powerpc: udbg based backend for hvc_console

[Timur Tabi]

Milton Miller wrote:

> We want the last console= parameter on the command line to win.  So if 
> that implys the last call to add_preferred_console wins, then you have 
> code overriding the command line.

Hmm, good point.  However, how likely is it that we'll have more than one
console driver?  Also, without calling add_preferred_console(), the kernel needs
to have a console= on the command line.

In my case, my driver only calls add_preferred_console() if the device tree
contains a specific property that it looks for.  In effect, this property
override the console= line.  However, the console= line goes to the HVC
subsystem, and not my driver, and I can't use it to send the configuration data
the driver needs.

Unfortunately, my driver hasn't been published yet, so it's hard to explain the
details.  I guess I need to think about this more.

-- 
Timur Tabi
Linux kernel developer at Freescale