linux-kernel - Re: [PATCH net-next 6/9] net: phy: add backplane kr driver support

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Date:   Wed, 1 Apr 2020 13:35:36 +0000
From:   Florinel Iordache <florinel.iordache@....com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "hkallweit1@...il.com" <hkallweit1@...il.com>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "corbet@....net" <corbet@....net>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        Leo Li <leoyang.li@....com>,
        "Madalin Bucur (OSS)" <madalin.bucur@....nxp.com>,
        Ioana Ciornei <ioana.ciornei@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Florinel Iordache <florinel.iordache@....com>
Subject: Re: [PATCH net-next 6/9] net: phy: add backplane kr driver support

> On Thu, Mar 26, 2020 at 03:51:19PM +0200, Florinel Iordache wrote:
> > +static void setup_supported_linkmode(struct phy_device *bpphy) {
> > +     struct backplane_phy_info *bp_phy = bpphy->priv;
> 
> I'm not sure it is a good idea to completely take over phydev->priv like this, in
> what is just helper code. What if the PHY driver needs memory of its own? There
> are a few examples of this already in other PHY drivers. Could a KR PHY contain
> a temperature sensor? Could it contain statistics counters which need
> accumulating?
> 
>         Andrew

Backplane KR driver allocates memory for structure backplane_phy_info
which is saved in phydev->priv. After all this is the purpose of priv
according to its description in phy.h: <<private data pointer For use
by PHYs to maintain extra state>>. Here the priv is used to maintain
extra state needed for backplane. This way the backplane specific data
becomes available for all PHY callbacks (defined in struct phy_driver)
that receive a pointer to phy_device structure. This initial version
doesn't include accumulating statistics counters but we have in plan
to add these in future versions. The counters will be kept in specific
structures as members of the main backplane data mentioned above
and entire support will be integrated with ethtool.

Florin.