[PATCH 0/4] [SRU] [X/raspi2] RaspberryPi 3B+: fix ethernet leds

Fri Nov 9 15:44:18 UTC 2018

BugLink: http://bugs.launchpad.net/bugs/1802320

Impact:

Using a xenial/raspi2 kernel on a RaspberryPi3B+ board, ethernet leds don't
blink (though ethernet port works fine).

Leds not working are due to a missing (actualy reverted) upstream stable patch
in xenial/raspi2 (1111a9 "UBUNTU: SAUCE: Revert "lan78xx: Correctly indicate
invalid OTP""), but reverting that patch uncovers another more severe bug: the
ethernet port stops working since two hardware registers are not updated when,
during bootup, the mac address is set (i explained this part of the bug in
detail here: https://lkml.org/lkml/2018/11/7/860).

When doing the initial enablement of the rpi3bp+ board in
xenial, i found that the ethernet port was not working and after a bisection i
found an upstream stable commit (the above "lan78xx: Correctly indicate invalid
OTP") that was causing it.

But it turned out that this patch was legit, and the buggy behaviour of the
lan78xx_read_otp() function (that was being fixed by the above "lan78xx:
Correctly indicate invalid OTP" patch) was actually hiding another bug in the
lan78xx ethernet driver:

https://lkml.org/lkml/2018/11/7/860

"
Upon invocation, lan78xx_init_mac_address() checks that the mac address present
in the RX_ADDRL & RX_ADDRH registers is a valid address, if not, it first tries
to read a new address from an external eeprom or the otp area, and in case both
read fail (or the address read back is invalid), it randomly generates a new
one.

Unfortunately, due to the way the above logic is laid out, if both
read_eeprom() and read_otp() fail, a new mac address is correctly generated but
is never written back to RX_ADDRL & RX_ADDRH, leaving the chip in an
incosistent state and with an invalid mac address (e.g. the nic appears to be
completely dead, and doesn't receive any packet, etc):

lan78xx_init_mac_address()
...
if (lan78xx_read_eeprom(addr ...) || lan78xx_read_otp(addr ...)) {
 if (is_valid_ether_addr(addr) {
  // nop...
 } else {
  random_ether_addr(addr);
 }

 // correctly writes back the new address
 lan78xx_write_reg(RX_ADDRL, addr ...);
 lan78xx_write_reg(RX_ADDRH, addr ...);
} else {
 // XXX if both eeprom and otp read fail, we land here and skip
 // XXX the RX_ADDRL & RX_ADDRH update above
 random_ether_addr(addr);
}

This bug went unnoticed because lan78xx_read_otp() was buggy itself and would
never fail, up until 4bfc338 "lan78xx: Correctly indicate invalid OTP" fixed it
and as a side effect uncovered this bug.
"

Upstream later decided to take an entire patch from 4.18.y instead of the fix i
proposed, but that is fine, and is one of the patch i'm presenting here (patch
003 "lan78xx: Read MAC address from DT if present").

Fix:

The whole fix consist in importing a new upstream patch from 4.18.y for the mac
address changing logic (patch 003), reverting two Raspberry BSP patches that
clash (and are obsoleted) by this new patch (patch 001 and 002), and then
reverting a SAUCE patch, or in other words, reapply the lan78xx_read_otp()
upstream fix (patch 004), that is the actual fix for the ethernet leds.

Chronologically, first the two reverts:

commit 3f25fbb82f00a80e9eb3be0ce60abebfc263c84a
Author: Paolo Pisati <paolo.pisati at canonical.com>
Date: Thu Nov 8 10:35:09 2018 +0000

    Revert "lan78xx: Ignore DT MAC address if already valid"

    This reverts commit 17f23a96597810ddd56b0c10584fce77d7c3707f.

    Signed-off-by: Paolo Pisati <paolo.pisati at canonical.com>

and

commit 6c8bdff882656296adc20b6ae0fb727483a73c7c
Author: Paolo Pisati <paolo.pisati at canonical.com>
Date: Thu Nov 8 10:35:11 2018 +0000

    Revert "lan78xx: Read MAC address from DT if present"

    This reverts commit a23d928781936b51a61a67a0799b77b2a6becfa2.

    Signed-off-by: Paolo Pisati <paolo.pisati at canonical.com>

then the upstream cherry pick for the mac changing logic:

commit 5d9c81e3aa1dd39dafd9a6ea30da05b26b655eca
Author: Phil Elwell <phil at raspberrypi.org>
Date: Thu Apr 19 17:59:38 2018 +0100

    lan78xx: Read MAC address from DT if present

    There is a standard mechanism for locating and using a MAC address from
    the Device Tree. Use this facility in the lan78xx driver to support
    applications without programmed EEPROM or OTP. At the same time,
    regularise the handling of the different address sources.

    Signed-off-by: Phil Elwell <phil at raspberrypi.org>
    Signed-off-by: David S. Miller <davem at davemloft.net>
    (cherry picked from commit 760db29bdc97b73ff60b091315ad787b1deb5cf5)
    Signed-off-by: Paolo Pisati <paolo.pisati at canonical.com>

and finally revert the SAUCE patch that fixes lan78xx_read_otp(), and makes the
led code work again:

commit 24dc8f22b15cc983e13a0ae88b372dd1bfad09f9
Author: Paolo Pisati <paolo.pisati at canonical.com>
Date: Thu Nov 8 10:37:17 2018 +0000

    Revert "UBUNTU: SAUCE: Revert "lan78xx: Correctly indicate invalid OTP""

    This reverts commit 1111a9e0bd2ebab88e736d8a9773df2ec76dc52c.

    Signed-off-by: Paolo Pisati <paolo.pisati at canonical.com>