Re: [PATCH net-next v1 1/1] Documentation: networking: add detailed guide on Ethernet flow control configuration

[Russell King (Oracle)]

On Thu, Jul 17, 2025 at 12:37:02PM +0200, Oleksij Rempel wrote:
> +Changing the Settings
> +---------------------
> +Use `ethtool -A <interface>` to change the settings.
> +
> +.. code-block:: bash
> +
> +  # Enable RX and TX pause, with autonegotiation
> +  ethtool -A eth0 autoneg on rx on tx on
> +
> +  # Force RX pause on, TX pause off, without autonegotiation
> +  ethtool -A eth0 autoneg off rx on tx off
> +
> +**Key Configuration Concepts**:
> +
> +* **Autonegotiation Mode**: The recommended mode. The driver programs the PHY
> +    to *advertise* the `rx` and `tx` capabilities. The final active state is
> +    determined by what both sides of the link agree on.

I'm not sure one cal call this "recommended mode", because it doesn't.
If one specifies tx=0 rx=1, one would expect that the "recommend mode"
would be tx=0 and rx=1, but if the link partner supports symmetric
pause, you actually end up with tx=1 and rx=1. If the link partner
supports only asymmetric, then you end up with tx=0 rx=1 as requested.

Perversely, if you specify tx=1 rx=1, then if the remote supports only
asymmetric, you end up with everything disabled. Only tx=1 rx=1 is
supported in this configuration, you can't end up with anything else.

Basically, I don't think calling it "recommended" works.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!