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

[Divya.Koppera]

Hi Michael,

> -----Original Message-----
> From: Michael Walle <michael@xxxxxxxx>
> Sent: Friday, August 26, 2022 2:56 PM
> To: Divya Koppera - I30481 <Divya.Koppera@xxxxxxxxxxxxx>; Oleksij Rempel
> <o.rempel@xxxxxxxxxxxxxx>
> Cc: UNGLinuxDriver <UNGLinuxDriver@xxxxxxxxxxxxx>; andrew@xxxxxxx;
> davem@xxxxxxxxxxxxx; edumazet@xxxxxxxxxx; hkallweit1@xxxxxxxxx;
> kuba@xxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux@xxxxxxxxxxxxxxx;
> netdev@xxxxxxxxxxxxxxx; pabeni@xxxxxxxxxx
> Subject: Re: [PATCH net-next] net: phy: micrel: Adding SQI support for
> lan8814 phy
> 
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> 
> [+ Oleksij Rempel]
> 
> Hi,
> 
> Am 2022-08-26 11:11, schrieb Divya.Koppera@xxxxxxxxxxxxx:
> >> > 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@xxxxxxxxxxxxx>
> 
> ..
> 
> >> > +#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.
> 

I just looked into it, it doesn't have SQI registers. I requested internal team to add SQI register set in published document.

> >
> >> 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@xxxxxxxxxxxxxx/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?
> 

Yes Channel 0 is correct.

> 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.
> 

Yeah, It needs uAPI extension.

> -michael