Current support and roadmap for discrete graphics card hot switching

[Albert Vilella]

>
> There is no support, and AFAIK no roadmap either. There are many
>> technical reasons why this is not possible today. In short, I wouldn't
>> suggest getting a dual GPU laptop with the purpose of using it under
>> linux, as one of the GPUs will probably stay unused.
>
>
Just to clarify the current situation: in some laptops, like Sony Vaio
models (SZ-series, Z-series), this feature is "partially" working:

One can do a cold reboot: using the hardware stamina/speed switch in the
laptop to switch off the discrete
graphics card (Nvidia) at BIOS time. But the latest models (Z-series) allow
for a hot switch, right now only in Windows Vista.
If one installs Linux on these, both the Nvidia and the Intel will appear in
lspci, but xorg will not be able to handle both,
and the Nvidia hardware will be wasting battery and not being used.
Some people has managed to revert back to the cold reboot feature by
installing Windows XP on the laptop,
then switching on/off the discrete graphics card at BIOS time.

So the next step is the hot switch. My hunch is that Windows Vista does some
sort of "gdm restart" equivalent,
by the looks of this video on computer.tv:

Jump to 4:10 for the switching bit:

http://www.youtube.com/watch?v=Qcvu2Aluy7g

This machine is the successor of the SZ premium series, and has a Dynamic
Hybrid Graphics system that will enable/disable the nvidia graphics card
using a software "hot" switch instead of a hardware "cold" switch (SZ
series).

http://vaio-online.sony.com/prod_info/series1/z/interview_Z/index_05.html
Can I ask someone who is expert enough in xorg to give a list of
blockers/things to try for this to happen, so that people can play with?
For example, people has been investigating BiosBase on the Nvidia side of
things:

http://avilella.googlepages.com/vaioz (look for BiosBase)
http://bugs.freedesktop.org/show_bug.cgi?id=2597#c37

Thanks,

    Albert.
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