netdev - Re: [PATCH net-next 1/6] ethtool: Extend link modes settings uAPI with lanes

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Date:   Wed, 21 Oct 2020 10:47:33 +0200
From:   Michal Kubecek <mkubecek@...e.cz>
To:     Danielle Ratson <danieller@...dia.com>
Cc:     Jiri Pirko <jiri@...nulli.us>, Andrew Lunn <andrew@...n.ch>,
        Jakub Kicinski <kuba@...nel.org>,
        Ido Schimmel <idosch@...sch.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        Jiri Pirko <jiri@...dia.com>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        mlxsw <mlxsw@...dia.com>, Ido Schimmel <idosch@...dia.com>,
        "johannes@...solutions.net" <johannes@...solutions.net>
Subject: Re: [PATCH net-next 1/6] ethtool: Extend link modes settings uAPI
 with lanes

On Wed, Oct 21, 2020 at 07:20:22AM +0000, Danielle Ratson wrote:
> > -----Original Message-----
> > From: Michal Kubecek <mkubecek@...e.cz>
> > Sent: Wednesday, October 21, 2020 10:08 AM
> > 
> > On Tue, Oct 20, 2020 at 07:39:13AM +0000, Danielle Ratson wrote:
> > > > -----Original Message-----
> > > > From: Michal Kubecek <mkubecek@...e.cz>
> > > > Sent: Monday, October 19, 2020 4:25 PM
> > > >
> > > > As I said, I meant the extension suggested in my mail as independent
> > > > of what this series is about. For lanes count selector, I find
> > > > proposed
> > > >
> > > >   ethtool -s <dev> ... lanes <lanes_num> ...
> > > >
> > > > the most natural.
> > > >
> > > > From purely syntactic/semantic point of view, there are three types
> > > > of
> > > > requests:
> > > >
> > > >   (1) enable specific set of modes, disable the rest
> > > >   (2) enable/disable specific modes, leave the rest as they are
> > > >   (3) enable modes matching a condition (and disable the rest)
> > > >
> > > > What I proposed was to allow the use symbolic names instead of masks
> > > > (which are getting more and more awful with each new mode) also for
> > > > (1), like they can already be used for (2).
> > > >
> > > > The lanes selector is an extension of (3) which I would prefer not
> > > > to mix with
> > > > (1) or (2) within one command line, i.e. either "advertise" or
> > > > "speed / duplex / lanes".
> > > >
> > > > IIUC Jakub's and Andrew's comments were not so much about the syntax
> > > > and semantic (which is quite clear) but rather about the question if
> > > > the requests like "advertise exactly the modes with (100Gb/s speed
> > > > and) two lanes" would really address a real life need and wouldn't
> > > > be more often used as shortcuts for "advertise 100000baseKR2/Full".
> > > > (On the other hand, I suspect existing speed and duplex selectors
> > > > are often used the same way.)
> > > >
> > > > Michal
> > >
> > > So, do you want to change the current approach somehow or we are good
> > > to go with this one, keeping in mind the future extension you have
> > > suggested?
> > 
> > As far as I'm concerned, it makes sense as it is. The only thing I'm not happy
> > about is ETHTOOL_A_LINKMODES_LANES being a "write only" attribute
> > (unlike _SPEED and _DUPLEX) but being able to query this information would
> > require extensive changes far beyond the scope of this series.
> 
> If I understood you correctly, patch #5 does that query, isn't it?
> "mlxsw: ethtool: Expose the number of lanes in use"

Ah, right, it does. But as you extend struct ethtool_link_ksettings and
drivers will need to be updated to provide this information, wouldn't it
be more useful to let the driver provide link mode in use instead (and
derive number of lanes from it)?

Michal