From 119b0e0351bcdb7833f368781e6241ff283b49e5 Mon Sep 17 00:00:00 2001 From: Stefan Assmann Date: Tue, 7 Aug 2012 00:45:57 -0700 Subject: [PATCH] igb: add delay to allow igb loopback test to succeed on 8086:10c9 Some 8086:10c9 NICs have a problem completing the ethtool loopback test. The result looks like this: ethtool -t eth1 The test result is FAIL The test extra info: Register test (offline) 0 Eeprom test (offline) 0 Interrupt test (offline) 0 Loopback test (offline) 13 Link test (on/offline) 0 A bisect clearly points to commit a95a07445ee97a2fef65befafbadcc30ca1bd145. However that seems to only trigger the bug. While adding some printk the problem disappeared, so this might be a timing issue. After some trial and error I discovered that adding a small delay just before igb_write_phy_reg() in igb_integrated_phy_loopback() allows the loopback test to succeed. I was unable to figure out the root cause so far but I expect it to be somewhere in the following executing path igb_integrated_phy_loopback ->igb_write_phy_reg_igp ->igb_write_phy_reg_mdic ->igb_acquire_phy_82575 ->igb_acquire_swfw_sync_82575 The problem could only be observed on 8086:10c9 NICs so far and not all of them show the behaviour. I did not restrict the workaround to this type of NIC as it should do no harm to other igb NICs. With the patch below the loopback test succeeded 500 times in a row using a NIC that would otherwise fail. Signed-off-by: Stefan Assmann Tested-by: Aaron Brown Signed-off-by: Peter P Waskiewicz Jr --- drivers/net/ethernet/intel/igb/igb_ethtool.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/drivers/net/ethernet/intel/igb/igb_ethtool.c b/drivers/net/ethernet/intel/igb/igb_ethtool.c index 90550f5e3dd9..70591117051b 100644 --- a/drivers/net/ethernet/intel/igb/igb_ethtool.c +++ b/drivers/net/ethernet/intel/igb/igb_ethtool.c @@ -1498,6 +1498,9 @@ static int igb_integrated_phy_loopback(struct igb_adapter *adapter) break; } + /* add small delay to avoid loopback test failure */ + msleep(50); + /* force 1000, set loopback */ igb_write_phy_reg(hw, PHY_CONTROL, 0x4140); -- 2.20.1