linux-kernel - RE: [PATCH net-next v2 3/3] phy: mscc: Add support for VSC8531

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Date:   Wed, 26 Apr 2023 17:39:43 +0000
From:   "Katakam, Harini" <harini.katakam@....com>
To:     Vladimir Oltean <vladimir.oltean@....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

Hi Vladimir,

> -----Original Message-----
> From: Vladimir Oltean <vladimir.oltean@....com>
> Sent: Wednesday, April 26, 2023 7:49 PM
> To: Katakam, Harini <harini.katakam@....com>
> Cc: robh+dt@...nel.org; andrew@...n.ch; hkallweit1@...il.com;
> linux@...linux.org.uk; davem@...emloft.net; kuba@...nel.org;
> edumazet@...gle.com; pabeni@...hat.com; wsa+renesas@...g-
> engineering.com; krzysztof.kozlowski+dt@...aro.org;
> simon.horman@...igine.com; netdev@...r.kernel.org;
> devicetree@...r.kernel.org; linux-kernel@...r.kernel.org;
> 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.

Thanks, yes I noticed the difference here and also in older PHY drivers that
used custom properties (see dp83867 which is what I originally aligned it to).
But the table you mentioned above makes sense; I'll re-spin accordingly.

> My interpretation was based on the wording from the dt-bindings document,
> which seems to suggest that rx-internal-delay-ps takes precedence.

OK I understand.

Regards,
Harini