netdev - Re: [PATCH] net: dsa: mv88e6xxx: Skip cmode writable for mv88e6*41 if unchanged

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Date:   Sat, 23 Apr 2022 23:59:50 +1000
From:   Nathan Rossi <nathan@...hanrossi.com>
To:     Marek Behún <kabel@...nel.org>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH] net: dsa: mv88e6xxx: Skip cmode writable for mv88e6*41 if unchanged

On Sat, 23 Apr 2022 at 23:25, Marek Behún <kabel@...nel.org> wrote:
>
> On Sat, 23 Apr 2022 13:20:35 +0000
> Nathan Rossi <nathan@...hanrossi.com> wrote:
>
> > The mv88e6341_port_set_cmode function always calls the set writable
> > regardless of whether the current cmode is different from the desired
> > cmode. This is problematic for specific configurations of the mv88e6341
> > and mv88e6141 (in single chip adddressing mode?) where the hidden
> > registers are not accessible.
>
> I don't have a problem with skipping setting cmode writable if cmode is
> not being changed. But hidden registers should be accessible regardless
> of whether you are using single chip addressing mode or not. You need
> to find why it isn't working for you, this is a bug.

I did try to debug the hidden register access, unfortunately with the
device I have the hidden registers do not behave correctly. It simply
times out waiting for the busy bit to change. I was not sure the
reason why and suspected it was something specific to the single mode,
and unfortunately the only information I have regarding these
registers is the kernel code itself. Perhaps it is specific to some
other pin configuration or the specific chip revision? If you have any
additional information for these hidden registers it would be very
helpful in debugging. For reference the device is a MV88E6141,
manufactured in 2019 week 47 (in a Netgate SG-3100).

Thanks,
Nathan

>
> Marek