No console output when booting linux from uboot

Detlev Zundel dzu at
Thu Jun 5 02:30:50 EST 2008

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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