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

From: Tim Harvey <tharvey@gateworks.com>
To: Andrew Lunn <andrew@lunn.ch>
Cc: Sean Anderson <sean.anderson@seco.com>,
	Vladimir Oltean <olteanv@gmail.com>,
	Heiner Kallweit <hkallweit1@gmail.com>,
	Russell King <linux@armlinux.org.uk>,
	netdev@vger.kernel.org, Eric Dumazet <edumazet@google.com>,
	"David S . Miller" <davem@davemloft.net>,
	linux-kernel@vger.kernel.org, Paolo Abeni <pabeni@redhat.com>,
	Jakub Kicinski <kuba@kernel.org>
Subject: Re: [PATCH] phy: aquantia: Configure SERDES mode by default
Date: Mon, 28 Nov 2022 16:20:42 -0800	[thread overview]
Message-ID: <CAJ+vNU1iDuFRbm-9+hzEgqZ=enL2yTkDJq6=7EtsQu3KFAxjDQ@mail.gmail.com> (raw)
In-Reply-To: <Y3bLlUk1wxzAqKmj@lunn.ch>

On Thu, Nov 17, 2022 at 4:03 PM Andrew Lunn <andrew@lunn.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