Re: [PATCH v3 net-next 05/10] net: dsa: microchip: add DSA support for microchip lan937x

Prasanna Vengateshan
2021-08-11T17:44:27Z

On Sat, 2021-08-07 at 17:40 +0200, Andrew Lunn wrote:
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> > I am not even clear what is the expected canonical behavior for a MAC
> > driver. It parses rx-internal-delay-ps and tx-internal-delay-ps, and
> > then what?
>
> So best practices are based around a MAC-PHY link. phy-mode is passed
> to the PHY, and the MAC does not act upon it. MAC rx-internal-delay-ps
> and tx-internal-delay-ps can be used to fine tune the link. You can
> use them to add and sometimes subtract small amounts of delay.
>
> > It treats all "rgmii*" phy-mode strings identically? Or is it an
> > error to have "rgmii-rxid" for phy-mode and non-zero
> > rx-internal-delay-ps?
>
> I would say the first is correct, the second statement is false. You
> should always be able to fine tune the link, independent of the PHY
> mode.
>
> We also have to consider the case when the PHY is not actually able to
> implement the delay. It hopefully returns -EOPNOTSUPP for anything
> other than "rgmii". You can then put the full 2ns delay into
> tx-internal-delay-ps nd rx-internal-delay-ps.

I hope that using "*-internal-delay-ps" for Mac would be the right option.
Shall i include these changes as we discussed in next revision of the patch?