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SubjectRe: [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 <>
>> Sent: 2021年4月23日 12:37
>> To: Joakim Zhang <>
>> Cc: Shawn Guo <>; Sascha Hauer
>> <>; Andrew Lunn <>; Florian Fainelli
>> <>; Heiner Kallweit <>; Fugang
>> Duan <>;;
>>; dl-linux-imx <>; Fabio
>> Estevam <>; David Jander <>; Russell
>> King <>; Philippe Schenker
>> <>
>> 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

From an Ethernet MAC and PHY driver perspective, what I would imagine we
could have for a driver API is:

enum ethtool_loopback_mode {

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) {
ret = phy_loopback(ndev->phydev, mode);
/* 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

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