linux-kernel - Re: [PATCH net-next v3 1/2] ethtool: provide UAPI for PHY master/slave configuration.

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Message-ID: <20200430122551.GB8934@lion.mk-sys.cz>
Date:   Thu, 30 Apr 2020 14:25:51 +0200
From:   Michal Kubecek <mkubecek@...e.cz>
To:     Oleksij Rempel <o.rempel@...gutronix.de>
Cc:     Marek Vasut <marex@...x.de>, Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Jonathan Corbet <corbet@....net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Russell King <linux@...linux.org.uk>,
        mkl@...gutronix.de, kernel@...gutronix.de,
        David Jander <david@...tonic.nl>,
        Jakub Kicinski <kuba@...nel.org>,
        Christian Herber <christian.herber@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Heiner Kallweit <hkallweit1@...il.com>
Subject: Re: [PATCH net-next v3 1/2] ethtool: provide UAPI for PHY
 master/slave configuration.

On Thu, Apr 30, 2020 at 02:09:45PM +0200, Oleksij Rempel wrote:
> > > > > @@ -119,7 +123,12 @@ static int linkmodes_fill_reply(struct sk_buff *skb,
> > > > >  	}
> > > > >  
> > > > >  	if (nla_put_u32(skb, ETHTOOL_A_LINKMODES_SPEED, lsettings->speed) ||
> > > > > -	    nla_put_u8(skb, ETHTOOL_A_LINKMODES_DUPLEX, lsettings->duplex))
> > > > > +	    nla_put_u8(skb, ETHTOOL_A_LINKMODES_DUPLEX, lsettings->duplex) ||
> > > > > +	    nla_put_u8(skb, ETHTOOL_A_LINKMODES_MASTER_SLAVE_CFG,
> > > > > +		       lsettings->master_slave_cfg) ||
> > > > > +	    nla_put_u8(skb, ETHTOOL_A_LINKMODES_MASTER_SLAVE_STATE,
> > > > > +		       lsettings->master_slave_state))
> > > > > +
> > > > >  		return -EMSGSIZE;
> > > > 
> > > > From the two handlers you introduced, it seems we only get CFG_UNKNOWN
> > > > or STATE_UNKNOWN if driver or device does not support the feature at all
> > > > so it would be IMHO more appropriate to omit the attribute in such case.
> > > 
> > > STATE_UNKNOWN is returned if link is not active.
> > 
> > How about distinguishing the two cases then? Omitting both if CFG is
> > CFG_UNKNOWN (i.e. driver does not support the feature) and sending
> > STATE=STATE_UNKNOWN to userspace only if we know it's a meaningful value
> > actually reported by the driver?
> 
> Hm... after thinking about it, we should keep state and config
> separately. The TJA1102 PHY do not provide actual state. Even no error
> related to Master/Master conflict. I reworked the code to have
> unsupported and unknown values.  In case we know, that state or config
> is not supported, it will not be exported to the user space.

Sounds good to me, splitting "unsupported" and "unknown" states will be
probably the best option.

Michal