netdev - Re: [PATCH net-next v1 4/9] net: ethtool: Add attributes for cable test reports

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Message-ID: <743b2495-eab1-01af-1c1c-269f992b802a@gmail.com>
Date:   Wed, 29 Apr 2020 11:58:54 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Andrew Lunn <andrew@...n.ch>, Michael Walle <michael@...le.cc>
Cc:     cphealy@...il.com, davem@...emloft.net, hkallweit1@...il.com,
        mkubecek@...e.cz, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v1 4/9] net: ethtool: Add attributes for cable
 test reports

On 4/29/20 11:57 AM, Andrew Lunn wrote:
> On Wed, Apr 29, 2020 at 06:16:05PM +0200, Michael Walle wrote:
>> Hi,
>>
>>>>>> +enum {
>>>>>> +	ETHTOOL_A_CABLE_PAIR_0,
>>>>>> +	ETHTOOL_A_CABLE_PAIR_1,
>>>>>> +	ETHTOOL_A_CABLE_PAIR_2,
>>>>>> +	ETHTOOL_A_CABLE_PAIR_3,
>>>>>> +};
>>>>>
>>>>> Do we really need this enum, couldn't we simply use a number (possibly
>>>>> with a sanity check of maximum value)?
>>>>
>>>> They are not strictly required. But it helps with consistence. Are the
>>>> pairs numbered 0, 1, 2, 3, or 1, 2, 3, 4?
>>>
>>> OK, I'm not strictly opposed to it, it just felt a bit weird.
>>
>> Speaking of the pairs. What is PAIR_0 and what is PAIR_3? Maybe
>> it is specified somewhere in a standard, but IMHO an example for
>> a normal TP cable would help to prevent wild growth amongst the
>> PHY drivers and would help to provide consistent reporting towards
>> the user space.
> 
> Hi Michael
> 
> Good question
> 
> Section 25.4.3 gives the pin out for 100BaseT. There is no pair
> numbering, just transmit+, transmit- and receive+, receive- signals.
> 
> 1000BaseT calls the signals BI_DA+, BI_DA-, BI_DB+, BI_DB-, BI_DC+,
> BI_DC-, BI_DDA+, BI_DD-. Comparing the pinout 100BaseT would use
> BI_DA+, BI_DA-, BI_DB+, BI_DB. But 1000BaseT does not really have
> transmit and receive pairs due to Auto MDI-X.
> 
> BroadReach calls the one pair it has BI_DA+/BI_DA-.
> 
> Maybe it would be better to have:
> 
> enum {
> 	ETHTOOL_A_CABLE_PAIR_A,
> 	ETHTOOL_A_CABLE_PAIR_B,
> 	ETHTOOL_A_CABLE_PAIR_C,
> 	ETHTOOL_A_CABLE_PAIR_D,
> };

Yes, that would be clearer IMHO. Broadcom PHYs tend to refer to pairs A,
B, C and D in their datasheets.
-- 
Florian