[PATCH 1/1] igb: Report speed and duplex as unknown when device is runtime suspended

[Kai-Heng Feng]

BugLink: https://bugs.launchpad.net/bugs/1880656

igb device gets runtime suspended when there's no link partner. We can't
get correct speed under that state:
$ cat /sys/class/net/enp3s0/speed
1000

In addition to that, an error can also be spotted in dmesg:
[  385.991957] igb 0000:03:00.0 enp3s0: PCIe link lost

Since device can only be runtime suspended when there's no link partner,
we can skip reading register and let the following logic set speed and
duplex with correct status.

The more generic approach will be wrap get_link_ksettings() with begin()
and complete() callbacks. However, for this particular issue, begin()
calls igb_runtime_resume() , which tries to rtnl_lock() while the lock
is already hold by upper ethtool layer.

So let's take this approach until the igb_runtime_resume() no longer
needs to hold rtnl_lock.

CC: stable <stable at vger.kernel.org>
Suggested-by: Alexander Duyck <alexander.duyck at gmail.com>
Signed-off-by: Kai-Heng Feng <kai.heng.feng at canonical.com>
Tested-by: Aaron Brown <aaron.f.brown at intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher at intel.com>
(cherry picked from commit 165ae7a8feb53dc47fb041357e4b253bfc927cf9 linux-next)
Signed-off-by: Kai-Heng Feng <kai.heng.feng at canonical.com>
---
 drivers/net/ethernet/intel/igb/igb_ethtool.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/intel/igb/igb_ethtool.c b/drivers/net/ethernet/intel/igb/igb_ethtool.c
index 39d3b76a6f5d..2cd003c5ad43 100644
--- a/drivers/net/ethernet/intel/igb/igb_ethtool.c
+++ b/drivers/net/ethernet/intel/igb/igb_ethtool.c
@@ -143,7 +143,8 @@ static int igb_get_link_ksettings(struct net_device *netdev,
 	u32 speed;
 	u32 supported, advertising;
 
-	status = rd32(E1000_STATUS);
+	status = pm_runtime_suspended(&adapter->pdev->dev) ?
+		 0 : rd32(E1000_STATUS);
 	if (hw->phy.media_type == e1000_media_type_copper) {
 
 		supported = (SUPPORTED_10baseT_Half |
-- 
2.17.1