Re: [PATCH 2/2] net: ethernet: stmicro: stmmac: dwmac-rk: Add rv1126 support

[Andrew Lunn]

On Mon, Aug 29, 2022 at 06:50:42AM +0000, Anand Moon wrote:
> Rockchip RV1126 has GMAC 10/100/1000M ethernet controller
> via RGMII and RMII interfaces are configured via M0 and M1 pinmux.
> 
> This patch adds rv1126 support by adding delay lines of M0 and M1
> simultaneously.

What does 'delay lines' mean with respect to RGMII?

The RGMII signals need a 2ns delay between the clock and the data
lines. There are three places this can happen:

1) In the PHY
2) Extra long lines on the PCB
3) In the MAC

Generally, 1) is used, and controlled via phy-mode. A value of
PHY_INTERFACE_MODE_RGMII_ID passed to the PHY driver means it will add
these delays.

You don't want both the MAC and the PHY adding delays.

    Andrew