Cadence: gem: fix wraparound in 64bit descriptors

Wraparound of TX descriptor cyclic buffer only updated
the low 32 bits of the descriptor.
Fix that by checking if we're working with 64bit descriptors.
Signed-off-by: NRamon Fried <rfried.dev@gmail.com>
Reviewed-by: NEdgar E. Iglesias <edgar.iglesias@xilinx.com>
Message-id: 20200417171736.441607-1-rfried.dev@gmail.com
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

hw/net/cadence_gem.c

@@ -1238,7 +1238,14 @@ static void gem_transmit(CadenceGEMState *s)
             /* read next descriptor */
             if (tx_desc_get_wrap(desc)) {
                 tx_desc_set_last(desc);
-                packet_desc_addr = s->regs[GEM_TXQBASE];
+
+                if (s->regs[GEM_DMACFG] & GEM_DMACFG_ADDR_64B) {
+                    packet_desc_addr = s->regs[GEM_TBQPH];
+                    packet_desc_addr <<= 32;
+                } else {
+                    packet_desc_addr = 0;
+                }
+                packet_desc_addr |= s->regs[GEM_TXQBASE];
             } else {
                 packet_desc_addr += 4 * gem_get_desc_len(s, false);
             }