netdev - Re: [PATCH net-next 1/2] ixgbe: register a mdiobus

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Date:   Fri, 30 Nov 2018 17:34:37 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Steve Douthit <stephend@...icom-usa.com>
Cc:     Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 1/2] ixgbe: register a mdiobus

> Yep, registering multiple interfaces is wrong.  The first board I tested
> against only had a single MAC enabled (they can be disabled/hidden via
> straps) so it just happened to work.

Hi Steve

Can you hide any/all via straps, or is 00.0 always guaranteed to
exist?

> The Intel C3xxx family of SoCs have up to four ixgbe MACs.  These are
> structured as two devices of two functions each on fixed internal root
> ports.
> 
> from lspci:
> <snip>
>             +-16.0-[05]--+-00.0
>             |            \-00.1
>             +-17.0-[06]--+-00.0
>             |            \-00.1
> <snip>

Is there any other hardware resource which is shared between the MAC
interfaces? I'm just wondering if the driver has already solved this
once. Is there an EEPROM per interface for the MAC address, or one
shared EEPROM?

Ah, how about using the 'cards_found' found variable. It is not
perfect, in that it is not decremented in ixgb_remove(), and i wonder
about race conditions since there does not appear to be any lock when
it is incremented. But if cards_found == 0, register the MDIO bus.

   Andrew