Re: [PATCH net-next v4 5/5] net: mdio: realtek-rtl9300: support non-default clock frequencies

On Sat, Sep 12, 2026 at 03:04:51PM +0200, Markus Stockhausen wrote:

The Ethernet MDIO controllers in Realtek Otto switches use an MDC clock
frequency of 2.5 MHz by default. Hardware configuration fields allow the
following frequencies to be selected:

- RTL838x: 2.5 MHz or 10 MHz
- RTL839x, RTL930x and RTL931x: 1.25 MHz, 2.5 MHz or 5 MHz

Add support for configuring the MDC frequency through the
clock-frequency property of each MDIO bus node. Lower frequencies can
simplify protocol analysis with a logic analyzer, while higher
frequencies reduce MDIO transaction times during normal operation.

Program the frequency selector during every probe. If clock-frequency is
absent, select the defined default of 2.5 MHz. This matches the
configuration observed with a protocol analyzer under the stock firmware
or after issuing "rtk network on" in the bootloader.

RTL839x is an exception because both MDIO buses share a single frequency
field. Use an explicitly specified frequency as the shared frequency and
let buses without the property inherit it. Use the 2.5 MHz default if
neither bus specifies a frequency. Reject conflicting explicit
frequencies because the hardware cannot configure them independently.

Signed-off-by: Markus Stockhausen <redacted>

Reviewed-by: Andrew Lunn <andrew@lunn.ch>

    Andrew