linux-kernel - Re: [PATCH 2/5] dt-bindings: net: add schema for NXP S32CC dwmac glue driver

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Date:   Fri, 4 Nov 2022 19:39:43 +0800
From:   Chester Lin <clin@...e.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Andreas Färber <afaerber@...e.de>,
        Rob Herring <robh@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Jan Petrous <jan.petrous@....com>, netdev@...r.kernel.org,
        s32@....com, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Matthias Brugger <mbrugger@...e.com>,
        Chester Lin <clin@...e.com>
Subject: Re: [PATCH 2/5] dt-bindings: net: add schema for NXP S32CC dwmac
 glue driver

Hi Andrew and Andreas,

On Thu, Nov 03, 2022 at 11:05:30PM +0100, Andrew Lunn wrote:
> > > > +      - description: Main GMAC clock
> > > > +      - description: Peripheral registers clock
> > > > +      - description: Transmit SGMII clock
> > > > +      - description: Transmit RGMII clock
> > > > +      - description: Transmit RMII clock
> > > > +      - description: Transmit MII clock
> > > > +      - description: Receive SGMII clock
> > > > +      - description: Receive RGMII clock
> > > > +      - description: Receive RMII clock
> > > > +      - description: Receive MII clock
> > > > +      - description:
> > > > +          PTP reference clock. This clock is used for programming the
> > > > +          Timestamp Addend Register. If not passed then the system
> > > > +          clock will be used.
> 
> > Not clear to me has been whether the PHY mode can be switched at runtime
> > (like DPAA2 on Layerscape allows for SFPs) or whether this is fixed by board
> > design.
> 
> Does the hardware support 1000BaseX? Often the hardware implementing
> SGMII can also do 1000BaseX, since SGMII is an extended/hacked up
> 1000BaseX.
> 
> If you have an SFP connected to the SERDES, a fibre module will want
> 1000BaseX and a copper module will want SGMII. phylink will tell you
> what phy-mode you need to use depending on what module is in the
> socket. This however might be a mute point, since both of these are
> probably using the SGMII clocks.
> 
> Of the other MII modes listed, it is very unlikely a runtime swap will
> occur.
> 
> 	Andrew

Here I just focus on GMAC since there are other LAN interfaces that S32 family
uses [e.g. PFE]. According to the public GMACSUBSYS ref manual rev2[1] provided
on NXP website, theoretically GMAC can run SGMII in 1000Mbps and 2500Mbps so I
assume that supporting 1000BASE-X could be achievable. I'm not sure if any S32
board variant might have SFP ports but RJ-45 [1000BASE-T] should be the major
type used on S32G-EVB and S32G-RDB2.

@NXP, please feel free to correct me if anything wrong.

Thanks,
Chester

[1] https://www.nxp.com/webapp/Download?colCode=GMACSUBSYSRM -> Membership
subscription is required although it's free IIRC.