FEC: Remove endless loop in the FEC driver

The FEC hardware sometimes errors out on data transfer and hangs in
the tightloop adjusted by this patch. So add timeout into the tightloop
to make such a hang recoverable.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Joe Hershberger <joe.hershberger@ni.com>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: Otavio Salvador <otavio@ossystems.com.br>
Cc: Stefano Babic <sbabic@denx.de>

drivers/net/fec_mxc.c

@@ -35,6 +35,12 @@
 
 DECLARE_GLOBAL_DATA_PTR;
 
+/*
+ * Timeout the transfer after 5 mS. This is usually a bit more, since
+ * the code in the tightloops this timeout is used in adds some overhead.
+ */
+#define FEC_XFER_TIMEOUT	5000
+
 #ifndef CONFIG_MII
 #error "CONFIG_MII has to be defined!"
 #endif
@@ -697,6 +703,8 @@ static int fec_send(struct eth_device *dev, void *packet, int length)
 	unsigned int status;
 	uint32_t size, end;
 	uint32_t addr;
+	int timeout = FEC_XFER_TIMEOUT;
+	int ret = 0;
 
 	/*
 	 * This routine transmits one frame.  This routine only accepts
@@ -764,6 +772,10 @@ static int fec_send(struct eth_device *dev, void *packet, int length)
 	while (readw(&fec->tbd_base[fec->tbd_index].status) & FEC_TBD_READY) {
 		udelay(1);
 		invalidate_dcache_range(addr, addr + size);
+		if (!timeout--) {
+			ret = -EINVAL;
+			break;
+		}
 	}
 
 	debug("fec_send: status 0x%x index %d\n",
@@ -775,7 +787,7 @@ static int fec_send(struct eth_device *dev, void *packet, int length)
 	else
 		fec->tbd_index = 1;
 
-	return 0;
+	return ret;
 }
 
 /**