netdev - Re: [PATCH net-next v2 4/7] devlink: allow subports on devlink PCI ports

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Date:   Mon, 18 Mar 2019 14:29:49 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Parav Pandit <parav@...lanox.com>
Cc:     Jiri Pirko <jiri@...nulli.us>,
        "Samudrala, Sridhar" <sridhar.samudrala@...el.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "oss-drivers@...ronome.com" <oss-drivers@...ronome.com>
Subject: Re: [PATCH net-next v2 4/7] devlink: allow subports on devlink PCI
 ports

On Mon, 18 Mar 2019 20:35:02 +0000, Parav Pandit wrote:
> > > > > physical and pf has some overlapping definitions.  
> > > >
> > > > What "overlapping definitions" do physical and PF have?  
> > > PF has physically user facing port.  
> > 
> > PF doesn't "have a user facing port" in switchdev mode.  
>  
> Physical port described in include/uapi/linux/devlink.h as
> DEVLINK_PORT_FLAVOUR_PHYSICAL is not related to switchdev or legacy
> mode. 

I said "PF doesn't ...", you're now talking about physical?

> As the comment block describe it is 'any kind of port physical
> facing user'. 

Are you saying PCI function is physical?  Just because PF stands for
Physical Function?  

Physical port in devlink means a port in the front panel where
networking cable goes.

> Current mlx5 driver doesn't expose ports as physical regardless of
> switchdev/legacy mode.

Today mlx5 doesn't expose devlink ports at all.

> > It's a limitation of Mellanox HW that you have some strong
> > association there. 
> Not sure why you keep saying that. Any code reference that I should
> look at? Or maybe you can explain what is that limitation, because I
> am not aware of any.

NIC designs originating from traditional NICs were build as pipelines
from PCI to wire or from wire to PCI.  Reportedly it makes it hard to
completely divorce the PCI PF from the wire port (physical port).

Which is why you may think that "PF has physically user facing port".

> > > And physical port in include/uapi/linux/devlink.h also describe
> > > that.  
> > 
> > By "that" you must mean that the physical is a user facing port.  
> 
> Can you please describe the difference between 'PF port' and
> 'physical port of include/uapi/linux/devlink.h'? I must have missed
> this crisp definition in discussion between you and Jiri. I am in
> meantime checking the thread.

Perhaps start with the cover letter which includes an ASCII drawing?

Using Mellanox nomenclature - PF port is a "representor" for the PF
which may be on another Host (SmartNIC or multihost).  It's pretty 
much the same thing as a VF port/"representor".

Physical port is the hole on the panel of the adapter where cable goes.