Display driver power management


Here i have a very tricky question.
I m trying my best to implement to display driver that it only sends
data to display, when if image in wince frame buffer has changed.
here i would like to know this generic question
If no new blits is received from the GDI,then we have to intimate
kernel to enter sleep mode.??
Let me know your views on above scenario... how to find the correct
functions in GPE classes. to get to know the blit changes.