How to use vgaswitcheroo? doesn't work for me.

Hello,

I'm using 10.10 natty migrated from my old laptop to a just bought Asus N53SN. The problem is not related to my installation because it also happens with LiveCD.

The Asus has two graphics cards, integrated Intel and discrete nVidia, using the so-called "optimus" technology. So:

~$ lspci | grep VGA
00:02.0 VGA compatible controller: Intel Corporation 2nd Generation Core Processor Family Integrated Graphics Controller (rev 09)
01:00.0 VGA compatible controller: nVidia Corporation Device 0df6 (rev a1)

As advertised, the nVidia card is a GT 550M. Now, let's see if we have vgaswitcheroo:
~$ sudo cat /sys/kernel/debug/vgaswitcheroo/switch
0:IGD:+:Pwr:0000:00:02.0
1:DIS: :Pwr:0000:01:00.0

We do. Let's try to switch; first problem is permission:
~$ sudo echo DDIS > /sys/kernel/debug/vgaswitcheroo/switch
bash: /sys/kernel/debug/vgaswitcheroo/switch: Permission denied

But the partition is mounted:
~$ mount | grep /sys/kernel/debug
none on /sys/kernel/debug type debugfs (rw)

Found a way to overcome:
~$ sudo -i
~# echo DDIS > /sys/kernel/debug/vgaswitcheroo/switch
~# cat /sys/kernel/debug/vgaswitcheroo/switch
0:IGD:+:Pwr:0000:00:02.0
1:DIS: :Pwr:0000:01:00.0

But it didn't help, switching doesn't happen. But, if I turn nVidia OFF:
~# echo OFF > /sys/kernel/debug/vgaswitcheroo/switch

HANG! - Keep seeing the screen but everything is frozen: mouse, ctrl-alt-Fx..., only brute-force switch-off works.
So, I'm back; I now had saved this message because I knew it was going to happen as on the first time. It's repeatable.

I searched the answers and bugs databases for "vgaswitcheroo" and found nothing.

Can anybody help to make this work, please?

Rgds
jss