[Intel-wired-lan] [PATCH net] ixgbe: set X550 MDIO speed before talking to PHY

[Cyril Novikov]

The MDIO bus speed must be initialized before talking to the PHY the first
time in order to avoid talking to it using a speed that the PHY doesn't
support.

This fixes HW initialization error -17 (IXGBE_ERR_PHY_ADDR_INVALID) on
Denverton CPUs (a.k.a. the Atom C3000 family) on ports with a 10Gb network
plugged in. On those devices, HLREG0[MDCSPD] resets to 1, which combined
with the 10Gb network results in a 24MHz MDIO speed, which is apparently
too fast for the connected PHY. PHY register reads over MDIO bus return
garbage, leading to initialization failure.

Signed-off-by: Cyril Novikov <cnovikov at lynx.com>
---
 drivers/net/ethernet/intel/ixgbe/ixgbe_x550.c | 3 +++
 1 file changed, 3 insertions(+)

Reproduced with Linux kernel 4.19 and 5.15-rc7. Can be reproduced using
the following setup:

* Use an Atom C3000 family system with at least one X550 LAN on the SoC
* Disable PXE or other BIOS network initialization if possible
  (the interface must not be initialized before Linux boots)
* Connect a live 10Gb Ethernet cable to an X550 port
* Power cycle (not reset, doesn't always work) the system and boot Linux
* Observe: ixgbe interfaces w/ 10GbE cables plugged in fail with error -17

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_x550.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_x550.c
index 9724ffb16518..e4b50c7781ff 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_x550.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_x550.c
@@ -3405,6 +3405,9 @@ static s32 ixgbe_reset_hw_X550em(struct ixgbe_hw *hw)
 	/* flush pending Tx transactions */
 	ixgbe_clear_tx_pending(hw);
 
+	/* set MDIO speed before talking to the PHY in case it's the 1st time */
+	ixgbe_set_mdio_speed(hw);
+
 	/* PHY ops must be identified and initialized prior to reset */
 	status = hw->phy.ops.init(hw);
 	if (status == IXGBE_ERR_SFP_NOT_SUPPORTED ||
-- 
2.19.1-412.replication