Re: [PATCH 6/7] netdev: octeon-ethernet: Add Cavium Octeon III support.

From: David Daney <ddaney@caviumnetworks.com>
To: Andrew Lunn <andrew@lunn.ch>
Cc: David Daney <david.daney@cavium.com>,
	linux-mips@linux-mips.org, ralf@linux-mips.org,
	James Hogan <james.hogan@mips.com>,
	netdev@vger.kernel.org, "David S. Miller" <davem@davemloft.net>,
	Rob Herring <robh+dt@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	linux-kernel@vger.kernel.org,
	"Steven J. Hill" <steven.hill@cavium.com>,
	devicetree@vger.kernel.org, Carlos Munoz <cmunoz@cavium.com>
Subject: Re: [PATCH 6/7] netdev: octeon-ethernet: Add Cavium Octeon III support.
Date: Thu, 2 Nov 2017 11:31:45 -0700	[thread overview]
Message-ID: <0168761e-cb18-e489-4689-8c9062aa316b@caviumnetworks.com> (raw)
In-Reply-To: <20171102165605.GJ24320@lunn.ch>

On 11/02/2017 09:56 AM, Andrew Lunn wrote:
>> OK, now I think I understand.  Yes, the MAC can be hardwired to a switch.
>> In fact, there are system designs that do exactly that.
>>
>> We try to handle this case by not having a "phy-handle" property in the
>> device tree.  The link to the remote device (switch IC in this case) is
>> brought up on ndo_open()
> 
> O.K, so you totally ignore the Linux way of doing this and hack
> together your own proprietary solution.

I am going to add handling of the "phy-mode" property, but other than 
that I don't know what the "Linux way" of specifying a hard MAC-to-MAC 
connection with no intervening phy devices is.  Wether the remote MAC is 
a switch, or something else, would seem to be irrelevant.  All we are 
concerned about in this code is putting the thing into a state where 
data flows in both directions through the MAC.

A pointer to an existing device tree binding for an Ethernet device that 
has no (or an optional) phy device would be useful, we can try to do the 
same.

>   
>> There may be opportunities to improve how this works in the future, but the
>> current code is serviceable.
> 
> It might be serviceable, but it will never get into mainline. For
> mainline, you need to use DSA.
> 
> http://elixir.free-electrons.com/linux/v4.9.60/source/Documentation/networking/dsa/dsa.txt

I am truly at a loss here.  That DSA document states:

      Master network devices are regular, unmodified Linux
      network device drivers for the CPU/management Ethernet
      interface.

What modification do you suggest I make?

> 
> Getting back to my original point, having these platform devices can
> cause issues for DSA. Freescale FMAN has a similar architecture, and
> it took a while to restructure it to make DSA work.
> 
> https://www.spinics.net/lists/netdev/msg459394.html
> 
> 	Andrew
> 