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    SubjectRe: [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@gmail.com>
    > > Sent: 2021年4月28日 0:41
    > > To: Joakim Zhang <qiangqing.zhang@nxp.com>; Oleksij Rempel
    > > <o.rempel@pengutronix.de>
    > > Cc: Shawn Guo <shawnguo@kernel.org>; Sascha Hauer
    > > <s.hauer@pengutronix.de>; Andrew Lunn <andrew@lunn.ch>; Heiner Kallweit
    > > <hkallweit1@gmail.com>; Fugang Duan <fugang.duan@nxp.com>;
    > > kernel@pengutronix.de; netdev@vger.kernel.org;
    > > linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org;
    > > dl-linux-imx <linux-imx@nxp.com>; Fabio Estevam <festevam@gmail.com>;
    > > David Jander <david@protonic.nl>; Russell King <linux@armlinux.org.uk>;
    > > Philippe Schenker <philippe.schenker@toradex.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@pengutronix.de>
    > > >> Sent: 2021年4月23日 12:37
    > > >> To: Joakim Zhang <qiangqing.zhang@nxp.com>
    > > >> Cc: Shawn Guo <shawnguo@kernel.org>; Sascha Hauer
    > > >> <s.hauer@pengutronix.de>; Andrew Lunn <andrew@lunn.ch>; Florian
    > > >> Fainelli <f.fainelli@gmail.com>; Heiner Kallweit
    > > >> <hkallweit1@gmail.com>; Fugang Duan <fugang.duan@nxp.com>;
    > > >> kernel@pengutronix.de; netdev@vger.kernel.org;
    > > >> linux-arm-kernel@lists.infradead.org;
    > > >> linux-kernel@vger.kernel.org; dl-linux-imx <linux-imx@nxp.com>; Fabio
    > > >> Estevam <festevam@gmail.com>; David Jander <david@protonic.nl>;
    > > >> Russell King <linux@armlinux.org.uk>; Philippe Schenker
    > > >> <philippe.schenker@toradex.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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