Re: [PATCH] net: phy: genphy_loopback: fix loopback failed when speed is unknown

[huangguangbin (A)]

On 2022/4/1 20:14, Andrew Lunn wrote:
> > > O.K. So it should be set into 10M half duplex. But why does this cause
> > > it not to loopback packets? Does the PHY you are using not actually
> > > support 10 Half? Why does it need to be the same speed as when the
> > > link was up? And why does it actually set LSTATUS indicating there is
> > > link?
> > >
> > > Is this a generic problem, all PHYs are like this, or is this specific
> > > to the PHY you are using? Maybe this PHY needs its own loopback
> > > function because it does something odd?
> >
> > It looks for me like attempt to fix loopback test for setup without active
> > link partner. Correct?
>
> You should not need a link partner for loopback to work. This is local
> loopback. The PHY is also saying it has link, if the LSTATUS bit is
> set. So i don't see why previous speed is relevant hear. This seems to
> me to be an issue for this particular PHY.
>
> What i don't like about this patch is that it is not deterministic
> what mode the PHY will end up in if speed is unknown. Without the
> patch, it is 10Mbps, which is historically a sensible default.
>
> If this PHY has never had link, what speed does it use? Does it still
> work in that case?
>
>     Andrew
> .
Hi Andrew,
The PHY we test is RTL8211F, it supports 10 half. This problem actually is,
our board has MAC connected with PHY, when loopback test, packet flow is
MAC->PHY->MAC, it needs speed of MAC and PHY should be same when they work.

If PHY speed is unknown when PHY goes down, we will not set MAC speed in
adjust_link interface. In this case, we hope that PHY speed should not be
changed, as the old code of function genphy_loopback() before patch
"net: phy: genphy_loopback: add link speed configuration".

If PHY has never link, MAC speed has never be set in adjust_link interface,
yeah, in this case, MAC and PHY may has different speed, and they can not work.
I think we can accept this situation.

I think it is general problem if there is MAC connected with PHY.