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

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Date:   Wed, 11 Aug 2021 23:14:17 +0530
From:   Prasanna Vengateshan <prasanna.vengateshan@...rochip.com>
To:     Andrew Lunn <andrew@...n.ch>, Vladimir Oltean <olteanv@...il.com>
CC:     "Russell King (Oracle)" <linux@...linux.org.uk>,
        <netdev@...r.kernel.org>, <robh+dt@...nel.org>,
        <UNGLinuxDriver@...rochip.com>, <Woojung.Huh@...rochip.com>,
        <hkallweit1@...il.com>, <davem@...emloft.net>, <kuba@...nel.org>,
        <linux-kernel@...r.kernel.org>, <vivien.didelot@...il.com>,
        <f.fainelli@...il.com>, <devicetree@...r.kernel.org>
Subject: Re: [PATCH v3 net-next 05/10] net: dsa: microchip: add DSA support
 for microchip lan937x

On Sat, 2021-08-07 at 17:40 +0200, Andrew Lunn wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the
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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?