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

[Andrew Lunn <andrew@lunn.ch>]

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 <markus.stockhausen@gmx.de>

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

    Andrew