netdev - Re: [PATCH net-next v3 1/2] ethtool: provide UAPI for PHY Signal Quality Index (SQI)

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Date:   Wed, 20 May 2020 17:23:50 +0200
From:   Michal Kubecek <mkubecek@...e.cz>
To:     netdev@...r.kernel.org
Cc:     Oleksij Rempel <o.rempel@...gutronix.de>,
        Marek Vasut <marex@...x.de>, Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Jonathan Corbet <corbet@....net>, 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 Signal
 Quality Index (SQI)

On Wed, May 20, 2020 at 05:07:11PM +0200, Oleksij Rempel wrote:
> On Wed, May 20, 2020 at 04:45:44PM +0200, Michal Kubecek wrote:
> > On Wed, May 20, 2020 at 08:29:14AM +0200, Oleksij Rempel wrote:
> > > Signal Quality Index is a mandatory value required by "OPEN Alliance
> > > SIG" for the 100Base-T1 PHYs [1]. This indicator can be used for cable
> > > integrity diagnostic and investigating other noise sources and
> > > implement by at least two vendors: NXP[2] and TI[3].
> > > 
> > > [1] http://www.opensig.org/download/document/218/Advanced_PHY_features_for_automotive_Ethernet_V1.0.pdf
> > > [2] https://www.nxp.com/docs/en/data-sheet/TJA1100.pdf
> > > [3] https://www.ti.com/product/DP83TC811R-Q1
> > > 
> > > Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
> > > ---
> > 
> > This looks good to me, there is just one thing I'm not sure about:
> > 
> > > diff --git a/include/linux/phy.h b/include/linux/phy.h
> > > index 59344db43fcb1..950ba479754bd 100644
> > > --- a/include/linux/phy.h
> > > +++ b/include/linux/phy.h
> > > @@ -706,6 +706,8 @@ struct phy_driver {
> > >  			    struct ethtool_tunable *tuna,
> > >  			    const void *data);
> > >  	int (*set_loopback)(struct phy_device *dev, bool enable);
> > > +	int (*get_sqi)(struct phy_device *dev);
> > > +	int (*get_sqi_max)(struct phy_device *dev);
> > >  };
> > >  #define to_phy_driver(d) container_of(to_mdio_common_driver(d),		\
> > >  				      struct phy_driver, mdiodrv)
> > 
> > I'm not sure if it's a good idea to define two separate callbacks. It
> > means adding two pointers instead of one (for every instance of the
> > structure, not only those implementing them), doing two calls, running
> > the same checks twice, locking twice, checking the result twice.
> > 
> > Also, passing a structure pointer would mean less code changed if we
> > decide to add more related state values later.
> > 
> > What do you think?
> > 
> > If you don't agree, I have no objections so
> > 
> > Reviewed-by: Michal Kubecek <mkubecek@...e.cz>
> 
> I have no strong opinion on it. Should I rework it?

It's up to you. It was a suggestion for possible improvement but I have
no problem with this version being applied.

Michal