No console output when booting linux from uboot

Qin, Laigui (GE EntSol, Security) laigui.qin at
Thu Jun 5 11:55:20 EST 2008

Thanks. Now I am confusing with the way uboot passing parameters to
linux kernel:

in Uboot 1.2.0: Kernel is entered through the following calling
        theKernel (linux_argc, linux_argv, linux_env, 0);
while in Uboot 1.3.0:
        (*kernel) (kbd, initrd_start, initrd_end, cmd_start, cmd_end);

The linux kernel I used is designed with Uboot 1.2.0, while I used
1.3.2. Will this be a problem for passing the parameters?

Mike Qin

-----Original Message-----
From: at
[ at] On
Behalf Of Detlev Zundel
Sent: Thursday, June 05, 2008 12:31 AM
To: linuxppc-embedded at
Subject: Re: No console output when booting linux from uboot

Hi Mike,

> I am trying to boot linux kernel (2.6.23) from uboot (1.3.2) for my 
> custom board. The uboot works well, the kernel booting hit the 
> start_kernel(). But there is nothing output from console.

Do you provide a correct "console=..." parameter?

> With debugger, I saw that the printk() functions were called many 
> times without any console output. Tracing into the source code, I 
> found that the printk() called "con->write" operation...
> Can anyone guide me to solve this?

I have a hint concerning an incorrect conjecture from your side.
Usually when start_kernel starts, the kernel knows nothing about
consoles to output printk messages to, so in the early phases the
printk's (like printk(KERN_NOTICE)) only end up in the internal ring
buffer.  Its only later when the console is associated with a real
device that everything gets sent there.

So you shouldn't really wonder why early printk's do not output
anything, this is a red herring.  Debug the code responsible for the hw
acting as your console according to the kernel command line.


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