rtl8139: support byte read to TxStatus registers

Some drivers (such as win7) use byte read for TxStatus registers, so we need to
support this to let guest driver behave correctly.

For writing, only double-word access is allowed by spec.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/rtl8139.c

@@ -2495,11 +2495,30 @@ static void rtl8139_TxStatus_write(RTL8139State *s, uint32_t txRegOffset, uint32
     rtl8139_transmit(s);
 }
 
-static uint32_t rtl8139_TxStatus_read(RTL8139State *s, uint32_t txRegOffset)
+static uint32_t rtl8139_TxStatus_read(RTL8139State *s, uint8_t addr, int size)
 {
-    uint32_t ret = s->TxStatus[txRegOffset/4];
+    uint32_t reg = (addr - TxStatus0) / 4;
+    uint32_t offset = addr & 0x3;
+    uint32_t ret = 0;
+
+    if (addr & (size - 1)) {
+        DPRINTF("not implemented read for TxStatus addr=0x%x size=0x%x\n", addr,
+                size);
+        return ret;
+    }
 
-    DPRINTF("TxStatus read offset=0x%x val=0x%08x\n", txRegOffset, ret);
+    switch (size) {
+    case 1: /* fall through */
+    case 2: /* fall through */
+    case 4:
+        ret = (s->TxStatus[reg] >> offset * 8) & ((1 << (size * 8)) - 1);
+        DPRINTF("TxStatus[%d] read addr=0x%x size=0x%x val=0x%08x\n", reg, addr,
+                size, ret);
+        break;
+    default:
+        DPRINTF("unsupported size 0x%x of TxStatus reading\n", size);
+        break;
+    }
 
     return ret;
 }
@@ -2970,6 +2989,9 @@ static uint32_t rtl8139_io_readb(void *opaque, uint8_t addr)
         case MAR0 ... MAR0+7:
             ret = s->mult[addr - MAR0];
             break;
+        case TxStatus0 ... TxStatus0+4*4-1:
+            ret = rtl8139_TxStatus_read(s, addr, 1);
+            break;
         case ChipCmd:
             ret = rtl8139_ChipCmd_read(s);
             break;
@@ -3033,6 +3055,9 @@ static uint32_t rtl8139_io_readw(void *opaque, uint8_t addr)
 
     switch (addr)
     {
+        case TxAddr0 ... TxAddr0+4*4-1:
+            ret = rtl8139_TxStatus_read(s, addr, 2);
+            break;
         case IntrMask:
             ret = rtl8139_IntrMask_read(s);
             break;
@@ -3123,7 +3148,7 @@ static uint32_t rtl8139_io_readl(void *opaque, uint8_t addr)
             break;
 
         case TxStatus0 ... TxStatus0+4*4-1:
-            ret = rtl8139_TxStatus_read(s, addr-TxStatus0);
+            ret = rtl8139_TxStatus_read(s, addr, 4);
             break;
 
         case TxAddr0 ... TxAddr0+4*4-1: