netdev - Re: [PATCH v4 net-next 3/8] net: phy: bcm84881: move the in-band capability check where it belongs

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Message-ID: <Y3yYo63kj+ACdkW1@shell.armlinux.org.uk>
Date:   Tue, 22 Nov 2022 09:38:43 +0000
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        UNGLinuxDriver@...rochip.com,
        bcm-kernel-feedback-list@...adcom.com,
        Madalin Bucur <madalin.bucur@....nxp.com>,
        Camelia Groza <camelia.groza@....com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Ioana Ciornei <ioana.ciornei@....com>,
        Maxim Kochetkov <fido_max@...ox.ru>,
        Sean Anderson <sean.anderson@...o.com>,
        Antoine Tenart <atenart@...nel.org>,
        Michael Walle <michael@...le.cc>,
        Raag Jadav <raagjadav@...il.com>,
        Siddharth Vadapalli <s-vadapalli@...com>,
        Ong Boon Leong <boon.leong.ong@...el.com>,
        Colin Foster <colin.foster@...advantage.com>,
        Marek Behun <marek.behun@....cz>
Subject: Re: [PATCH v4 net-next 3/8] net: phy: bcm84881: move the in-band
 capability check where it belongs

On Fri, Nov 18, 2022 at 02:01:19AM +0200, Vladimir Oltean wrote:
> Now that there is a generic interface through which phylink can query
> PHY drivers whether they support various forms of in-band autoneg, use
> that and delete the special case from phylink.c.
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>

I think I'd prefer to see patch 2 and patch 3 first in this series
(patch 3 without the phylink change). Possibly followed by other PHY
driver patches adding the validate_an_inband function, but that's not
important. Then the next patch can be patch 1 and the phylink part of
this patch combined - which makes the changes to phylink smaller as
there's no need to move the phylink_phy_no_inband() function and then
delete it a few patches later.

Also, if we get the Marvell driver implementing validate_an_inband()
then I believe we can get rid of other parts of this patch - 88E1111 is
the commonly used accessible PHY on gigabit SFPs, as this PHY implements
I2C access natively. As I mentioned, Marvell PHYs can be set to no
inband, requiring inband, or inband with bypass mode enabled. So we
need to decide how we deal with that - especially if we're going to be
changing the mode from 1000base-X to SGMII (which we do on some SFP
modules so they work at 10/100/1000.)

In that regard, I'm not entirely convinced that validate_an_inband()
covers the functionality we need - as reading the config register on
Marvell hardware doesn't guarantee that we're reading the right mode -
the PHY may be in 1000base-X, and we might change it to
SGMII-with-bypass - I'd need to go through the PHY datasheets to check
what we actually do.

Changing what the PHY driver does would be a recipe for regressions,
especially for drivers that do not use phylink.

Sorry, the above is a bit rambling, but are my thoughts on the current
approach.

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