netdev - Re: [PATCH RFC net-next 05/12] net: dsa: bcm_sf2: convert to phylink_generic

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Date:   Sun, 5 Dec 2021 12:58:40 +0000
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        George McCollister <george.mccollister@...il.com>,
        Hauke Mehrtens <hauke@...ke-m.de>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        Vladimir Oltean <vladimir.oltean@....com>,
        Woojung Huh <woojung.huh@...rochip.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        UNGLinuxDriver@...rochip.com
Subject: Re: [PATCH RFC net-next 05/12] net: dsa: bcm_sf2: convert to
 phylink_generic_validate()

On Sat, Dec 04, 2021 at 04:01:32PM +0100, Andrew Lunn wrote:
> > The order of 1000baseKX/Full and 1000baseT/Full is such that we
> > prefer 1000baseKX/Full over 1000baseT/Full, but 1000baseKX/Full is
> > a lot rarer than 1000baseT/Full, and thus is much less likely to
> > be preferred.
> > 
> > This causes phylink problems - it means a fixed link specifying a
> > speed of 1G and full duplex gets an ethtool linkmode of 1000baseKX/Full
> > rather than 1000baseT/Full as would be expected - and since we offer
> > userspace a software emulation of a conventional copper PHY, we want
> > to offer copper modes in preference to anything else. However, we do
> > still want to allow the rarer modes as well.
> 
> 2.5G already places T before X, so it makes it more uniform with that.
> 
> For 10G, T comes last. Maybe we should also consider this case?  Do we
> see more 10G copper than fibre/backplane?

For a fixed link, I'm not sure - but given that speeds higher than 1G
can't be emulated by the C22 PHY emulation, does it really matter?

Looking through the DTs that we have in the kernel tree, we have some
fixed-links at 10G speed, and no one has complained, so I'd suggest
leaving sleeping dogs and all that.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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