linux-kernel - Re: [PATCH net-next v2 3/4] dt-bindings: net: Add RGMII internal delay for DP83869

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Message-ID: <20200520153631.GH652285@lunn.ch>
Date:   Wed, 20 May 2020 17:36:31 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Dan Murphy <dmurphy@...com>
Cc:     f.fainelli@...il.com, hkallweit1@...il.com, davem@...emloft.net,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH net-next v2 3/4] dt-bindings: net: Add RGMII internal
 delay for DP83869

> > Hi Dan
> > 
> > Having it required with PHY_INTERFACE_MODE_RGMII_ID or
> > PHY_INTERFACE_MODE_RGMII_RXID is pretty unusual. Normally these
> > properties are used to fine tune the delay, if the default of 2ns does
> > not work.
> 
> Also if the MAC phy-mode is configured with RGMII-ID and no internal delay
> values defined wouldn't that be counter intuitive?

Most PHYs don't allow the delay to be fine tuned. You just pass for
example PHY_INTERFACE_MODE_RGMII_ID to the PHY driver and it enables a
2ns delay. That is what people expect, and is documented.

Being able to tune the delay is an optional extra, which some PHYs
support, but that is always above and beyond
PHY_INTERFACE_MODE_RGMII_ID.

     Andrew