pcnet: Properly handle TX requests during Link Fail

As long as we have no link and we aren't in internal loopback mode, no
packet must be sent. Instead, LCAR needs to be set in any active TX
descriptor and also CERR in CSR0.
Signed-off-by: NJan Kiszka <jan.kiszka@siemens.com>

hw/pcnet.c

@@ -77,6 +77,7 @@ struct qemu_ether_header {
 #define CSR_DTX(S)       !!(((S)->csr[15])&0x0002)
 #define CSR_LOOP(S)      !!(((S)->csr[15])&0x0004)
 #define CSR_DXMTFCS(S)   !!(((S)->csr[15])&0x0008)
+#define CSR_INTL(S)      !!(((S)->csr[15])&0x0040)
 #define CSR_DRCVPA(S)    !!(((S)->csr[15])&0x2000)
 #define CSR_DRCVBC(S)    !!(((S)->csr[15])&0x4000)
 #define CSR_PROM(S)      !!(((S)->csr[15])&0x8000)
@@ -1234,6 +1235,15 @@ static void pcnet_transmit(PCNetState *s)
             if (BCR_SWSTYLE(s) != 1)
                 add_crc = GET_FIELD(tmd.status, TMDS, ADDFCS);
         }
+        if (s->lnkst == 0 &&
+            (!CSR_LOOP(s) || (!CSR_INTL(s) && !BCR_TMAULOOP(s)))) {
+            SET_FIELD(&tmd.misc, TMDM, LCAR, 1);
+            SET_FIELD(&tmd.status, TMDS, ERR, 1);
+            SET_FIELD(&tmd.status, TMDS, OWN, 0);
+            s->csr[0] |= 0xa000; /* ERR | CERR */
+            s->xmit_pos = -1;
+            goto txdone;
+        }
         if (!GET_FIELD(tmd.status, TMDS, ENP)) {
             int bcnt = 4096 - GET_FIELD(tmd.length, TMDL, BCNT);
             s->phys_mem_read(s->dma_opaque, PHYSADDR(s, tmd.tbadr),
@@ -1262,6 +1272,7 @@ static void pcnet_transmit(PCNetState *s)
             s->xmit_pos = -1;
         }
 
+    txdone:
         SET_FIELD(&tmd.status, TMDS, OWN, 0);
         TMDSTORE(&tmd, PHYSADDR(s,CSR_CXDA(s)));
         if (!CSR_TOKINTD(s) || (CSR_LTINTEN(s) && GET_FIELD(tmd.status, TMDS, LTINT)))

hw/pcnet.h

@@ -20,6 +20,7 @@
 #define BCR_SWS      20
 #define BCR_PLAT     22
 
+#define BCR_TMAULOOP(S)  !!((S)->bcr[BCR_MC  ] & 0x4000)
 #define BCR_APROMWE(S)   !!((S)->bcr[BCR_MC  ] & 0x0100)
 #define BCR_DWIO(S)      !!((S)->bcr[BCR_BSBC] & 0x0080)
 #define BCR_SSIZE32(S)   !!((S)->bcr[BCR_SWS ] & 0x0100)