Re: [PATCH v2] arm64: dts: rockchip: Adjust RGMII TXD/RXD delays for the Rock Pi E

[Adrian Kossmann <adrian.kossmann@posteo.de>]

Hi Andrew,

> rgmii means the PCB provides the delay. I doubt that is the
> case.

Yes, however, to my understanding, there are two kinds of delays that
influence RGMII timing: Delays that are added onto the clock signal 
(TXC/RXC) and delays added to the data signal (TXD/RXD) by the GMAC.
The link provided by you describes delays that are either introduced by 
longer clock traces  on the PCB (rgmii phy-mode) or by programmable clock delays 
(rgmii-id phy-mode). Delays for TXD timing and RXD timing are described in [1] 
and are implemented by the Rockchip Ethernet driver which is bound to node 
gmac2io according to [2]. The example DT binding in [1] as well as other 
mainline DTS of devices that use the RK3328 seem to adjust RGMII timing 
via TXD and RXD delays and setting phy-mode to rgmii, despite having 
programmable TXC/RXC delays, at least according to the technical 
manual of the RK3328. So, in this case this may be an exception
from the usual convention that any RGMII phy mode other than 
'rgmii-id' is probably wrong.

Of course, I may have overlooked something or misunderstood, and I 
would appreciate further guidance in this case.

[1] https://www.kernel.org/doc/Documentation/devicetree/bindings/net/rockchip-dwmac.txt
[2] https://git.kernel.org/pub/scm/linux/kernel/git/mmind/linux-rockchip.git/tree/arch/arm64/boot/dts/rockchip/rk3328.dtsi#n982


      Adrian