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:
 <PAXPR04MB8510FBC63D4C924B13F26BD988812@PAXPR04MB8510.eurprd04.prod.outlook.com>
Date: Fri, 16 Aug 2024 02:57:44 +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16日 10:33
> 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
> 
> > 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.
> 
> In MAC to MAC connections, REVRMII means that end plays the role of a
> PHY, even though it is a MAC.
> 
> What is actually happening when you use these properties/register
> setting on the PHY?  It is playing the role of a MAC? In order to have
> a working link, do you need to tell the MAC to play the role of the
> PHY?
> 
Based on the TJA data sheet, like TJA1103/TJA1104, if the reverse mode
is set. If XMII_MODE is set to MII, the device operates in revMII mode
(TXCLK and RXCLK are input). If XMII_MODE is set to RMII, the device
operates in revRMII mode (REF_CLK is output). So it's just that the input
and output directions of xx_CLK are reversed.
we don't need to tell the MAC to play the role of the PHY, in our case, we
just need the PHY to provide the reference clock in RMII mode.