How do 'miibus' PHY devices handle target HW differences?

[Greg Huckriede]

I'm using the 'ffec' driver (in 12.1-RELEASE) but the target has the
following Flattened Device Tree (FDT) setting for the 'ethernet' device.

phy-mode = "rgmii-txid";

This indicates that the PHY 'athphy' needs to provide the tx clock delay
on the RGMII. This is configurable in the 'atphy' device. The 'atphy'
device could get this setting from the FDT (like the 'vscphy' driver does).

How is this supposed to work?

It seems the FDT could be read during attach for all PHYs, and populate
the settings if present. Also how do non-FDT targets deal with HW
differences like this?

Regards,
Greg Huckriede