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

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Date:   Wed, 20 May 2020 09:03:52 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Dan Murphy <dmurphy@...com>, Andrew Lunn <andrew@...n.ch>
Cc:     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



On 5/20/2020 8:56 AM, Dan Murphy wrote:
> Andrew
> 
> On 5/20/20 10:36 AM, Andrew Lunn wrote:
>>>> 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.
> 
> I am interested in knowing where that is documented.  I want to RTM I
> grepped for a few different words but came up empty
> 
> Since this is a tuneable phy we need to program the ID.  2ns is the
> default value
> 
> Maybe I can change it from Required to Configurable or Used.

I do not think this is properly documented, it is an established
practice, but it should be clearly documented somewhere, I do not know
whether that belongs in the PHY Device Tree binding or if this belongs
to the PHY documentation.
-- 
Florian