rtl8139: keep Tx command mode 0 and 1 separate

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.

Acked-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20221117165554.1773409-3-stefanha@redhat.com>

diff --git a/hw/net/rtl8139.c b/hw/net/rtl8139.c
index ffef3789b5546b9686a08364f1ef8d36308ee838..6dd7a8e6e0747cfa109ca40bd98a63dbb95a1edd 100644 (file)
--- 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");