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

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Date:	Sun, 1 Jul 2007 17:00:06 +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 Sun, Jul 01, 2007 at 12:23:16PM +0200, Michael Buesch wrote:

> > More or less.  You can't add the resistances like that, since the
> > bus isolation chip buffers the IDSEL signal, but it is correct that
> > if the host's IDSEL resistor is larger than a certain value, the
> > combination of the resistive coupling of IDSEL plus the extra buffer
> > in the isolator might be causing the IDSEL input on the 'guest' PCI
> > board to assert too late (or not assert at all), causing config
> > accesses to fail.
> > 
> > (This also depends on the specific 'guest' PCI board used, as you
> > noted, due to differing IDSEL trace lengths/capacitances and input
> > pin capacitances on different PCI boards.  Also, it might work at
> > 33 MHz but not work at 66 MHz, etc.)
> 
> It doesn't work on any of my boards :(

What extender board is this?  Do you have docs/schematics?
And what motherboard brand/type?


> > If you feel adventurous, you could try to hack around this by
> > figuring out which AD[31:16] line this PCI slot's IDSEL line is
> > resistively coupled to (depends on the slot), and then adding
> > another parallel resistor on the board itself to make the bus
> > isolator's input buffer charge faster.  Note that this does
> > increase the load on that specific AD[] line, which might cause
> > other funny effects.
> 
> Well, but how to find out to which address line it's connected to?
> Pretty hard to follow the PCB traces, especially since it's
> multilayered.

Actually, the IDSEL resistor would be on the computer's
motherboard, not on the PCI board.  And to which address line
the IDSEL line is connected depends on which PCI slot on the
motherboard you're looking at.

A multimeter should do the trick, but I would advise against this
if you're not totally comfortable with hacking hardware.
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