linux-kernel - Re: [PATCH] b44: power down PHY when interface down

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Message-ID: <20070630220301.GD2553@xi.wantstofly.org>
Date:	Sun, 1 Jul 2007 00:03:01 +0200
From:	Lennert Buytenhek <buytenh@...tstofly.org>
To:	Michael Buesch <mb@...sch.de>
Cc:	Török Edvin <edwintorok@...il.com>,
	zambrano@...adcom.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, power@...host.org
Subject: Re: [PATCH] b44: power down PHY when interface down

On Sat, Jun 30, 2007 at 11:53:25PM +0200, Michael Buesch wrote:

> > When the interface is down (or driver removed), the BroadCom 44xx card remains
> > powered on, and both its MAC and PHY is using up power.
> > This patch makes the driver issue a MAC_CTRL_PHY_PDOWN when the interface
> > is halted, and does a partial chip reset turns off the activity LEDs too.
> > 
> > Applies to 2.6.22-rc6, or current git head.
> > 
> > Tested on a Broadcom BCM4401-B0 card, it saves ~0.5W (measured using powertop).
> 
> Hm, I was going to measure the real power advantage with a
> PCI-extender card. But my B44B0 card doesn't seem to work in
> that extender card. It works perfectly fine sticked directly into
> the motherboard, though, and other cards like a BCM4318 work in
> the extender, too.
> Not sure what this is.
> The extender has an application note about nonworking cards in the
> extender and a too big resistor on the board IDSEL pin being the
> cause of this.

Does the card show up in lspci at all?  IDSEL drive strength
issues should only affect config space accesses.

Does the extender board have a PCI-PCI bridge on it?  (If not,
there's not really any reason to resistively couple the IDSEL
line to the host, since the host should take care of that.)

> Maybe I can try with another machine tomorrow.

That would only make a difference if there is no PCI-PCI bridge on
the extender board.

If the extender resistively couples the host's IDSEL line, you might
see different results on a different host bridge, since different
host bridges can use different numbers of IDSEL stepping cycles.
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