ethtool: runtime-resume netdev parent in ethnl_ops_begin

If a network device is runtime-suspended then:
- network device may be flagged as detached and all ethtool ops (even if not
  accessing the device) will fail because netif_device_present() returns
  false
- ethtool ops may fail because device is not accessible (e.g. because being
  in D3 in case of a PCI device)

It may not be desirable that userspace can't use even simple ethtool ops
that not access the device if interface or link is down. To be more friendly
to userspace let's ensure that device is runtime-resumed when executing the
respective ethtool op in kernel.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ethtool/netlink.c

@@ -2,6 +2,7 @@
 
 #include <net/sock.h>
 #include <linux/ethtool_netlink.h>
+#include <linux/pm_runtime.h>
 #include "netlink.h"
 
 static struct genl_family ethtool_genl_family;
@@ -31,22 +32,40 @@ const struct nla_policy ethnl_header_policy_stats[] = {
 
 int ethnl_ops_begin(struct net_device *dev)
 {
+	int ret;
+
 	if (!dev)
 		return 0;
 
-	if (!netif_device_present(dev))
-		return -ENODEV;
+	if (dev->dev.parent)
+		pm_runtime_get_sync(dev->dev.parent);
 
-	if (dev->ethtool_ops->begin)
-		return dev->ethtool_ops->begin(dev);
-	else
-		return 0;
+	if (!netif_device_present(dev)) {
+		ret = -ENODEV;
+		goto err;
+	}
+
+	if (dev->ethtool_ops->begin) {
+		ret = dev->ethtool_ops->begin(dev);
+		if (ret)
+			goto err;
+	}
+
+	return 0;
+err:
+	if (dev->dev.parent)
+		pm_runtime_put(dev->dev.parent);
+
+	return ret;
 }
 
 void ethnl_ops_complete(struct net_device *dev)
 {
 	if (dev && dev->ethtool_ops->complete)
 		dev->ethtool_ops->complete(dev);
+
+	if (dev->dev.parent)
+		pm_runtime_put(dev->dev.parent);
 }
 
 /**