Re: [PATCH net-next v3 0/5] net: stmmac: Add support for Allwinner A733 GMAC210

[Andrew Lunn <andrew@lunn.ch>]

> > You need to differentiate between small fine tuning delays, and the
> > 2ns delay required by the RGMII standard. If the MAC is just doing
> > fine tuning, you need to still pass PHY_INTERFACE_MODE_RGMII_ID so the
> > PHY adds the 2ns delay. If the MAC is adding a big delay, you need to
> > pass PHY_INTERFACE_MODE_RGMII to the PHY.
> 
> The PHY is one concern but the series here does not really address this
> topic. DTS and board specific concerns will come later.

They are all interconnected. When phy-mode says 'rgmii-id', it is the
MAC/PHY pair which needs to decide who adds the delay. If the phy-mode
is 'na', how does the MAC know it needs to use RGMII, not MII, as you
said.

We need to keep the big picture in mind, otherwise you could go down a
dead end, and a dead end which makes backwards compatibility really
messy.

> It is really just the MAC. So, how does the MAC is supposed to
> make the decision to amend the PHY mode ? is there a threshold you'd
> like to recommend for this differentiation ? 

This is the first time we have had this condition. So it has not
really been thought about too much. Maybe 1ns. That is the middle of
the 2ns required by RGMII.

> I'll try to reach out, just in case. I have the schematics but without
> the PHY doc, it does not help much.

From that i assume you missed the other emails. Somebody from ARM give
a link to the data sheet. It documents the strapping. Search for the
patch adding the PHY driver, it is in that thread.

	Andrew