linux-kernel - Re: [PATCH net-next v3 0/6] provide generic net selftest support

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Date:   Wed, 28 Apr 2021 10:51:15 +0200
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     Joakim Zhang <qiangqing.zhang@....com>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Fabio Estevam <festevam@...il.com>,
        Fugang Duan <fugang.duan@....com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Russell King <linux@...linux.org.uk>,
        Philippe Schenker <philippe.schenker@...adex.com>,
        dl-linux-imx <linux-imx@....com>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        David Jander <david@...tonic.nl>,
        Shawn Guo <shawnguo@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Heiner Kallweit <hkallweit1@...il.com>
Subject: Re: [PATCH net-next v3 0/6] provide generic net selftest support

On Wed, Apr 28, 2021 at 08:06:05AM +0000, Joakim Zhang wrote:
> 
> Hi Florian,
> 
> > -----Original Message-----
> > From: Florian Fainelli <f.fainelli@...il.com>
> > Sent: 2021年4月28日 0:41
> > To: Joakim Zhang <qiangqing.zhang@....com>; Oleksij Rempel
> > <o.rempel@...gutronix.de>
> > Cc: Shawn Guo <shawnguo@...nel.org>; Sascha Hauer
> > <s.hauer@...gutronix.de>; Andrew Lunn <andrew@...n.ch>; Heiner Kallweit
> > <hkallweit1@...il.com>; Fugang Duan <fugang.duan@....com>;
> > kernel@...gutronix.de; netdev@...r.kernel.org;
> > linux-arm-kernel@...ts.infradead.org; linux-kernel@...r.kernel.org;
> > dl-linux-imx <linux-imx@....com>; Fabio Estevam <festevam@...il.com>;
> > David Jander <david@...tonic.nl>; Russell King <linux@...linux.org.uk>;
> > Philippe Schenker <philippe.schenker@...adex.com>
> > Subject: Re: [PATCH net-next v3 0/6] provide generic net selftest support
> > 
> > 
> > 
> > On 4/26/2021 9:48 PM, Joakim Zhang wrote:
> > >
> > >> -----Original Message-----
> > >> From: Oleksij Rempel <o.rempel@...gutronix.de>
> > >> Sent: 2021年4月23日 12:37
> > >> To: Joakim Zhang <qiangqing.zhang@....com>
> > >> Cc: Shawn Guo <shawnguo@...nel.org>; Sascha Hauer
> > >> <s.hauer@...gutronix.de>; Andrew Lunn <andrew@...n.ch>; Florian
> > >> Fainelli <f.fainelli@...il.com>; Heiner Kallweit
> > >> <hkallweit1@...il.com>; Fugang Duan <fugang.duan@....com>;
> > >> kernel@...gutronix.de; netdev@...r.kernel.org;
> > >> linux-arm-kernel@...ts.infradead.org;
> > >> linux-kernel@...r.kernel.org; dl-linux-imx <linux-imx@....com>; Fabio
> > >> Estevam <festevam@...il.com>; David Jander <david@...tonic.nl>;
> > >> Russell King <linux@...linux.org.uk>; Philippe Schenker
> > >> <philippe.schenker@...adex.com>
> > >> Subject: Re: [PATCH net-next v3 0/6] provide generic net selftest
> > >> support
> > >>
> > >> Hi Joakim,
> > >>
> > >> On Fri, Apr 23, 2021 at 03:18:32AM +0000, Joakim Zhang wrote:
> > >>>
> > >>> Hi Oleksij,
> > >>>
> > >>> I look both stmmac selftest code and this patch set. For stmmac, if
> > >>> PHY
> > >> doesn't support loopback, it will fallthrough to MAC loopback.
> > >>> You provide this generic net selftest support based on PHY loopback,
> > >>> I have a
> > >> question, is it possible to extend it also support MAC loopback later?
> > >>
> > >> Yes. If you have interest and time to implement it, please do.
> > >> It should be some kind of generic callback as phy_loopback() and if
> > >> PHY and MAC loopbacks are supported we need to tests both variants.
> > > Hi Oleksij,
> > >
> > > Yes, I can try to implement it when I am free, but I still have some questions:
> > > 1. Where we place the generic function? Such as mac_loopback().
> > > 2. MAC is different from PHY, need program different registers to enable
> > loopback on different SoCs, that means we need get MAC private data from
> > "struct net_device".
> > > So we need a callback for MAC drivers, where we extend this callback? Could
> > be "struct net_device_ops"? Such as ndo_set_loopback?
> > 
> > Even for PHY devices, if we implemented external PHY loopback in the future,
> > the programming would be different from one vendor to another. I am starting
> > to wonder if the existing ethtool self-tests are the best API to expose the ability
> > for an user to perform PHY and MAC loopback testing.
> > 
> > From an Ethernet MAC and PHY driver perspective, what I would imagine we
> > could have for a driver API is:
> > 
> > enum ethtool_loopback_mode {
> > 	ETHTOOL_LOOPBACK_OFF,
> > 	ETHTOOL_LOOPBACK_PHY_INTERNAL,
> > 	ETHTOOL_LOOPBACK_PHY_EXTERNAL,
> > 	ETHTOOL_LOOPBACK_MAC_INTERNAL,
> > 	ETHTOOL_LOOPBACK_MAC_EXTERNAL,
> > 	ETHTOOL_LOOPBACK_FIXTURE,
> > 	__ETHTOOL_LOOPBACK_MAX
> > };
> 
> What's the difference between internal and external loopback for both PHY and MAC? I am not familiar with these concepts. Thanks.

For example KSZ9031 PHY. It supports two loopback modes. See page 23:
https://ww1.microchip.com/downloads/en/DeviceDoc/00002096E.pdf

TI DP83TC811R-Q1 PHY supports 4 modes. See page 27:
https://www.ti.com/lit/ds/symlink/dp83tc811r-q1.pdf


> Best Regards,
> Joakim Zhang
> > 	int (*ndo_set_loopback_mode)(struct net_device *dev, enum
> > ethtool_loopback_mode mode);
> > 
> > and within the Ethernet MAC driver you would do something like this:
> > 
> > 	switch (mode) {
> > 	case ETHTOOL_LOOPBACK_PHY_INTERNAL:
> > 	case ETHTOOL_LOOPBACK_PHY_EXTERNAL:
> > 	case ETHTOOL_LOOPBACK_OFF:
> > 		ret = phy_loopback(ndev->phydev, mode);
> > 		break;
> > 	/* Other case statements implemented in driver */
> > 
> > we would need to change the signature of phy_loopback() to accept being
> > passed ethtool_loopback_mode so we can support different modes.
> > 
> > Whether we want to continue using the self-tests API, or if we implement a
> > new ethtool command in order to request a loopback operation is up for
> > discussion.
> > --
> > Florian

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