netpoll: Introduce netpoll_carrier_timeout kernel option

Some PHYs require longer timeouts for carrier detection, and
auto-negotiation process may take indefinite amount of time.

It may be inconvenient to force longer timeouts for sane PHYs,
so let's introduce a kernel command line option.

Since we're using module_param(), the option also can be
changed in runtime.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/kernel-parameters.txt

@@ -1531,6 +1531,11 @@ and is between 256 and 4096 characters. It is defined in the file
 			symbolic names: lapic and ioapic
 			Example: nmi_watchdog=2 or nmi_watchdog=panic,lapic
 
+	netpoll.carrier_timeout=
+			[NET] Specifies amount of time (in seconds) that
+			netpoll should wait for a carrier. By default netpoll
+			waits 4 seconds.
+
 	no387		[BUGS=X86-32] Tells the kernel to use the 387 maths
 			emulation library even if a 387 maths coprocessor
 			is present.

net/core/netpoll.c

@@ -9,6 +9,7 @@
  * Copyright (C) 2002  Red Hat, Inc.
  */
 
+#include <linux/moduleparam.h>
 #include <linux/netdevice.h>
 #include <linux/etherdevice.h>
 #include <linux/string.h>
@@ -50,6 +51,9 @@ static atomic_t trapped;
 static void zap_completion_queue(void);
 static void arp_reply(struct sk_buff *skb);
 
+static unsigned int carrier_timeout = 4;
+module_param(carrier_timeout, uint, 0644);
+
 static void queue_process(struct work_struct *work)
 {
 	struct netpoll_info *npinfo =
@@ -732,7 +736,7 @@ int netpoll_setup(struct netpoll *np)
 		}
 
 		atleast = jiffies + HZ/10;
-		atmost = jiffies + 4*HZ;
+		atmost = jiffies + carrier_timeout * HZ;
 		while (!netif_carrier_ok(ndev)) {
 			if (time_after(jiffies, atmost)) {
 				printk(KERN_NOTICE