netdev - Re: [PATCH] sfc: Export fibre-specific link modes for 1/10G

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Date:   Tue, 19 Oct 2021 20:55:25 +0200
From:   Erik Ekman <erik@...o.se>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Edward Cree <ecree.xilinx@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org
Subject: Re: [PATCH] sfc: Export fibre-specific link modes for 1/10G

On Tue, 19 Oct 2021 at 20:27, Andrew Lunn <andrew@...n.ch> wrote:
>
> On Tue, Oct 19, 2021 at 07:34:16PM +0200, Erik Ekman wrote:
> > On Tue, 19 Oct 2021 at 17:53, Martin Habets <habetsm.xilinx@...il.com> wrote:
> > >
> > > On Tue, Oct 19, 2021 at 05:31:52PM +0200, Andrew Lunn wrote:
> > > > On Mon, Oct 18, 2021 at 08:37:08PM +0200, Erik Ekman wrote:
> > > > > These modes were added to ethtool.h in 5711a98221443 ("net: ethtool: add support
> > > > > for 1000BaseX and missing 10G link modes") back in 2016.
> > > > >
> > > > > Only setting CR mode for 10G, similar to how 25/40/50/100G modes are set up.
> > > > >
> > > > > Tested using SFN5122F-R7 (with 2 SFP+ ports) and a 1000BASE-BX10 SFP module.
> > > >
> > > > Did you test with a Copper SFP modules?
> > > >
> >
> > I have tested it with a copper SFP PHY at 1G and that works fine.
>
> Meaning ethtool returns 1000BaseT_FULL? Does the SFP also support
> 10/100? Does ethtool list 10BaseT_Half, 10BaseT_Full, etc.
>

The supported modes do not change based on the module used.  From the
code it looks to only be based on the phy capability bits
(MC_CMD_PHY_CAP_1000FDX_LBN, MC_CMD_PHY_CAP_10000FDX_LBN).
The copper SFP does not link at 100Mbps, only at 1Gbps (from my testing).

>From the 'Solarflare Server Adapter User Guide': "SFP 1000BASE‐T
module, Autonegotiation: No, Speed:  1G, Comment: These modules
support only 1G and will not link up at 100Mbps"
10G SFP+ Base-T modules are not mentioned, maybe they did not exist
back then. Do you think the 1000BaseT_Full should be used because of
this?

Reading the user guide further I see lists of supported SFP+ -LR and
-SR modules as well as QSFP+ SR4 modules so I am planning to add them.

/Erik