Re: net: phy: Dealing with 88e1543 dual-port mode - Russell King

From: Russell King - ARM Linux admin <linux@armlinux.org.uk>
To: Maxime Chevallier <maxime.chevallier@bootlin.com>
Cc: Andrew Lunn <andrew@lunn.ch>,
	Florian Fainelli <f.fainelli@gmail.com>,
	netdev@vger.kernel.org, Antoine Tenart <atenart@kernel.org>,
	Vivien Didelot <vivien.didelot@gmail.com>,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	Tobias Waldekranz <tobias@waldekranz.com>,
	"David S. Miller" <davem@davemloft.net>,
	linux-arm-kernel@lists.infradead.org,
	Heiner Kallweit <hkallweit1@gmail.com>
Subject: Re: net: phy: Dealing with 88e1543 dual-port mode
Date: Fri, 20 Nov 2020 10:25:38 +0000	[thread overview]
Message-ID: <20201120102538.GP1551@shell.armlinux.org.uk> (raw)
In-Reply-To: <20201120103601.313a166b@bootlin.com>

On Fri, Nov 20, 2020 at 10:36:01AM +0100, Maxime Chevallier wrote:
> So maybe we could be a bit more generic, with something along these lines :
> 
>     ethernet-phy@0 {
>         ...
> 
>         mdi {
>             port@0 {
>                 media = "10baseT", "100baseT", "1000baseT";
>                 pairs = <1>;
> 	    };
> 
>             port@1 {
>                 media = "1000baseX", "10gbaseR"
>             };
>         };
>     };

Don't forget that TP requires a minimum of two pairs. However, as
Andrew pointed out, we already have max-speed which can be used to
limit the speed below that which requires four pairs.

I have untested patches that allow the 88x3310 to be reconfigured
between 10GBASE-R and 1000BASE-X depending on the SFP connected -
untested because the I2C pull-ups on the Macchiatobin boards I have
are way too strong and it results in SFP EEPROM corruption and/or
failure to read the EEPROM.

> I also like the idea of having a way to express the "preferred" media,
> although I wonder if that's something we want to include in DT or that
> we would want to tweak at runtime, through ethtool for example.

I think preferred media should be configurable through ethtool -
which is preferred will be specific to the user's application.
However, there may be scope for DT to be able to specify the default
preferred media.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!

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