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

Andrew Lunn
2022-08-26T19:51:47Z

> > > 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