netdev - Re: [PATCH 1/9] net: ethernet: mtk_eth_soc: add support for MT7981 SoC

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Date:   Fri, 3 Feb 2023 16:18:40 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Daniel Golle <daniel@...rotopia.org>
Cc:     netdev@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Russell King <linux@...linux.org.uk>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Mark Lee <Mark-MC.Lee@...iatek.com>,
        John Crispin <john@...ozen.org>, Felix Fietkau <nbd@....name>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        DENG Qingfang <dqfext@...il.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        Sean Wang <sean.wang@...iatek.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Jianhui Zhao <zhaojh329@...il.com>,
        Bjørn Mork <bjorn@...k.no>
Subject: Re: [PATCH 1/9] net: ethernet: mtk_eth_soc: add support for MT7981
 SoC

On Fri, Feb 03, 2023 at 07:00:21AM +0000, Daniel Golle wrote:
> The MediaTek MT7981 SoC comes two 1G/2.5G SGMII, just like MT7986.
> 
> In addition MT7981 comes with a built-in 1000Base-T PHY which can be
> used with GMAC1.
> 
> As many MT7981 boards make use of swapping SGMII phase and neutral, add
> new device-tree attribute 'mediatek,pn_swap' to support them.
> 
> Signed-off-by: Daniel Golle <daniel@...rotopia.org>
> ---

Phase and neutral? What is this, a power plug?
Since SGMII uses differential signaling, I wonder if this isn't about
the polarity of the TX lane (which pin carries the Positive signal and
which the Negative one).

I think there is room for a more general device tree property name than
"mediatek,pn_swap". The Designware XPCS also supports this, see
DW_VR_MII_DIG_CTRL2_TX_POL_INV and the comments in
nxp_sja1105_sgmii_pma_config().