[powerstation-owners] questions about boot debugging

[Tejun Heo]

Hello, James.

James Bottomley wrote:
>> 1. The rj45 gender needs to be wired.  There seems to be several
>>    different rj45 to db9 mappings.  How should I wire it?
> 
> Let me see if I can dig this up:  I had to build a special RJ-45 plug to
> get this to work (of course, I did it ~8 months ago and now don't have
> the details to hand).

That would be great.  Thanks.

>> 2. Is the debug port gonna help at all?
> 
> Sort of ... once you get it up, you see all the BMC and early boot
> output.  It *seems* to be writing console output to it before early
> printk is enabled, but I can't be sure of this.

Hmmm....

> It also responds to the power on/power off BMC keystrokes (if you have
> the updated BMC installed)

Yeap, I did yesterday.

>> 3. Any ideas on how to get early debug output?  At this point, I'll be
>>    _VERY_ happy if I can just get the a double word value written in
>>    some nv storage and then retrieve it after hard reset.
> 
> Not tried, but looking at the output, yaboot can certainly write to it
> (you have to set the open firmware output device for all of this to
> happen) so I'm guessing the kernel can too.

yaboot is calling into the firmware and prom_printf() in kernel is
doing about the same thing.  The problem is that once page translation
is enabled firmware access doesn't really work.  I tried to turn off
page translation and then call into prom to print out debug messages
but it was very unreliable.  It somehow failed depending on the
callsites even when the callsites were only tens of instructions
apart.  :-(

Thanks.

-- 
tejun