netdev - RE: [PATCH net-next 1/3] dt-bindings: net: tja11xx: use reverse-mode to instead of rmii-refclk-in

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Message-ID:
 <PAXPR04MB85108770DAF2E69C969FD24288812@PAXPR04MB8510.eurprd04.prod.outlook.com>
Date: Fri, 16 Aug 2024 01:39:06 +0000
From: Wei Fang <wei.fang@....com>
To: Andrew Lunn <andrew@...n.ch>
CC: "davem@...emloft.net" <davem@...emloft.net>, "edumazet@...gle.com"
	<edumazet@...gle.com>, "kuba@...nel.org" <kuba@...nel.org>,
	"pabeni@...hat.com" <pabeni@...hat.com>, "robh@...nel.org" <robh@...nel.org>,
	"krzk+dt@...nel.org" <krzk+dt@...nel.org>, "conor+dt@...nel.org"
	<conor+dt@...nel.org>, "f.fainelli@...il.com" <f.fainelli@...il.com>,
	"hkallweit1@...il.com" <hkallweit1@...il.com>, "linux@...linux.org.uk"
	<linux@...linux.org.uk>, "Andrei Botila (OSS)" <andrei.botila@....nxp.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>
Subject: RE: [PATCH net-next 1/3] dt-bindings: net: tja11xx: use reverse-mode
 to instead of rmii-refclk-in

> -----Original Message-----
> From: Andrew Lunn <andrew@...n.ch>
> Sent: 2024年8月15日 22:33
> To: Wei Fang <wei.fang@....com>
> Cc: davem@...emloft.net; edumazet@...gle.com; kuba@...nel.org;
> pabeni@...hat.com; robh@...nel.org; krzk+dt@...nel.org;
> conor+dt@...nel.org; f.fainelli@...il.com; hkallweit1@...il.com;
> linux@...linux.org.uk; Andrei Botila (OSS) <andrei.botila@....nxp.com>;
> netdev@...r.kernel.org; devicetree@...r.kernel.org;
> linux-kernel@...r.kernel.org
> Subject: Re: [PATCH net-next 1/3] dt-bindings: net: tja11xx: use reverse-mode
> to instead of rmii-refclk-in
> 
> On Thu, Aug 15, 2024 at 01:51:24PM +0800, Wei Fang wrote:
> > Per the MII and RMII specifications, for the standard RMII mode, the
> > REF_CLK is sourced from MAC to PHY or from an external source.
> > For the standard MII mode, the RX_CLK and TX_CLK are both sourced by
> > the PHY. But for TJA11xx PHYs, they support reverse mode, that is, for
> > revRMII mode, the REF_CLK is output, and for revMII mode, the TX_CLK
> > and RX_CLK are inputs to the PHY.
> > Previously the "nxp,rmii-refclk-in" was added to indicate that in RMII
> > mode, if this property present, REF_CLK is input to the PHY, otherwise
> > it is output. This seems inappropriate now. Firstly, for the standard
> > RMII mode, REF_CLK is originally input, and there is no need to add
> > the "nxp,rmii-refclk-in" property to indicate that REF_CLK is input.
> > Secondly, this property is not generic for TJA PHYs, because it cannot
> > cover the settings of TX_CLK and RX_CLK in MII mode. Therefore, add
> > new property "nxp,reverse-mode" to instead of the "nxp,rmii-refclk-in"
> > property.
> 
> Please could you add some justification why using
> PHY_INTERFACE_MODE_REVRMII is not possible.
> 

According to the commit message c858d436be8b ("net: phy: introduce
PHY_INTERFACE_MODE_REVRMII"), my understanding is that
PHY_INTERFACE_MODE_REVRMII and PHY_INTERFACE_MODE_REVMII
are used for MAC to MAC connections, which means the MAC behaves
link an RMII/MII PHY. For the MAC to PHY connection, I think these two
macros are not applicable.
Currently PHY_INTERFACE_MODE_REVMII is used in both TJA11xx drivers,
and if my understanding is correct I think they will need to be removed in
the future.