Disabling drm/ttm/radeon module loading for debugging

[Pasi Kärkkäinen]

On Sun, Jan 24, 2010 at 07:07:22AM +1000, Dave Airlie wrote:
> On Sat, 2010-01-23 at 18:49 +0200, Pasi Kärkkäinen wrote:
> > On Sat, Jan 23, 2010 at 11:41:15AM -0500, Clyde E. Kunkel wrote:
> > > On 01/23/2010 09:08 AM, Pasi Kärkkäinen wrote:
> > >> Hello,
> > >>
> > >> How can I make sure drm/radeon/ttm modules are not loaded,
> > >> until I do it manually myself?
> > >>
> > >> I extracted the initrd image, edited the 'init' script and
> > >> commented out loading of the modules, repacked the initrd,
> > >> and booted but something (plymouth? udev?) still loads the modules..
> > >>
> > >> I'd like to load them later manually, for some debugging purposes..
> > >>
> > >> -- Pasi
> > >>
> > >
> > > Try adding nomodeset to the kernel line in grub.conf.
> > >
> > 
> > Sorry forgot to mention that I already have nomodeset..
> > It seems it's not enough.
> 
> You should be able to rmmod them with nomodeset, the driver
> doesn't do any initialisation in that case. though you
> should boot to runlevel 3 as once X starts the hw will
> be initialised.
> 
> Then you need to load radeon with modeset=1 to override it.
> 

What I'm trying to do here is to debug some kind of text 'offset' 
problem when the kernel is booted as Xen dom0, under the hypervisor.

I just tried booting the kernel on baremetal, without Xen.

It seems something is initialized when the drivers are loaded 
for the first time (automatically by most probably udev, 
trying to blacklist them now and see if that prevents them 
from being loaded), because there's a small 'flash' on the screen
when udev is started. This 'flash' happens on baremetal.

When booting the same kernel binary as Xen dom0, I get weird 
'offset' to every line of text when drm/radeon/ttm modules are loaded.. 
(this offset thing happens at the same moment when there's the 
'flash' on baremetal).

The beginning of every line moves from the left edge of the screen 
to 1/4 of the screen.. and the end of each line wraps to the beginning of
next line. It's a bit difficult to read the screen :) 

Anyway, I want to make sure drm/radeon/ttm drivers are not loaded 
automatically so I can load them manually and debug what exactly happens.

Video of the boot process here, showing the "offset" problem:
http://pasik.reaktio.net/xen/pv_ops-dom0-debug/xen_pvops_dom0_vga_console_line_offset_problem-xvid.avi

Same kernel binary doesnt' have the "offset" problem when booted on 
baremetal, so it's some kind of issue when the kernel is ran under the hypervisor.

Kernel is version 2.6.31.6.

-- Pasi