netdev - Re: [PATCH v4 net-next 2/8] net: phylink: introduce generic method to query PHY in-band autoneg capability

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Date:   Fri, 18 Nov 2022 17:42:41 +0200
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Sean Anderson <sean.anderson@...o.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>,
        Russell King <linux@...linux.org.uk>,
        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>,
        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 2/8] net: phylink: introduce generic method
 to query PHY in-band autoneg capability

On Fri, Nov 18, 2022 at 10:11:06AM -0500, Sean Anderson wrote:
> > +enum phy_an_inband {
> > +	PHY_AN_INBAND_UNKNOWN		= BIT(0),
> 
> Shouldn't this be something like
> 
> 	PHY_AN_INBAND_UNKNOWN		= 0,
> 
> ?

Could be 0 as well. The code explicitly tests against PHY_AN_INBAND_UNKNOWN
everywhere, so the precise value doesn't matter too much.

> What does it mean if a phy returns e.g. 0b101?

You mean PHY_AN_INBAND_ON | PHY_AN_INBAND_UNKNOWN. Well, it doesn't mean
anything, it's not a valid return code. I didn't make the code too defensive
in this regard, because I didn't see a reason for making some pieces of
code defend themselves against other pieces of code. It's a bit mask of
3 bits where not all combinations are valid. Even if PHY_AN_INBAND_UNKNOWN
was defined as 0 instead of BIT(0), it would still be just as logically
invalid to return PHY_AN_INBAND_ON | PHY_AN_INBAND_UNKNOWN, but this
would be indistinguishable in machine code from just PHY_AN_INBAND_ON.

I don't know, I don't see a practical reason to make a change here.