Re: [PATCH net-next RFC v2 2/6] net: ethtool: Introduce ETHTOOL_LINK_MEDIUM_* values

[Maxime Chevallier <maxime.chevallier@bootlin.com>]

Hi again Köry,

> Hi Köry,
> 
> On Thu, 23 Jan 2025 10:35:34 +0100
> Kory Maincent <kory.maincent@bootlin.com> wrote:
> 
> > On Wed, 22 Jan 2025 18:42:47 +0100
> > Maxime Chevallier <maxime.chevallier@bootlin.com> wrote:
> >   
> > > In an effort to have a better representation of Ethernet ports,
> > > introduce enumeration values representing the various ethernet Mediums.
> > > 
> > > This is part of the 802.3 naming convention, for example :
> > > 
> > > 1000 Base T 4
> > >  |    |   | |
> > >  |    |   | \_ lanes (4)
> > >  |    |   \___ Medium (T == Twisted Copper Pairs)
> > >  |    \_______ Baseband transmission
> > >  \____________ Speed
> > > 
> > >  Other example :
> > > 
> > > 10000 Base K X 4
> > >            | | \_ lanes (4)
> > >            | \___ encoding (BaseX is 8b/10b while BaseR is 66b/64b)
> > >            \_____ Medium (K is backplane ethernet)
> > > 
> > > In the case of representing a physical port, only the medium and number
> > > of lanes should be relevant. One exception would be 1000BaseX, which is
> > > currently also used as a medium in what appears to be any of
> > > 1000BaseSX, 1000BaseFX, 1000BaseCX and 1000BaseLX.    
> > 
> > 
> >   
> > > -	__DEFINE_LINK_MODE_PARAMS(100, T, Half),
> > > -	__DEFINE_LINK_MODE_PARAMS(100, T, Full),
> > > -	__DEFINE_LINK_MODE_PARAMS(1000, T, Half),
> > > -	__DEFINE_LINK_MODE_PARAMS(1000, T, Full),
> > > +	__DEFINE_LINK_MODE_PARAMS_LANES(10, T, 2, 4, Half, T),
> > > +	__DEFINE_LINK_MODE_PARAMS_LANES(10, T, 2, 4, Full, T),
> > > +	__DEFINE_LINK_MODE_PARAMS_LANES(100, T, 2, 4, Half, T),
> > > +	__DEFINE_LINK_MODE_PARAMS_LANES(100, T, 2, 4, Full, T),    
> > 
> >   
> > > -	__DEFINE_LINK_MODE_PARAMS(1000, KX, Full),
> > > -	__DEFINE_LINK_MODE_PARAMS(10000, KX4, Full),
> > > -	__DEFINE_LINK_MODE_PARAMS(10000, KR, Full),
> > > +	__DEFINE_LINK_MODE_PARAMS(1000, KX, Full, K),
> > > +	__DEFINE_LINK_MODE_PARAMS(10000, KX4, Full, K),
> > > +	__DEFINE_LINK_MODE_PARAMS(10000, KR, Full, K),    
> > 
> > The medium information is used twice.
> > Maybe we could redefine the __DEFINE_LINK_MODE_PARAMS like this to avoid
> > redundant information:
> > #define __DEFINE_LINK_MODE_PARAMS(_speed, _medium, _encoding, _lanes, _duplex)
> > 
> > And something like this when the lanes are not a fix number:
> > #define __DEFINE_LINK_MODE_PARAMS_LANES_RANGE(_speed, _medium, _encoding,
> > _min_lanes, _max_lanes, _duplex)
> > 
> > Then we can remove all the __LINK_MODE_LANES_XX defines which may be
> > wrong as you have spotted in patch 1.  
> 
> I will give this a try, see hw this looks, so that we can separate the
> encoding info from the medium info.

So I did give it a go, but it turns out to be much more complex than
expected... The _type information from definitions like :

__DEFINE_LINK_MODE_PARAMS(10000, KX4, Full, K),

(here _type is KX4) can't really be split into the individual
attributes <Medium, Encoding, Lanes> without having some complex macro
logic. This type is used to convert to actual linkmodes that already
exist in the kernel :

#define ETHTOOL_LINK_MODE(speed, type, duplex) \
	ETHTOOL_LINK_MODE_ ## speed ## base ## type ## _ ## duplex ## _BIT

Say we want to generate the _type from <Medium, Encoding, Lanes> with a
macro, we have to cover all the weird cases :

1000BaseT => No encoding, no lanes
10000BaseKX4 => K medium, X encoding, 4 lanes
10000BeseKX => K medium, X encding, no lanes (which means 1 lane)
1000BaseX => Just encoding
100000BaseLR4_ER4 => One link mode that applies for 2 mediums ?

While doable, this will probably end-up more complex and hard to
maintain than re-specifying the medium :(

Maxime