RE: [PATCH v2 net-next] net: phy: micrel: Adding SQI support for lan8814 phy

[<Divya.Koppera@microchip.com>]

Hi Andrew,

> -----Original Message-----
> From: Andrew Lunn <andrew@lunn.ch>
> Sent: Monday, September 5, 2022 6:40 PM
> To: Divya Koppera - I30481 <Divya.Koppera@microchip.com>
> Cc: hkallweit1@gmail.com; linux@armlinux.org.uk; davem@davemloft.net;
> edumazet@google.com; kuba@kernel.org; pabeni@redhat.com;
> netdev@vger.kernel.org; linux-kernel@vger.kernel.org; UNGLinuxDriver
> <UNGLinuxDriver@microchip.com>
> Subject: Re: [PATCH v2 net-next] net: phy: micrel: Adding SQI support for
> lan8814 phy
> 
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> On Mon, Sep 05, 2022 at 03:47:30PM +0530, Divya Koppera wrote:
> > 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. It is not supported
> > for 10Mbps speed
> >
> > Signed-off-by: Divya Koppera <Divya.Koppera@microchip.com>
> > ---
> > v1 -> v2
> > - Given SQI support for all pairs of wires in 1000/100 base-T phy's
> >   uAPI may run through all instances in future. At present returning
> >   only first instance as uAPI supports for only 1 pair.
> > - SQI is not supported for 10Mbps speed, handled accordingly.
> 
> I would prefer you solve the problem of returning all pairs.
> 

I will try to improve uAPI. 

The other way I can try is the point you mentioned below to write helper with pair number and having function cal with pair 0.


> I'm not sure how useful the current implementation is, especially at
> 100Mbps, where pair 0 could actually be the transmit pair. Does it give a
> sensible value in that case?
> 

We do have SQI support for 100Mbps to pair 0 only. For other pairs SQI values are invalid values.

> > +static int lan8814_get_sqi(struct phy_device *phydev) {
> > +     int ret, val, pair;
> > +     int sqi_val[4];
> > +
> > +     if (phydev->speed == SPEED_10)
> > +             return -EOPNOTSUPP;
> > +
> > +     for (pair = 0; pair < 4; pair++) {
> > +             val = lanphy_read_page_reg(phydev, 1, LAN8814_DCQ_CTRL);
> > +             if (val < 0)
> > +                     return val;
> > +
> > +             val &= ~LAN8814_DCQ_CTRL_CHANNEL_MASK;
> > +             val |= pair;
> > +             val |= LAN8814_DCQ_CTRL_READ_CAPTURE_;
> > +             ret = lanphy_write_page_reg(phydev, 1, LAN8814_DCQ_CTRL, val);
> > +             if (ret < 0)
> > +                     return ret;
> > +
> > +             ret = lanphy_read_page_reg(phydev, 1, LAN8814_DCQ_SQI);
> > +             if (ret < 0)
> > +                     return ret;
> > +
> > +             sqi_val[pair] = FIELD_GET(LAN8814_DCQ_SQI_VAL_MASK, ret);
> > +     }
> > +
> > +     return *sqi_val;
> 
> How is this going to work in the future? sqi_val is on the stack. You cannot
> return a pointer to it. So this function is going to need modifications.
> 
> If you really want to prepare for a future implementation which could return
> all four, i would probably make this a helper which takes a pair number. And
> then have a function call it once for pair 0.
> 

I Will go for resolving this if I couldn't resolve that 4 pair issue in uAPI.

>      Andrew

Thanks,
Divya