netdev - Re: [PATCH v2 net 6/6] net: enetc: force the RGMII speed and duplex instead of operating in inband mode

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Message-ID: <20210225171415.GU1463@shell.armlinux.org.uk>
Date:   Thu, 25 Feb 2021 17:14:15 +0000
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        Michael Walle <michael@...le.cc>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandru Marginean <alexandru.marginean@....com>,
        Vladimir Oltean <vladimir.oltean@....com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>
Subject: Re: [PATCH v2 net 6/6] net: enetc: force the RGMII speed and duplex
 instead of operating in inband mode

On Thu, Feb 25, 2021 at 02:18:35PM +0200, Vladimir Oltean wrote:
> From: Vladimir Oltean <vladimir.oltean@....com>
> 
> The ENETC port 0 MAC supports in-band status signaling coming from a PHY
> when operating in RGMII mode, and this feature is enabled by default.
> 
> It has been reported that RGMII is broken in fixed-link, and that is not
> surprising considering the fact that no PHY is attached to the MAC in
> that case, but a switch.
> 
> This brings us to the topic of the patch: the enetc driver should have
> not enabled the optional in-band status signaling for RGMII unconditionally,
> but should have forced the speed and duplex to what was resolved by
> phylink.
> 
> Note that phylink does not accept the RGMII modes as valid for in-band
> signaling, and these operate a bit differently than 1000base-x and SGMII
> (notably there is no clause 37 state machine so no ACK required from the
> MAC, instead the PHY sends extra code words on RXD[3:0] whenever it is
> not transmitting something else, so it should be safe to leave a PHY
> with this option unconditionally enabled even if we ignore it). The spec
> talks about this here:
> https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/138/RGMIIv1_5F00_3.pdf
> 
> Fixes: 71b77a7a27a3 ("enetc: Migrate to PHYLINK and PCS_LYNX")
> Cc: Florian Fainelli <f.fainelli@...il.com>
> Cc: Andrew Lunn <andrew@...n.ch>
> Cc: Russell King <rmk+kernel@...linux.org.uk>

Looks better, thanks.

Acked-by: Russell King <rmk+kernel@...linux.org.uk>

> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> ---
> Changes in v2:
> - Don't write to the MAC if speed and duplex did not change.
> - Don't update the speed with the MAC enabled.
> - Remove the logic for enabling in-band signaling in enetc_mac_config.

-- 
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