly computing the IP checksum when the
Large Send bit is enabled.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 hw/net/rtl8139.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/hw/net/rtl8139.c b/hw/net/rtl8139.c
index ffef3789b5..6dd7a8e6e0 100644
--- a/hw/net/rtl8139.c
+++ b/hw/net/rtl8139.c
@@ -2135,7 +2135,7 @@ static int rtl8139_cplus_transmit_one(RTL8139State *s)
             }
             ip_data_len -= hlen;
 
-            if (txdw0 & CP_TX_IPCS)
+            if (!(txdw0 & CP_TX_LGSEN) && (txdw0 & CP_TX_IPCS))
             {
                 DPRINTF("+++ C+ mode need IP checksum\n");
 
@@ -2268,7 +2268,7 @@ static int rtl8139_cplus_transmit_one(RTL8139State *s)
                 /* Stop sending this frame */
                 saved_size = 0;
             }
-            else if (txdw0 & (CP_TX_TCPCS|CP_TX_UDPCS))
+            else if (!(txdw0 & CP_TX_LGSEN) && (txdw0 & 
(CP_TX_TCPCS|CP_TX_UDPCS)))
             {
                 DPRINTF("+++ C+ mode need TCP or UDP checksum\n");
 
-- 
2.38.1