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

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Message-ID: <89af2e39-fe5c-c285-7805-8c7a6a5a2e51@molgen.mpg.de>
Date:   Fri, 29 Oct 2021 08:47:45 +0200
From:   Paul Menzel <pmenzel@...gen.mpg.de>
To:     Cyril Novikov <cnovikov@...x.com>
Cc:     Jakub Kicinski <kuba@...nel.org>, intel-wired-lan@...ts.osuosl.org,
        netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>
Subject: Re: [Intel-wired-lan] [PATCH net] ixgbe: set X550 MDIO speed before
 talking to PHY

Dear Cyril,


On 29.10.21 03:03, Cyril Novikov wrote:
> 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.

Maybe add a Fixes tag?

> Signed-off-by: Cyril Novikov <cnovikov@...x.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

Why not add that to the commit message?

> 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 ||
> 

Is `ixgbe_set_mdio_speed(hw)` at the end of the function then still needed?


Kind regards,

Paul