[powerstation-owners] questions about boot debugging

[Alexander Graf]

Hi Tejun,

On 08.06.2009, at 11:43, Tejun Heo wrote:

> Hello,
>
> I'm messing with early boot code in Linux and the kernel dies after
> prom access goes away but before printk comes online.  early_setup()
> finishes fine but gets stuck after rfid enables RI/DI.  The machine
> simply hangs and I have no way of finding out where the problem
> occurred (my last resort on x86 is combination of infinite loop and
> reset by doublefault but dunno how to do something like that on
> powerpc).

 From my limited understanding you'd have to poke the BMC to do the  
reset. No idea how to do that though. Can't you just dump random  
characters on the serial console + infinite loops?

> The udbg stuff looks like the equivalent of early_printk() on x86 and
> RTAS_PANEL/CONSOLE seems to be the right one but the machine hangs if
> I enable it.  I ordered rj45 to db9 gender hoping that I could get
> more information from the debug port, so my questions are...
>
> 1. The rj45 gender needs to be wired.  There seems to be several
>   different rj45 to db9 mappings.  How should I wire it?
>
> 2. Is the debug port gonna help at all?

The debug port is a simple serial console interface. If you only need  
the machine temporarily I have one you could access with debug port  
attached.

> 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.

Do you need to do this on a powerstation? I improved qemu recently to  
boot pretty far into Linux. The only missing part are external  
interrupts, but as early as you are that shouldn't really matter. Ping  
me if you need help getting that to work.

Alex