netdev - Re: [E1000-devel] [PATCH net-next] igb: add delay to allow igb loopback test to succeed on 8086:10c9

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Date:	Wed, 01 Aug 2012 18:06:49 -0700
From:	Jeff Kirsher <jeffrey.t.kirsher@...el.com>
To:	Stefan Assmann <sassmann@...nic.de>
Cc:	netdev@...r.kernel.org, e1000-devel@...ts.sourceforge.net
Subject: Re: [E1000-devel] [PATCH net-next] igb: add delay to allow igb
 loopback test to succeed on 8086:10c9

On Wed, 2012-08-01 at 13:44 +0200, Stefan Assmann wrote:
> 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
> 
> As this workaround only introduces a minor delay, which is not in the
> hot
> path I hope this is acceptable. The problem could only be oberved 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 <sassmann@...nic.de>
> ---
>  drivers/net/ethernet/intel/igb/igb_ethtool.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-) 

Thanks Stefan, I have added the patch to my queue.

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