netdev - Re: [PATCH net-next 0/4] net: ethtool: Untangle PHYLIB dependency

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Message-ID: <20200702163424.GG752507@lunn.ch>
Date:   Thu, 2 Jul 2020 18:34:24 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Michal Kubecek <mkubecek@...e.cz>
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>,
        Jakub Kicinski <kuba@...nel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 0/4] net: ethtool: Untangle PHYLIB dependency

On Thu, Jul 02, 2020 at 05:56:52PM +0200, Michal Kubecek wrote:
> On Wed, Jul 01, 2020 at 09:29:38PM -0700, Florian Fainelli wrote:
> > Hi all,
> > 
> > This patch series untangles the ethtool netlink dependency with PHYLIB
> > which exists because the cable test feature calls directly into PHY
> > library functions. The approach taken here is to utilize a new set of
> > net_device_ops function pointers which are automatically set to the PHY
> > library variants when a network device driver attaches to a PHY device.
> 
> I'm not sure about the idea of creating a copy of netdev_ops for each
> device using phylib. First, there would be some overhead (just checked
> my 5.8-rc3 kernel, struct netdev_ops is 632 bytes). Second, there is
> quite frequent pattern of comparing dev->netdev_ops against known
> constants to check if a network device is of certain type; I can't say
> for sure if it is also used with devices using phylib in existing code
> but it feels risky.

I agree with Michal here. I don't like this.

I think we need phylib to register a set of ops with ethtool when it
loads. It would also allow us to clean up phy_ethtool_get_strings(),
phy_ethtool_get_sset_count(), phy_ethtool_get_stats().

      Andrew