netdev - RE: [PATCH net] r8169: fix rtl8168h wol fail

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Date:   Fri, 13 Jan 2023 16:23:45 +0000
From:   Hau <hau@...ltek.com>
To:     Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        nic_swsd <nic_swsd@...ltek.com>
Subject: RE: [PATCH net] r8169: fix rtl8168h wol fail

> > >>> In this application(rtl8168h + rtl8211fs) it also supports 100Mbps
> > >>> fiber
> > >> module.
> > >>
> > >> Does RTL8211FS advertise 100Mbps and 1Gbps on the UTP/MDI side in
> > >> case of a 100Mbps fiber module?
> > > Yes.
> > >
> > I think in this case internal PHY and RTL8211FS would negotiate 1Gbps,
> > not matching the speed of the 100Mbps fiber module.
> > How does this work?

My mistake. With 100Mbps fiber module RTL8211FS will only advertise 100Mbps
on the UTP/MDI side. With 1Gbps fiber module it will advertise both 100Mbps and
1Gbps. So issue will only happen with 1Gbps fiber module.

> Fibre line side has no autoneg. Both ends need to be using the same speed,
> or the SERDES does not synchronise and does not establish link.
> 
> You can ask the SFP module what baud rate it supports, and then use
> anything up to that baud rate. I've got systems where the SFP is fast enough
> to support a 2.5Gbps link, so the MAC indicates both 2.5G and 1G, defaults to
> 2.5G, and fails to connect to a 1G link peer. You need to use ethtool to force
> it to the lower speed before the link works.
> 
> But from what i understand, you cannot use a 1000Base-X SFP, set the MAC
> to 100Mbps, and expect it to connect to a 100Base-FX SFP. So for me, the
> RTL8211FS should not be advertise 100Mbps and 1Gbps, it needs to talk to
> the SFP figure out exactly what it is, and only advertise the one mode which
> is supported.

It is the RTL8211FS firmware bug. This patch is for workaround this issue.

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