Date: Tue, 22 Jan 2013 23:13:46 -0800 From: Neel Natu <neelnatu@gmail.com> To: freebsd-net@freebsd.org Cc: jfv@freebsd.org Subject: e1000 serdes link flap Message-ID: <CAFgRE9EpskSJ=PHG0qhDoDE6eP1_yXTidOwnhr8q-M=G3UCHSQ@mail.gmail.com>
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Hi,
I am running into a problem in head with the e1000 link state
detection logic attached to a 82571EB serdes controller.
The symptom is that the link state keeps flapping between "up" and "down".
After I enabled the debug output in
'e1000_check_for_serdes_link_82571()' this is what I see:
<snip>
e1000_check_for_serdes_link_82571
ctrl = 0x4c0241, status = 0x803a7, rxcw = 0x44000000
FORCED_UP -> AN_PROG
em6: link state changed to DOWN
e1000_check_for_serdes_link_82571
ctrl = 0x4c0201, status = 0x803a4, rxcw = 0x44000000
AN_PROG -> FORCED_UP
em6: link state changed to UP
e1000_check_for_serdes_link_82571
ctrl = 0x4c0241, status = 0x803a7, rxcw = 0x44000000
FORCED_UP -> AN_PROG
em6: link state changed to DOWN
</snip>
The problem goes away if I apply the following patch to bring the link
state detection logic in line with the e1000e driver in Linux:
Index: e1000_82571.c
===================================================================
--- e1000_82571.c (revision 245766)
+++ e1000_82571.c (working copy)
@@ -1712,10 +1712,8 @@
* auto-negotiation in the TXCW register and disable
* forced link in the Device Control register in an
* attempt to auto-negotiate with our link partner.
- * If the partner code word is null, stop forcing
- * and restart auto negotiation.
*/
- if ((rxcw & E1000_RXCW_C) || !(rxcw & E1000_RXCW_CW)) {
+ if ((rxcw & E1000_RXCW_C) != 0) {
/* Enable autoneg, and unforce link up */
E1000_WRITE_REG(hw, E1000_TXCW, mac->txcw);
E1000_WRITE_REG(hw, E1000_CTRL,
I am not sure why the !(rxcw & E1000_RXCW_CW) check was added and the
e1000 SDM does not have any more information.
Jack, can you take a look at the patch and commit if it looks alright?
best
Neel
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