linux-kernel - Re: [PATCH] net: phy: mscc: enable MAC SerDes autonegotiation

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Date:   Sun, 6 Feb 2022 17:18:20 +0000
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Raag Jadav <raagjadav@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Steen Hegelund <steen.hegelund@...rochip.com>,
        Bjarni Jonasson <bjarni.jonasson@...rochip.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: phy: mscc: enable MAC SerDes autonegotiation

On Sun, Feb 06, 2022 at 10:42:34PM +0530, Raag Jadav wrote:
> Once the PHY auto-negotiates parameters such as speed and duplex mode
> with its link partner over the copper link as per IEEE 802.3 Clause 27,
> the link partner’s capabilities are then transferred by PHY to MAC
> over 1000BASE-X or SGMII link using the auto-negotiation functionality
> defined in IEEE 802.3z Clause 37.

This is slightly incorrect. 1000BASE-X is only capable of operating at
gigabit speed, not at 100M or 10M.

The PHY _might_ signal the copper side pause resolution via the
1000BASE-X negotiation word, and even rarer would be whether operating
at 1G FD or 1G HD.

Out of the two, only SGMII is capable of operating at 1G, 100M and 10M,
FD or HD. No pause resolution is passed. SGMII is not an 802.3 defined
protocol, it's an adaption of 1000BASE-X by Cisco.

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