[coreboot] Serial Console only starts after reset

Joseph Smith joe at settoplinux.org
Tue Jun 15 17:54:02 CEST 2010

On Tue, 15 Jun 2010 10:28:51 -0400, Joseph Smith <joe at settoplinux.org>
> On Tue, 15 Jun 2010 16:16:46 +0200, Stefan Reinauer
<stepan at coresystems.de>
> wrote:
>> On 6/15/10 4:07 PM, Joseph Smith wrote:
>>> When
>>> I cold boot it, if I hit the reset button before Linux starts, it
>> restarts
>>> with coreboot serial console just fine.
>> Hm...
>> Maybe 0x2e/0x4e are mapped to LPC after the SuperIO is configured (and
>> that mapping survives a reset)... that would be a southbridge init
> Hmm, This is interesting. The first time I booted it, I had copied
> from another board that had:
> And I got coreboot serial console (early_serial) just fine but when it
> to detecting and inializing the superio, I got all kinds of errors from
> coreboot about device not found.
> So I changed it to 0x2e as described in the datasheet and detected with
> superiotool(vendor bios), and that is when this problem started. But now
> coreboot is happy, detects the device and the resource allocator is
> I just do not get early_serial on cold boot.
> This is weird!
>> Or, the hardware has to stabilize after power on before you can
>> configure the SuperIO.
> Maybe?
Hmm from page 142 in the datasheet, I need to figure out of there is a
pull-down resistor connected to the SYSOPT pin to use 0x2e or if there is a
pull-up resistor connected to the SYSOPT pin to use 0x4e. And once powered
up the configuration port base address can be changed through CR26 and

I bet you that there is a pull-up resistor connected to the SYSOPT pin and
0x4e is supposed to be used. And the vendor bios changes this to 0x2e at
some point. That is what is throwing me off!

So I will try:


and change all the devices in devicetree.cb to 4e.

My question is does it need to get changed to 0x2e at some point? Or can I
just leave it at 0x4e? Will it matter to OS?

Thanks for all the brainstorming help Stefan and Ron.

Joseph Smith

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