RE: [PATCH net-next v3 0/6] provide generic net selftest support

[Joakim Zhang]

Hi Florian,

> -----Original Message-----
> From: Florian Fainelli <f.fainelli@xxxxxxxxx>
> Sent: 2021年4月28日 0:41
> To: Joakim Zhang <qiangqing.zhang@xxxxxxx>; Oleksij Rempel
> <o.rempel@xxxxxxxxxxxxxx>
> Cc: Shawn Guo <shawnguo@xxxxxxxxxx>; Sascha Hauer
> <s.hauer@xxxxxxxxxxxxxx>; Andrew Lunn <andrew@xxxxxxx>; Heiner Kallweit
> <hkallweit1@xxxxxxxxx>; Fugang Duan <fugang.duan@xxxxxxx>;
> kernel@xxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx;
> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> dl-linux-imx <linux-imx@xxxxxxx>; Fabio Estevam <festevam@xxxxxxxxx>;
> David Jander <david@xxxxxxxxxxx>; Russell King <linux@xxxxxxxxxxxxxxx>;
> Philippe Schenker <philippe.schenker@xxxxxxxxxxx>
> 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@xxxxxxxxxxxxxx>
> >> Sent: 2021年4月23日 12:37
> >> To: Joakim Zhang <qiangqing.zhang@xxxxxxx>
> >> Cc: Shawn Guo <shawnguo@xxxxxxxxxx>; Sascha Hauer
> >> <s.hauer@xxxxxxxxxxxxxx>; Andrew Lunn <andrew@xxxxxxx>; Florian
> >> Fainelli <f.fainelli@xxxxxxxxx>; Heiner Kallweit
> >> <hkallweit1@xxxxxxxxx>; Fugang Duan <fugang.duan@xxxxxxx>;
> >> kernel@xxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx;
> >> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx;
> >> linux-kernel@xxxxxxxxxxxxxxx; dl-linux-imx <linux-imx@xxxxxxx>; Fabio
> >> Estevam <festevam@xxxxxxxxx>; David Jander <david@xxxxxxxxxxx>;
> >> Russell King <linux@xxxxxxxxxxxxxxx>; Philippe Schenker
> >> <philippe.schenker@xxxxxxxxxxx>
> >> 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.

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