netdev - Re: [PATCH net-next v2 3/3] net: ethtool: Remove PHYLIB direct dependency

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Message-ID: <20200706195603.GA893522@lunn.ch>
Date:   Mon, 6 Jul 2020 21:56:03 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Florian Fainelli <f.fainelli@...il.com>, netdev@...r.kernel.org,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>,
        Michal Kubecek <mkubecek@...e.cz>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next v2 3/3] net: ethtool: Remove PHYLIB direct
 dependency

On Mon, Jul 06, 2020 at 11:40:00AM -0700, Jakub Kicinski wrote:
> On Sun,  5 Jul 2020 21:27:58 -0700 Florian Fainelli wrote:
> > +	ops = ethtool_phy_ops;
> > +	if (!ops || !ops->start_cable_test) {
> 
> nit: don't think member-by-member checking is necessary. We don't
> expect there to be any alternative versions of the ops, right?

I would not like to see anything else registering an ops. So i think
taking an Opps would be a good indication somebody is doing something
wrong and needs fixing.

> We could even risk a direct call:
> 
> #if IS_REACHABLE(CONFIG_PHYLIB)
> static inline int do_x()
> {
> 	return __do_x();
> }
> #else
> static inline int do_x()
> {
> 	if (!ops)
> 		return -EOPNOTSUPP;
> 	return ops->do_x();
> }
> #endif
> 
> But that's perhaps doing too much...

I would say it is too far. Two ways of doing the same thing requires
twice as much testing. And these are not hot paths where we want to
eliminate as many instructions and trampolines as possible.

	  Andrew