netdev - Re: FWD: Re: [PATCH net-next v1 1/1] net: dsa: microchip: ksz8: Make flow control, speed, and duplex on CPU port configurable

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Date:   Tue, 11 Apr 2023 14:16:09 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     Oleksij Rempel <o.rempel@...gutronix.de>,
        Andrew Lunn <andrew@...n.ch>,
        Woojung Huh <woojung.huh@...rochip.com>,
        Arun Ramadoss <arun.ramadoss@...rochip.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        netdev@...r.kernel.org, UNGLinuxDriver@...rochip.com,
        Eric Dumazet <edumazet@...gle.com>, kernel@...gutronix.de,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: FWD: Re: [PATCH net-next v1 1/1] net: dsa: microchip: ksz8: Make
 flow control, speed, and duplex on CPU port configurable

On Tue, Apr 11, 2023 at 10:17:47AM +0100, Russell King (Oracle) wrote:
> Since we can't manually control the tx and rx pause enables, I think
> the only sensible way forward with this would be to either globally
> disable pause on the device, and not report support for any pause
> modes,

This implies restarting autoneg on all the other switch ports when one
port's flow control mode is changed?

> or report support for all pause modes, advertise '11' and
> let the hardware control it (which means the ethtool configuration
> for pause would not be functional.)
> 
> This needs to be commented in the driver so that in the future we
> remember why this has been done.
> 
> Maybe Andrew and/or Vladimir also have an opinion to share about the
> best approach here?

I don't object to documenting that manually forcing flow control off is
broken and leaving it at that (and the way to force it off would be to
not advertise any of the 2 bits).

But why advertise only 11 (Asym_Pause | Pause) when the PHYs integrated
here have the advertisement configurable (presumably also through the
micrel.c PHY driver)? They would advertise in accordance with ethtool, no?

I may have missed something.