Re: Broken ethernet on SolidRun cubox-i - Russell King

From: Russell King - ARM Linux admin <linux@armlinux.org.uk>
To: Michael Walle <michael@walle.cc>
Cc: Matus Ujhelyi <ujhelyi.m@gmail.com>,
	acmattheis@gmx.net,
	Christoph Mattheis <christoph.mattheis@arcor.de>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: Broken ethernet on SolidRun cubox-i
Date: Sun, 27 Dec 2020 16:11:15 +0000	[thread overview]
Message-ID: <20201227161114.GF1551@shell.armlinux.org.uk> (raw)
In-Reply-To: <a04a56fccd29329ba4a8624c015a5c2e@walle.cc>

On Sun, Dec 27, 2020 at 04:59:39PM +0100, Michael Walle wrote:
> Am 2020-12-27 16:33, schrieb Michael Walle:
> > Am 2020-12-26 13:34, schrieb Russell King - ARM Linux admin:
> > > I'd forgotten that there were boards out there with this problem...
> > > the PHY address configuration is done via the LED_ACT pin, and
> > > SolidRun
> > > omitted a pull resistor on it, so it "floats" with the leakage current
> > > of the LED/pin - resulting in it sometimes appearing at address 0 and
> > > sometimes at address 4.
> > 
> > Mh, I've guessed that too, but there must be more to it. The datasheet
> > says it has an internal weak pull-up. Or Atheros messed up and it
> > doesn't
> > reliably work if there is actually an LED attached to it. But then, why
> > would any other stronger pull-up/down work..
> 
> Mhh, nevermind, from the commit log [1].
> 
>   "The LED_ACT pin on the carrier-one boards had a pull down that
>   forces the phy address to 0x0; where on CuBox-i and the production
>   HummingBoard that pin is connected directly to LED that depending
>   on the pull down strength of the LED it might be sampled as '0' or '1'
> thus
>   the phy address might appear as either address 0x0 or 0x4."
> 
> So it actually depends on the forward voltage of the LED and the
> hi/low thresholds of the AT8035.. nice! Oh and btw. this pin also
> switches between high and low-active LED output. So the missing
> pull-down might not only switch the PHY address to 4 but also invert
> the LED state.

Indeed. And whether it appears at address 0 or 4 will depend on many
factors, including temperature - LEDs have a decrease of 2mV/°C.

I wonder if we can just delete the phy-handle property, and list a
PHY at both address 0 and 4 with the appropriate configuration...

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!

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