netdev - Re: [PATCH net-next v12 09/15] net: stmmac: dwmac-loongson: Add phy

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Message-ID: <ZjnkuhmefxaySh1Z@shell.armlinux.org.uk>
Date: Tue, 7 May 2024 09:22:18 +0100
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Serge Semin <fancer.lancer@...il.com>
Cc: Yanteng Si <siyanteng@...ngson.cn>, andrew@...n.ch,
	hkallweit1@...il.com, peppe.cavallaro@...com,
	alexandre.torgue@...s.st.com, joabreu@...opsys.com,
	Jose.Abreu@...opsys.com, chenhuacai@...nel.org,
	guyinggang@...ngson.cn, netdev@...r.kernel.org,
	chris.chenfeiyang@...il.com, siyanteng01@...il.com
Subject: Re: [PATCH net-next v12 09/15] net: stmmac: dwmac-loongson: Add
 phy_interface for Loongson GMAC

On Sat, May 04, 2024 at 12:01:42AM +0300, Serge Semin wrote:
> Absolutely correct. Moreover AFAICS from the databooks the PCS module
> is only available for the DW GMACs with the TBI, RTBI and SGMII
> interfaces. So the STMMAC_PCS_RGMII PCS flag seems misleading. The only
> info about the link state that could be runtime detected on the MAC
> side is: link speed, duplex mode and link status. It's done by means
> of the RGMII in-band status signals. That's what is implemented in the
> dwmac1000_rgsmii() method.

... which you've now made me look at, look at the whole
pcs_link/pcs_speed/pcs_duplex and made me wonder why the hell stmmac
is making this so figgin difficult, messing with the carrier behind
phylink's back (which is a no-no), and why it needs to have separate
paths for this.

It doesn't.

Just because it doesn't have something called an official "PCS" does
not mean you _can't_ use a phylink_pcs to represent something that
has PCS-like properties - such as the RGMII in-band status which is
no different to what Cisco SGMII does.

This isn't something new... this is something that mvneta has
supported since before phylink was a thing, and so phylink had to
allow it as well.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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