hw/net/eepro100: Implement read-only bits in MDI registers

Although we defined an eepro100_mdi_mask[] array indicating which bits
in the registers are read-only, we weren't actually doing anything with
it. Make the MDI register-write code use it rather than manually making
register 1 read-only and leaving the rest as reads-as-written. (The
special-case handling of register 0 remains as before since its mask is
all-zeros and the special casing happens before we apply the masking.)
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Message-id: 1402159924-13853-1-git-send-email-peter.maydell@linaro.org
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

hw/net/eepro100.c

@@ -1217,7 +1217,6 @@ static void eepro100_write_mdi(EEPRO100State *s)
                 break;
             case 1:            /* Status Register */
                 missing("not writable");
-                data = s->mdimem[reg];
                 break;
             case 2:            /* PHY Identification Register (Word 1) */
             case 3:            /* PHY Identification Register (Word 2) */
@@ -1230,7 +1229,8 @@ static void eepro100_write_mdi(EEPRO100State *s)
             default:
                 missing("not implemented");
             }
-            s->mdimem[reg] = data;
+            s->mdimem[reg] &= eepro100_mdi_mask[reg];
+            s->mdimem[reg] |= data & ~eepro100_mdi_mask[reg];
         } else if (opcode == 2) {
             /* MDI read */
             switch (reg) {