netdev - Re: [PATCH] net: phy: Add config option to specify external switch port to be used if switch is used as PHY

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Message-ID: <4E68922D.8020805@televic.com>
Date:	Thu, 8 Sep 2011 12:00:13 +0200
From:	Lambrecht Jürgen <J.Lambrecht@...EVIC.com>
To:	Florian Fainelli <florian@...nwrt.org>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-embedded@...r.kernel.org" <linux-embedded@...r.kernel.org>
Subject: Re: [PATCH] net: phy: Add config option to specify external switch
 port to be used if switch is used as PHY

On 09/08/2011 10:39 AM, Florian Fainelli wrote:
>
> Hello Jurgen,
>
> On Thursday 08 September 2011 08:54:07 Lambrecht Jürgen wrote:
> > Hello,
> >
> > In our embedded designs, this is a useful patch. Maybe it can be useful
> > for somebody else too.
> > Or maybe there are already better solutions?
> > I know I could also write a driver for our switch, but that is too much
> > effort just to select the active port.
>
> This is not going to work well with all switches out there. You could 
> use the
>
Do not all switches follow the basic MII register map with room for 31 
phy's?
>
> fixed-PHY driver to make your ethernet driver see the link as always 
> up between
> the MAC and switch CPU port.
>
Indeed, I tried to, but it didn't work. (would be my preferred solution)
I juist enabled FIXED_PHY in menuconfig (and kept MII, NET_ETHERNET and 
FEC (for my iMX cpu); also PHYLIB is on that makes mdio_bus.c compile). 
I checked the architecture file for mpc866ads and didn't find any init 
for it, but maybe I need to initialize fixed-PHY somewhere?

However, it could be interesting sometimes from application side to know 
if the real external link is up, then fixed-PHY is not ok.
>
>
> A better solution would be to have proper switch drivers and 
> user-space, which
> reminds me that we (OpenWrt) should at some point propose our switch 
> drivers
> [1] for review.
>
> [1]:
> https://dev.openwrt.org/browser/trunk/target/linux/generic/files/drivers/net/phy/
>
Just had a fast look to the Marvell switch driver. Nice to know it is there.
>
>
> >
> > Kind regards,
> > Jürgen
> >
> >    In embedded design, instead of a PHY, sometimes a switch is used that
> >            behaves as a PHY through its MII port. For example to use a
> > daisy chain network configuration instead of an expensive star 
> config. In
> > that case, many phy ports are available, but only 1 should be used
> >            to check link status, and not the first one available as is
> > the case
> >            without this configuration (that is, set to its default value
> > 0). So this options specifies the switch port number to be used to check
> >            link status, because if the link is down, no data is sent 
> by the
> >            TCP/IP stack.
> >
> > Signed-off-by: Jürgen Lambrecht <J.Lambrecht@...evic.com>
> > ---
>
[snip]
>
> --
> Florian
>


-- 
Jürgen Lambrecht
R&D Associate
Tel: +32 (0)51 303045    Fax: +32 (0)51 310670
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