netdev - Re: Linux support for 802.3af?

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Message-ID: <1268455203.7439.78.camel@localhost>
Date:	Sat, 13 Mar 2010 04:40:03 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	"Philip A. Prindeville" <philipp_subx@...fish-solutions.com>
Cc:	netdev@...r.kernel.org
Subject: Re: Linux support for 802.3af?

On Fri, 2010-03-12 at 18:11 -0700, Philip A. Prindeville wrote:
> On 03/12/2010 05:43 PM, Ben Hutchings wrote:
> > On Fri, 2010-03-12 at 17:01 -0700, Philip A. Prindeville wrote:
> >> I was looking at this Marvell-based 4-port PCI card with PoE and
> >> thinking it would be handy for powering cameras and ip-phones, but don't
> >> remember seeing any kernel support for 802.3af...
> >>
> >> http://www.korenix.com/jetcard-PoE_Universal_PCI_Card-2215-overview.htm
> >>
> >> There's no support for 802.3af, right?
> > 
> > The standard MDIO ioctls can be used to access registers 11 and 12 on
> > PHYs with integrated PSE functionality.  There is no way of indicating
> > whether a PHY has such functionality, but a flag for this could be added
> > to the mdio_support field of struct ethtool_cmd.
> > 
> > Ben.
> 
> Well, there's more to it than that, right?
> 
> There's a software state machine that's required to go through the
> handshake, there's prioritization and power budgeting, etc.  Yes?
> 
> What am I missing?

We seem to have contrary expectations of how a PSE would be implemented.
You assume that the CPU would be involved at quite a low level.  I
assume that a PSE in a Linux system would be implemented on a peripheral
device and that it would be managed from the host via MDIO (though this
is specified as an optional feature).

Looking at the specs, that particular card is using a Marvell switch
chip which doesn't have any PoE support, so management via MDIO seems
unlikely.  If you're curious I suppose you should try to get the driver
from this vendor.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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