netdev - Re: [PATCH net-next v2 3/3] phy: mscc: Add support for VSC8531

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Date:   Wed, 26 Apr 2023 17:18:31 +0300
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     "Katakam, Harini" <harini.katakam@....com>
Cc:     "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "andrew@...n.ch" <andrew@...n.ch>,
        "hkallweit1@...il.com" <hkallweit1@...il.com>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "wsa+renesas@...g-engineering.com" <wsa+renesas@...g-engineering.com>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "simon.horman@...igine.com" <simon.horman@...igine.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "harinikatakamlinux@...il.com" <harinikatakamlinux@...il.com>,
        "Simek, Michal" <michal.simek@....com>,
        "Pandey, Radhey Shyam" <radhey.shyam.pandey@....com>
Subject: Re: [PATCH net-next v2 3/3] phy: mscc: Add support for VSC8531_02
 with RGMII tuning

On Wed, Apr 26, 2023 at 12:21:47PM +0000, Katakam, Harini wrote:
> Thanks for the review.
> The intention is to have the following precedence (I'll rephrase the commit if required)
> -> If phy-mode is rgmii, current behavior persists for all devices
> -> If phy-mode is rgmii-id/rgmii-rxid/rgmii-txid, current behavior persists for all devices
> (i.e. delay of RGMII_CLK_DELAY_2_0_NS)
> -> If phy-mode is rgmii-id/rgmii-rxid/rgmii-txid AND rx-internal-delay-ps/tx-internal-delay-ps
> is defined, then the value from DT is considered instead of 2ns. (NOT irrespective of phy-mode)
> 
> I'm checking the phy drivers that use phy_get_internal_delay and the description phy-mode
> in ethernet-controller.yaml and rx/tx-internal-delay-ps in ethernet-phy.yaml. It does look like
> the above is allowed. Please do let me know otherwise.

I understood what your intention was. What I meant was:

 phy-mode                       rgmii                          rgmii-rxid/rgmii-id
 --------------------------------------------------------------------------------------------
 rx-internal-delay-ps absent    0.2 ns                         2 ns
 rx-internal-delay-ps present   follow rx-internal-delay-ps    follow rx-internal-delay-ps

I agree with Andrew that probably there isn't consistency among PHY
drivers for this interpretation - see dp83822 vs intel-xway for example.
My interpretation was based on the wording from the dt-bindings document,
which seems to suggest that rx-internal-delay-ps takes precedence.