linux-kernel - Re: [PATCH net-next 1/2] dt-bindings: net: pcs: renesas,rzn1-miic: Add renesas,miic-phylink-active-low property

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Message-ID: <CA+V-a8vgJcJ+EsxSwQzQbprjqhxy-QS84=wE6co+D50wOOOweA@mail.gmail.com>
Date: Thu, 13 Nov 2025 18:53:41 +0000
From: "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: Clément Léger <clement.leger@...tlin.com>, 
	Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Heiner Kallweit <hkallweit1@...il.com>, Russell King <linux@...linux.org.uk>, 
	Geert Uytterhoeven <geert+renesas@...der.be>, Magnus Damm <magnus.damm@...il.com>, 
	linux-renesas-soc@...r.kernel.org, netdev@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Biju Das <biju.das.jz@...renesas.com>, 
	Fabrizio Castro <fabrizio.castro.jz@...esas.com>, 
	Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [PATCH net-next 1/2] dt-bindings: net: pcs: renesas,rzn1-miic:
 Add renesas,miic-phylink-active-low property

Hi Andrew,

On Wed, Nov 12, 2025 at 8:58 PM Andrew Lunn <andrew@...n.ch> wrote:
>
> On Wed, Nov 12, 2025 at 08:19:36PM +0000, Prabhakar wrote:
> > From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> >
> > Add the boolean DT property `renesas,miic-phylink-active-low` to the RZN1
> > MIIC binding schema. This property allows configuring the active level
> > of the PHY-link signals used by the Switch, EtherCAT, and SERCOS III
> > interfaces.
> >
> > The signal polarity is controlled by fields in the MIIC_PHYLINK register:
> >   - SWLNK[3:0]: configures the Switch interface link signal level
> >       0 - Active High
> >       1 - Active Low
> >   - CATLNK[6:4]: configures the EtherCAT interface link signal level
> >       0 - Active Low
> >       1 - Active High
> >   - S3LNK[9:8]: configures the SERCOS III interface link signal level
> >       0 - Active Low
> >       1 - Active High
> >
> > When the `renesas,miic-phylink-active-low` property is present, the
> > PHY-link signal is configured as active-low. When omitted, the signal
> > defaults to active-high.
>
> Sorry, but i asked in a previous version, what is phy-link? You still
> don't explain what this signal is. phylib/phylink tells you about the
> link state, if there is a link partner, what link speed has been
> negotiated, duplex, pause etc. What does this signal indicate?
>

                                   +----> Ethernet Switch -------->
GMAC (Synopsys IP)
                                    |
                                    |
MII Converter ----------+
                                    |
                                   +----> EtherCAT Slave Controller
                                   |
                                   |
                                   +----> SERCOS Controller

Each of these IPs has its own link status pin as an input to the SoC:

SWITCH_MII_LINK: Switch PHY link status input
S3_MII_LINKP: SERCOS III link status from PHY
CAT_MII_LINK: EtherCAT link status from PHY

The above architecture is for the RZ/N1 SoC. For RZ/T2H SoC we dont
have a SERCOS Controller. So in the case of RZ/T2H EVK the
SWITCH_MII_LINK status pin is connected to the LED1 of VSC8541 PHY.

The PHYLNK register [0] (section 10.2.5 page 763) allows control of
the active level of the link.
0: High active (Default)
1: Active Low

For example the SWITCH requires link-up to be reported to the switch
via the SWITCH_MII_LINK input pin.

[0] https://www.renesas.com/en/document/mah/rzn1d-group-rzn1s-group-rzn1l-group-users-manual-r-engine-and-ethernet-peripherals?r=1054561

Cheers,
Prabhakar