linux-kernel - Re: [PATCH net-next] net: phy: micrel: Adding SQI support for lan8814 phy

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Date:   Fri, 26 Aug 2022 21:51:29 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Oleksij Rempel <o.rempel@...gutronix.de>
Cc:     Michael Walle <michael@...le.cc>, Divya.Koppera@...rochip.com,
        UNGLinuxDriver@...rochip.com, davem@...emloft.net,
        edumazet@...gle.com, hkallweit1@...il.com, kuba@...nel.org,
        linux-kernel@...r.kernel.org, linux@...linux.org.uk,
        netdev@...r.kernel.org, pabeni@...hat.com
Subject: Re: [PATCH net-next] net: phy: micrel: Adding SQI support for
 lan8814 phy

> > > In lan8814 phy only channel 0 is used for 100base-tx. So returning SQI
> > > value for channel 0.
> > 
> > What if the other pairs are bad? Maybe Oleksij has an opinion here.
> > 
> > Also 100baseTX (and 10baseT) has two pairs, one for transmitting and one
> > for receiving. I guess you meassure the SQI on the receiving side. So is
> > channel 0 correct here?
> > 
> > Again this is the first time I hear about SQI but it puzzles me that
> > it only evaluate one pair in this case. So as a user who reads this
> > SQI might be misleaded.
> 
> Wow! I was so possessed with one-pair networks, that forgot to image
> that there is 1000Base-T with more then one pairs :D
> 
> Yes, your are right. We wont to have readings from all RX channels and
> be able to export them to the user space. In fact, if i see it
> correctly, the LAN8814_DCQ_CTRL_CHANNEL_MASK value should be synced with
> the MDI-X state. Otherwise we will be reading TX channels.

I don't know if i should trust the datasheet i found, but it suggests
the register in MMD device 1 space has a field to indicate which cable
pair should be measured. So for 1000Base-T all pairs are both Rx and
Tx, so i would expect 4 values are returned. That then might need an
uAPI extension, if you were focused on T1 :-)

    Andrew