dbdma: set FLUSH bit upon reception of flush command for unassigned DBDMA channels

This fixes MacOS 9 whereby it continually flushes and polls the status bits
until they are set to indicate a successful flush.
Signed-off-by: NMark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Acked-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: NDavid Gibson <david@gibson.dropbear.id.au>

hw/misc/macio/mac_dbdma.c

@@ -783,8 +783,18 @@ static void dbdma_unassigned_rw(DBDMA_io *io)
 static void dbdma_unassigned_flush(DBDMA_io *io)
 {
     DBDMA_channel *ch = io->channel;
+    dbdma_cmd *current = &ch->current;
+    uint16_t cmd;
     qemu_log_mask(LOG_GUEST_ERROR, "%s: use of unassigned channel %d\n",
                   __func__, ch->channel);
+
+    cmd = le16_to_cpu(current->command) & COMMAND_MASK;
+    if (cmd == OUTPUT_MORE || cmd == OUTPUT_LAST ||
+        cmd == INPUT_MORE || cmd == INPUT_LAST) {
+        current->xfer_status = cpu_to_le16(ch->regs[DBDMA_STATUS] | FLUSH);
+        current->res_count = cpu_to_le16(io->len);
+        dbdma_cmdptr_save(ch);
+    }
 }
 
 void* DBDMA_init (MemoryRegion **dbdma_mem)