netdev - RE: [PATCH net-next 4/7] net: pcs: xpcs: adapt Wangxun NICs for SGMII mode

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Date: Tue, 25 Jul 2023 17:50:36 +0800
From: Jiawen Wu <jiawenwu@...stnetic.com>
To: "'Russell King \(Oracle\)'" <linux@...linux.org.uk>
Cc: <netdev@...r.kernel.org>,
	<andrew@...n.ch>,
	<hkallweit1@...il.com>,
	<Jose.Abreu@...opsys.com>,
	<mengyuanlou@...-swift.com>
Subject: RE: [PATCH net-next 4/7] net: pcs: xpcs: adapt Wangxun NICs for SGMII mode

On Tuesday, July 25, 2023 3:49 PM, Russell King (Oracle) wrote:
> On Tue, Jul 25, 2023 at 10:05:05AM +0800, Jiawen Wu wrote:
> > On Monday, July 24, 2023 6:35 PM, Russell King (Oracle) wrote:
> > > On Mon, Jul 24, 2023 at 06:23:38PM +0800, Jiawen Wu wrote:
> > > > Wangxun NICs support the connection with SFP to RJ45 module. In this case,
> > > > PCS need to be configured in SGMII mode.
> > > >
> > > > Accroding to chapter 6.11.1 "SGMII Auto-Negitiation" of DesignWare Cores
> > > > Ethernet PCS (version 3.20a) and custom design manual, do the following
> > > > configuration when the interface mode is SGMII.
> > > >
> > > > 1. program VR_MII_AN_CTRL bit(3) [TX_CONFIG] = 1b (PHY side SGMII)
> > > > 2. program VR_MII_AN_CTRL bit(8) [MII_CTRL] = 1b (8-bit MII)
> > > > 3. program VR_MII_DIG_CTRL1 bit(0) [PHY_MODE_CTRL] = 1b
> > >
> > > I'm confused by "PHY side SGMII" - what does this mean for the
> > > transmitted 16-bit configuration word? Does it mean that _this_ side
> > > is acting as if it were a PHY?
> >
> > I'm not sure, because the datasheet doesn't explicitly describe it. In this
> > case, the PHY is integrated in the SFP to RJ45 module. From my point of
> > view, TX control occurs on the PHY side. So program it as PHY side SGMII.
> 
> Let me ask the question a different way. Would you use "PHY side SGMII"
> if the PHY was directly connected to the PCS with SGMII?

The information obtained from the IC designer is that "PHY/MAC side SGMII"
is configured by experimentation. For these different kinds of NICs:
1) fiber + SFP-RJ45 module: PHY side SGMII
2) copper (pcs + external PHY): MAC side SGMII
3) backplane: PHY side SGMII

Backplane is not supported in the driver yet. If consider the "side" as "acting"
point, case 1 (this patch implement) seems more like "MAC side SGMII". But
in practice, it won't work.