From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mason Subject: Debugging Ethernet issues Date: Sun, 13 Nov 2016 01:01:14 +0100 Message-ID: <5827AD4A.7010908@free.fr> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Cc: Florian Fainelli , Mans Rullgard , Sergei Shtylyov , Tom Lendacky , Zach Brown , Andrew Lunn , Shaohui Xie , Tim Beale , Brian Hill , Vince Bridgers , Balakumaran Kannan , "David S. Miller" , Sebastian Frias , Kirill Kapranov To: netdev Return-path: Received: from smtp2-g21.free.fr ([212.27.42.2]:57042 "EHLO smtp2-g21.free.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750979AbcKMABx (ORCPT ); Sat, 12 Nov 2016 19:01:53 -0500 Sender: netdev-owner@vger.kernel.org List-ID: Hello everyone, In a past thread ("Ethernet not working on a different SoC with same eth HW") I was struggling getting Ethernet to work at all on a new board using a recent 4.7 kernel. After much hair-pulling, it turned out that *some* of the breakage was caused by a local patch which should have been guarded by a preprocessor macro. But even after reverting that patch, Ethernet does not work well on this board with kernel 4.7 whereas if I use an ancient 3.4 kernel, then Ethernet works much better. Differences: When connected to a 100 Mbps switch 3.4 negotiates a LAN DHCP setup instantly 4.7 times out When connected to a Gigabit switch 3.4 negotiates a LAN DHCP setup instantly 4.7 requires over 5 seconds to do so (In case it matters, my board is using an Atheros 8035 PHY.) I am aware that there have been hundreds of patches to the phy and net frameworks in the 3.4 to 4.7 time-frame. I'm wondering if there are important events I can log, to see what is going wrong in the 4.7 case? Are there kernel debugging options I might turn on, to better understand what is going wrong? I would be extremely grateful for any insight on this subject. Regards.