What happens when KMS fails?
closed as not a real question by Tom Brossman, Uri Herrera, Mitch♦, Takkat, stephenmyall Sep 14 '12 at 14:28
It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center.If this question can be reworded to fit the rules in the help center, please edit the question.
Mode setting is basically setting up the screen resolution and the depth mode for the graphics card.
If KMS were to fail, I would think that X would do its own modesetting; instead of having the kernel do it. But that might require you to first disable KMS. More information specifically for different graphics gards can be found on the Ubuntu Wiki article I linked to eariler.