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

[Marek Vasut <marex@nabladev.com>]

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.