netdev - Re: [PATCH net-next v1 7/7] ethtool: add interface to interact with Ethernet Power Equipment

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Date:   Sun, 21 Aug 2022 06:39:32 +0200
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Heiner Kallweit <hkallweit1@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Russell King <linux@...linux.org.uk>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Jonathan Corbet <corbet@....net>, kernel@...gutronix.de,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        devicetree@...r.kernel.org, linux-doc@...r.kernel.org,
        David Jander <david@...tonic.nl>
Subject: Re: [PATCH net-next v1 7/7] ethtool: add interface to interact with
 Ethernet Power Equipment

On Sat, Aug 20, 2022 at 08:16:18PM +0200, Andrew Lunn wrote:
> On Fri, Aug 19, 2022 at 02:01:09PM +0200, Oleksij Rempel wrote:
> > Add interface to support Power Sourcing Equipment. At current step it
> > provides generic way to address all variants of PSE devices as defined
> > in IEEE 802.3-2018 but support only objects specified for IEEE 802.3-2018 104.4
> > PoDL Power Sourcing Equipment (PSE).
> > 
> > Currently supported and mandatory objects are:
> > IEEE 802.3-2018 30.15.1.1.3 aPoDLPSEPowerDetectionStatus
> > IEEE 802.3-2018 30.15.1.1.2 aPoDLPSEAdminState
> > IEEE 802.3-2018 30.15.1.2.1 acPoDLPSEAdminControl
> > 
> > This is minimal interface needed to control PSE on each separate
> > ethernet port but it provides not all mandatory objects specified in
> > IEEE 802.3-2018.
> 
> > +static int pse_get_pse_attributs(struct net_device *dev,
> > +				 struct pse_reply_data *data)
> > +{
> > +	struct phy_device *phydev = dev->phydev;
> > +	int ret;
> > +
> > +	if (!phydev)
> > +		return -EOPNOTSUPP;
> > +
> > +	mutex_lock(&phydev->lock);
> > +	if (!phydev->psec) {
> > +		ret = -EOPNOTSUPP;
> > +		goto error_unlock;
> > +	}
> > +
> > +	ret = pse_podl_get_admin_sate(phydev->psec);
> > +	if (ret < 0)
> > +		goto error_unlock;
> > +
> > +	data->podl_pse_admin_state = ret;
> > +
> > +	ret = pse_podl_get_pw_d_status(phydev->psec);
> > +	if (ret < 0)
> > +		goto error_unlock;
> > +
> > +	data->podl_pse_pw_d_status = ret;
> 
> I'm wondering how this is going to scale. At some point, i expect
> there will be an implementation that follows C45.2.9. I see 14 values
> which could be returned. I don't think 14 ops in the driver structure
> makes sense. Plus c30.15.1 defines other values.
> 
> The nice thing about netlink is you can have as many or are little
> attributes in the message as you want. For cable testing, i made use
> of this. There is no standardisation, different PHYs offer different
> sorts of results. So i made the API flexible. The PHY puts whatever
> results it has into the message, and ethtool(1) just walks the message
> and prints what is in it.
> 
> I'm wondering if we want a similar sort of API here?
> net/ethtool/pse-pd.c allocates the netlink messages, adds the header,
> and then passes it to the driver. The driver then uses helpers from
> ethtool to add whatever attributes it wants to the message. pse-pd
> then completes the message, and returns it to user space? This seems
> like it will scale better.

Yes. Sounds good. I'll make a new version.

Regards,
Oleksij
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