netdev - Re: [PATCH] phy: aquantia: Configure SERDES mode by default

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Date:   Mon, 28 Nov 2022 16:20:42 -0800
From:   Tim Harvey <tharvey@...eworks.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Sean Anderson <sean.anderson@...o.com>,
        Vladimir Oltean <olteanv@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>, netdev@...r.kernel.org,
        Eric Dumazet <edumazet@...gle.com>,
        "David S . Miller" <davem@...emloft.net>,
        linux-kernel@...r.kernel.org, Paolo Abeni <pabeni@...hat.com>,
        Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH] phy: aquantia: Configure SERDES mode by default

On Thu, Nov 17, 2022 at 4:03 PM Andrew Lunn <andrew@...n.ch> wrote:
>
> > Well, part of my goal in sending out this patch is to get some feedback
> > on the right thing to do here. As I see it, there are three ways of
> > configuring this phy:
> >
> > - Always rate adapt to whatever the initial phy interface mode is
> > - Switch phy interfaces depending on the link speed
> > - Do whatever the firmware sets up
>
> My understanding of the aQuantia firmware is that it is split into two
> parts. The first is the actual firmware that runs on the PHY. The
> second is provisioning, which seems to be a bunch of instructions to
> put value X in register Y. It seems like aQuantia, now Marvell, give
> different provisioning to different customers.
>
> What this means is, you cannot really trust any register contains what
> you want, that your devices does the same as somebody elses' device in
> its reset state.
>
> So i would say, "Do whatever the firmware sets up" is the worst
> choice. Assume nothing, set every register which is important to the
> correct value.
>
>         Andrew

Andrew,

Sorry for the late reply!

That's exactly what the firmware is doing. According to a Marvell FAE
they add 'provisioning' of registers to the firmware to ease their
support effort. That didn't at all ease things for me because I was
pointed to the wrong firmware by another FAE which led to all of this.

In my case my device-tree is setting the interface to xfi (10g) yet
the firmware has provisioned the link for xfi/2 (5g) - a warning would
have probably helped us all understand the issue but again I was just
pointed to the wrong firmware without an explanation of how their
firmware works.

Tim