netdev - RE: [Intel-wired-lan] [PATCH v2 net] ixgbe: set X550 MDIO speed before talking to PHY

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Date:   Fri, 24 Dec 2021 00:23:49 +0000
From:   "Brelinski, Tony" <tony.brelinski@...el.com>
To:     Cyril Novikov <cnovikov@...x.com>,
        "David S. Miller" <davem@...emloft.net>
CC:     Jakub Kicinski <kuba@...nel.org>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [Intel-wired-lan] [PATCH v2 net] ixgbe: set X550 MDIO speed
 before talking to PHY

> -----Original Message-----
> From: Intel-wired-lan <intel-wired-lan-bounces@...osl.org> On Behalf Of
> Cyril Novikov
> Sent: Monday, November 1, 2021 6:40 PM
> To: David S. Miller <davem@...emloft.net>
> Cc: Jakub Kicinski <kuba@...nel.org>; intel-wired-lan@...ts.osuosl.org;
> netdev@...r.kernel.org
> Subject: [Intel-wired-lan] [PATCH v2 net] ixgbe: set X550 MDIO speed before
> talking to PHY
> 
> 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.
> 
> 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 X552 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
> 
> Signed-off-by: Cyril Novikov <cnovikov@...x.com>
> Fixes: e84db7272798 ("ixgbe: Introduce function to control MDIO speed")
> ---
>  drivers/net/ethernet/intel/ixgbe/ixgbe_x550.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> Patch v2 addresses review comments: add a Fixed line, move reproduction
> steps to the commit message. No changes to the code.

Tested-by: Tony Brelinski <tony.brelinski@...el.com>