Re: [PATCH net-next v4 0/4] usbnet: speed reporting for devices without MDIO

On Mon, Apr 05, 2021 at 04:13:40PM -0700, Grant Grundler wrote:

This series introduces support for USB network devices that report
speed as a part of their protocol, not emulating an MII to be accessed
over MDIO.

v2: rebased on recent upstream changes
v3: incorporated hints on naming and comments
v4: fix misplaced hunks; reword some commit messages;
    add same change for cdc_ether
v4-repost: added "net-next" to subject and Andrew Lunn's Reviewed-by

I'm reposting Oliver Neukum's [off-list ref] patch series with
fix ups for "misplaced hunks" (landed in the wrong patches).
Please fixup the "author" if "git am" fails to attribute the
patches 1-3 (of 4) to Oliver.

I've tested v4 series with "5.12-rc3+" kernel on Intel NUC6i5SYB
and + Sabrent NT-S25G. Google Pixelbook Go (chromeos-4.4 kernel)
+ Alpha Network AUE2500C were connected directly to the NT-S25G
to get 2.5Gbps link rate:
# ethtool enx002427880815
Settings for enx002427880815:
        Supported ports: [  ]
        Supported link modes:   Not reported
        Supported pause frame use: No
        Supports auto-negotiation: No
        Supported FEC modes: Not reported
        Advertised link modes:  Not reported
        Advertised pause frame use: No
        Advertised auto-negotiation: No
        Advertised FEC modes: Not reported
        Speed: 2500Mb/s
        Duplex: Half
        Auto-negotiation: off
        Port: Twisted Pair
        PHYAD: 0
        Transceiver: internal
        MDI-X: Unknown
        Current message level: 0x00000007 (7)
                               drv probe link
        Link detected: yes


"Duplex" is a lie since we get no information about it.

You can ask the PHY. At least those using mii or phylib.  If you are
using mii, then mii_ethtool_get_link_ksettings() should set it
correctly. If you are using phylib, phy_ethtool_get_link_ksettings()
will correctly set it. If you are not using either of these, you are
on your own.

Speed: 2500Mb/s and Duplex: Half is very unlikely. You really only
ever see 10 Half and occasionally 100 Half. Anything above that will
be full duplex.

It is probably best to admit the truth and use DUPLEX_UNKNOWN.

I expect "Auto-Negotiation" is always true for cdc_ncm and
cdc_ether devices and perhaps someone knows offhand how
to have ethtool report "true" instead.

ethtool_link_ksettings contains three bitmaps:

supported: The capabilities of this device.
advertising: What this device is telling the link peer it can do.
lp_advertising: What the link peer is telling us it can do.

So to get Supports auto-negotiation to be true you need to set bit
ETHTOOL_LINK_MODE_Autoneg_BIT in supported.
For Advertised auto-negotiation: you need to set the same bit in
advertising. 

Auto-negotiation: off is i think from base.autoneg.

	Andrew