Re: [PATCH net-next v9 2/3] net: ethtool: add KSZ87xx low-loss cable PHY tunables

[Marek Vasut]

On 6/5/26 4:35 AM, Jakub Kicinski wrote:
> On Thu,  4 Jun 2026 13:41:19 +0200 Paolo Abeni wrote:
> > > @@ -3114,6 +3114,9 @@ static int ethtool_phy_tunable_valid(const struct ethtool_tunable *tuna)
> > >   	switch (tuna->id) {
> > >   	case ETHTOOL_PHY_DOWNSHIFT:
> > >   	case ETHTOOL_PHY_FAST_LINK_DOWN:
> > > +	case ETHTOOL_PHY_SHORT_CABLE_PRESET:
> > > +	case ETHTOOL_PHY_LPF_BW:
> > > +	case ETHTOOL_PHY_DSP_EQ_INIT_VALUE:
> > >   		if (tuna->len != sizeof(u8) ||
> > >   		    tuna->type_id != ETHTOOL_TUNABLE_U8)
> > >   			return -EINVAL;
> >
> > [Severity: High]
> > Is it intentional to enforce an 8-bit type constraint for bandwidth and DSP
> > equalizer tunables?
> >
> > This heavily couples the global API to the 8-bit register layout of the
> > KSZ87xx hardware without defining generic units like Hz for bandwidth.
>
> AFAIK this is the one comment from AI that survives scrutiny.
> Seems unlikely we'd need more bits, but then again - why not.
> u32 should be our default for integer values, u8 is more for
> booleans.

Why waste memory space if we are already sure the space would not be used.