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

Oleksij Rempel
2022-08-26T10:43:56Z

On Fri, Aug 26, 2022 at 11:54:29AM +0200, Oleksij Rempel wrote:
> Hi,
>
> On Fri, Aug 26, 2022 at 11:26:12AM +0200, Michael Walle wrote:
> > [+ Oleksij Rempel]
> >
> > Hi,
> >
> > Am 2022-08-26 11:11, schrieb Divya.Koppera@microchip.com:
> > > > > Supports SQI(Signal Quality Index) for lan8814 phy, where it has SQI
> > > > > index of 0-7 values and this indicator can be used for cable integrity
> > > > > diagnostic and investigating other noise sources.
> > > > >
> > > > > Signed-off-by: Divya Koppera <Divya.Koppera@microchip.com>
> >
> > ..
> >
> > > > > +#define LAN8814_DCQ_CTRL_CHANNEL_MASK GENMASK(1,
> > > > 0)
> > > > > +#define LAN8814_DCQ_SQI 0xe4
> > > > > +#define LAN8814_DCQ_SQI_MAX 7
> > > > > +#define LAN8814_DCQ_SQI_VAL_MASK GENMASK(3, 1)
> > > > > +
> > > > > static int lanphy_read_page_reg(struct phy_device *phydev, int page,
> > > > > u32 addr) {
> > > > > int data;
> > > > > @@ -2927,6 +2934,32 @@ static int lan8814_probe(struct phy_device
> > > > *phydev)
> > > > > return 0;
> > > > > }
> > > > >
> > > > > +static int lan8814_get_sqi(struct phy_device *phydev) {
> > > > > + int rc, val;
> > > > > +
> > > > > + val = lanphy_read_page_reg(phydev, 1, LAN8814_DCQ_CTRL);
> > > > > + if (val < 0)
> > > > > + return val;
> > > > > +
> > > > > + val &= ~LAN8814_DCQ_CTRL_CHANNEL_MASK;
> > > >
> > > > I do have a datasheet for this PHY, but it doesn't mention 0xe6 on
> > > > EP1.
> > >
> > > This register values are present in GPHY hard macro as below
> > >
> > > 4.2.225 DCQ Control Register
> > > Index (In Decimal): EP 1.230 Size: 16 bits
> > >
> > > Can you give me the name of the datasheet which you are following, so
> > > that I'll check and let you know the reason.
> >
> > I have the AN4286/DS00004286A ("LAN8804/LAN8814 GPHY Register
> > Definitions"). Maybe there is a newer version of it.
> >
> > >
> > > > So I can only guess that this "channel mask" is for the 4 rx/tx
> > > > pairs on GbE?
> > >
> > > Yes channel mask is for wire pair.
> > >
> > > > And you only seem to evaluate one of them. Is that the correct thing
> > > > to do
> > > > here?
> > > >
> > >
> > > I found in below link is that, get_SQI returns sqi value for 100 base-t1
> > > phy's
> > > https://lore.kernel.org/netdev/20200519075200.24631-2-o.rempel@pengutronix.de/T/
> >
> > That one is for the 100base-t1 which has only one pair.
> >
> > > 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.

Just an idea not really related to this patch. It will be coll to be
able to generate diagnostic graphs like this:

Interface | pairs | data | power | SQI | cable | selft
| direction | | | test | test
eth0 ok
0 | RX | NC | 7/7 | ok |
1 | TX | NC | NA | ok |
2 | NC | + 10W | NA | ok |
3 | NC | - | NA | ok |

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