Current support and roadmap for discrete graphics card hot switching

[Roland Scheidegger]

On 15.01.2009 13:04, Stephane Marchesin wrote:
> Basically, we lack :
> - documentation on how to switch GPUs at the laptop level (i.e. do
> what the bios does at boot when you choose the card in the bios)
> - documentation on cold booting the nvidia GPU
> - driver support on both sides implementing proper GPU power up/shut down
> (we're talking about something big here)
I always wondered how this works at the hardware level. How are the
chips shut off? I guess for the external chip what you really want to do
is cut power completely - is this somehow standardized, can you do that
through ACPI? How are the outputs switched - some (external to the
graphic chips) multiplexers or what, again controlled by ACPI bios?
Isn't power up quite similar to just regular posting of the chip?


> 
> and if you want to keep your session in between, we lack
> - X.Org infrastructure to hand a session from a graphics driver to
> another (there are a million of possible problems here)
> - drivers supporting said infrastructure
> (we're talking about something real huge here)
> 
> IMO all this is not very likely to happen.
Yes, keeping the session sounds very complicated (though that's probably
what people want, for most it probably wouldn't make a difference
between rebooting or just restarting X). For the manual switch, I'm not
sure how complicated that really would be - of course lacking
documentation would be a problem.

> When you buy a laptop on
> which you want to run linux, I really suggest you check hardware
> compatibility. This is no different than unsupported wifi chips.
Well, for WiFi chips there's always the hope it will be supported in the
future :-).

Roland