netdev - Re: [PATCH RFC net-next] net: phylink: always config mac for (delayed) phy

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Message-ID: <Z31BRMay2QgcjX2R@shell.armlinux.org.uk>
Date: Tue, 7 Jan 2025 14:59:16 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Daniel Golle <daniel@...rotopia.org>
Cc: Eric Woudstra <ericwouds@...il.com>, Andrew Lunn <andrew@...n.ch>,
	Heiner Kallweit <hkallweit1@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	Frank Wunderlich <frank-w@...lic-files.de>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, netfilter-devel@...r.kernel.org,
	coreteam@...filter.org, bridge@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH RFC net-next] net: phylink: always config mac for
 (delayed) phy

On Tue, Jan 07, 2025 at 01:16:33PM +0000, Daniel Golle wrote:
> On Tue, Jan 07, 2025 at 12:47:14PM +0000, Russell King (Oracle) wrote:
> > ... but we don't see link-up reported by the PCS after the PHY comes
> > up. Why is that - I think that needs investigation before we proceed
> > to patch the issue, because that suggests the PCS isn't seeing
> > valid 2500base-X from the PHY.
> 
> The PCS doesn't support in-band status in 2500Base-X mode, or at least
> the implementation isn't compatible with those RealTek PHYs.

There is in-band for base-X, which involves 16-bit control words to
report the capabilities of either end (basically half/full duplex,
pause modes). Unlike SGMII, it doesn't contain any status bits for
link up, because that is irrelevant.

Link-up state in base-X modes comes from the PCS itself, whether the
PCS is in sync with the media, and whether it has valid format. This
has *nothing* to do with in-band.

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