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

From: "Russell King (Oracle)" <[email-masked]>
Date: Tue, 25 Jul 2023 10:58:25 +0100

On Tue, Jul 25, 2023 at 05:50:36PM +0800, Jiawen Wu wrote:
> 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

This makes no sense. a PHY on a RJ45 SFP module is just the same as a
PHY integrated into a board with the MAC.

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