Re: [PATCH net v2 1/1] ethtool: netlink: do not return SQI value if link is down

[Oleksij Rempel <o.rempel@pengutronix.de>]

Hi Woojung,

On Mon, Jul 08, 2024 at 04:31:53PM +0000, Woojung.Huh@microchip.com wrote:
> Hi Oleksij,
> 
> > diff --git a/net/ethtool/linkstate.c b/net/ethtool/linkstate.c
> > index b2de2108b356a..4efd327ba5d92 100644
> > --- a/net/ethtool/linkstate.c
> > +++ b/net/ethtool/linkstate.c
> > @@ -37,6 +37,8 @@ static int linkstate_get_sqi(struct net_device *dev)
> >         mutex_lock(&phydev->lock);
> >         if (!phydev->drv || !phydev->drv->get_sqi)
> >                 ret = -EOPNOTSUPP;
> > +       else if (!phydev->link)
> > +               ret = -ENETDOWN;
> >         else
> >                 ret = phydev->drv->get_sqi(phydev);
> >         mutex_unlock(&phydev->lock);
> > @@ -55,6 +57,8 @@ static int linkstate_get_sqi_max(struct net_device *dev)
> >         mutex_lock(&phydev->lock);
> >         if (!phydev->drv || !phydev->drv->get_sqi_max)
> >                 ret = -EOPNOTSUPP;
> > +       else if (!phydev->link)
> > +               ret = -ENETDOWN;
> >         else
> >                 ret = phydev->drv->get_sqi_max(phydev);
> >         mutex_unlock(&phydev->lock);
> > @@ -62,6 +66,16 @@ static int linkstate_get_sqi_max(struct net_device *dev)
> >         return ret;
> >  };
> > 
> > +static bool linkstate_sqi_critical_error(int sqi)
> > +{
> > +       return sqi < 0 && sqi != -EOPNOTSUPP && sqi != -ENETDOWN;
> > +}
> > +
> > +static bool linkstate_sqi_valid(struct linkstate_reply_data *data)
> > +{
> > +       return data->sqi >= 0 && data->sqi_max >= 0;
> 
> If PHY driver has get_sqi, but not get_sqi_max, then data->sqi could have
> a valid value, but data->sqi_max will have -EOPNOTSUPP.
> In this case, linkstate_sqi_valid() will return FALSE and not getting 
> SQI value at all.

SQI without max will not able to describe quality of the link, it is
just value saying nothing to the user.

> If both APIs are required, then we could add another condition of
> data->sqi <= data->sqi_max in linkstate_sqi_valid()

Ack. I was thinking about it, but was not sure if it is a good idea. This
will silently filer our a bag. Passing a baggy value to the users space
is not good too. I'll fix.

> And, beside this, calling linkstate_get_sqi and linkstate_get_sqi_max
> could be moved under "if (dev->flags & IFF_UP)" with setting default 
> value to data->sqi & data->sqi_max.

IFF_UP is administrative up state, it is not the link/L1 up. sqi_max and
sqi should be initialized anyway, otherwise we will show 0/0 if
interface is in admin down.

Regards,
Oleksij
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