Some months ago, David Airlie wrote VGA switcheroo as a system to enable hybrid graphics hot switching via logout/login from a X session.
David initially implemented this on an ATI hybrid laptop, but immediately after the first implementation, with Matthew Garrett's help, he also committed some code to enable it on nvidia hybrid configurations. This wasn't thoroughly tested at the time due to the lack of hardware, but different users in the hybrid-graphics-linux launchpad team have reported their success stories with VGA switcheroo.
Compared to VGA switcheroo, acpi_call is a module to test what ACPI method is available to switch on/off the discrete graphics card. Many nvidia laptop configurations have different ACPI methods, so in order to switch on/off the nvidia card, one needs to call the right method for the laptop.
It is in theory possible to put together the work done on acpi_call and VGA switcheroo, so that most of the laptop configurations would have the hot switching feature via logout/login in Linux. There is a bit of work to be done in code integration, hopefully someone will pick this up and work on it, since there are now more than 200 users who would benefit from it.
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