firewire: ohci: wait for local CSR lock access to finish

Add a loop to wait for the controller to finish a locally-initiated CSR
lock operation.  Google shows some occurrences of the "swap not done
yet" message which might indicate that some OHCI controllers are not
fast enough to do the lock/swap in the time needed for one PCI access.

This also correctly handles the case where the lock operation did not
finish, instead of silently returning an uninitialized value.
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

drivers/firewire/ohci.c

@@ -1158,7 +1158,7 @@ static void handle_local_lock(struct fw_ohci *ohci,
 			      struct fw_packet *packet, u32 csr)
 {
 	struct fw_packet response;
-	int tcode, length, ext_tcode, sel;
+	int tcode, length, ext_tcode, sel, try;
 	__be32 *payload, lock_old;
 	u32 lock_arg, lock_data;
 
@@ -1185,13 +1185,19 @@ static void handle_local_lock(struct fw_ohci *ohci,
 	reg_write(ohci, OHCI1394_CSRCompareData, lock_arg);
 	reg_write(ohci, OHCI1394_CSRControl, sel);
 
-	if (reg_read(ohci, OHCI1394_CSRControl) & 0x80000000)
-		lock_old = cpu_to_be32(reg_read(ohci, OHCI1394_CSRData));
-	else
-		fw_notify("swap not done yet\n");
-
+	for (try = 0; try < 20; try++)
+		if (reg_read(ohci, OHCI1394_CSRControl) & 0x80000000) {
+			lock_old = cpu_to_be32(reg_read(ohci,
+							OHCI1394_CSRData));
 			fw_fill_response(&response, packet->header,
-			 RCODE_COMPLETE, &lock_old, sizeof(lock_old));
+					 RCODE_COMPLETE,
+					 &lock_old, sizeof(lock_old));
+			goto out;
+		}
+
+	fw_error("swap not done (CSR lock timeout)\n");
+	fw_fill_response(&response, packet->header, RCODE_BUSY, NULL, 0);
+
  out:
 	fw_core_handle_response(&ohci->card, &response);
 }