EXA & vtSema

[Jon Smirl]

The fun rules of VT swap are that the swap can do anything it wants to
the hardware. That includes resetting it, turning off the GPU, wiping
VRAM, disabling it's PCI IO/MEM access, etc. When you get swapped back
you have to recover from all of these things.

For example a framebuffer driver can not leave interrupts running
across a VT swap. I found out the hard way (my machine locked on VT
swap) that X is going to turn off the PCI IO/MEM access and my ISR
then isn't able to ack the interrupt because it can't write to the
registers.

You can get away with not restoring some things on a swap. That's
because there are some unwritten agreements between various pairs of X
and fbdev drivers to not stomp on certain registers or parts of
memory.

-- 
Jon Smirl
jonsmirl at gmail.com