Re: [PATCH net-next] Revert "net: ethernet: ti: am65-cpsw: fixup PHY mode for fixed RGMII TX delay"

[Andrew Lunn]

> I can confirm that the undocumented/reserved bit switches the MAC-side TX delay
> on and off on the J722S/AM67A.

Thanks.

> I have not checked if there is anything wrong with the undelayed
> mode that might explain why TI doesn't want to support it, but
> traffic appears to flow through the interface without issue if I
> disable the MAC-side and enable the PHY-side delay.

I cannot say this is true for TI, but i've often had vendors say that
they want the MAC to do the delay so you can use a PHY which does not
implement delays. However, every single RGMII PHY driver in Linux
supports all four RGMII modes. So it is a bit of a pointless argument.

And MAC vendors want to make full use of the hardware they have, so
naturally want to do the delay in the MAC because they can.

TI is a bit unusual in this, in that they force the delay on. So that
adds a little bit of weight towards maybe there being a design issue
with it turned off.

	Andrew