netdev - Re: [PATCH v2] net: mtk_sgmii: implement mtk_pcs

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Message-ID: <87h6wq35dn.fsf@miraculix.mork.no>
Date:   Mon, 16 Jan 2023 15:45:24 +0100
From:   Bjørn Mork <bjorn@...k.no>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     Frank Wunderlich <frank-w@...lic-files.de>,
        Frank Wunderlich <linux@...web.de>,
        linux-mediatek@...ts.infradead.org,
        Alexander Couzens <lynxis@...0.eu>,
        Felix Fietkau <nbd@....name>, John Crispin <john@...ozen.org>,
        Sean Wang <sean.wang@...iatek.com>,
        Mark Lee <Mark-MC.Lee@...iatek.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>,
        netdev@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] net: mtk_sgmii: implement mtk_pcs_ops

"Russell King (Oracle)" <linux@...linux.org.uk> writes:
> On Mon, Jan 16, 2023 at 02:08:30PM +0100, Bjørn Mork wrote:
>> Frank Wunderlich <frank-w@...lic-files.de> writes:
>> 
>> > apart from this little problem it works much better than it actually is so imho more
>> > people should test it on different platforms.
>> 
>> Hello!  I've been banging my head against an MT7986 board with two
>> Maxlinear GPY211C phys for a while. One of those phys is connected to
>> port 5 of the MT7531 switch.  This is working perfectly.
>> 
>> The other GPY211C is connected to the second MT7986 mac.  This one is
>> giving me a headache...
>> 
>> I can only get the port to work at 2500Mb/s.  Changing the speed to
>> anything lower looks fine in ethtool etc, but traffic is blocked.
>
> My guess would be that the GPY PHY is using in-band SGMII negotiation
> (it sets VSPEC1_SGMII_ANEN_ANRS when entering SGMII mode and clears
> it in 2500base-X), but as the link is not using in-band mode on the
> PCS side, the PHY never sees its in-band negotiation complete, so the
> link between PCS and PHY never comes up.
>
> Both sides need to agree on that detail.

Any hints on how I would go about doing that?  I am a little lost here,
changing arbitrary bits I don't understand the meaning of.


Bjørn