What is the test for qualified immunity in the context of a Fourth Amendment violation?

If a genuine issue of fact exists preventing a determination of qualified immunity at summary judgment, the case must proceed to trial. Where a Fourth Amendment violation is claimed, the factual issues that may preclude a determination of qualified immunity on summary judgment fall into two categories. First, a determination of reasonable suspicion or probable cause requires an inquiry as to the facts and circumstances within an officer's knowledge. United States v. Maybusher, 735 F.2d 366, 371 (9th Cir.1984) (reasonable suspicion), cert. denied, 469 U.S. 1110, 105 S.Ct. 790, 83 L.Ed.2d 783 (1985); United States v. Greene, 783 F.2d 1364, 1367 (9th Cir.) (probable cause), cert. denied, 476 U.S. 1185, 106 S.Ct. 2923, 91 L.Ed.2d 551 (1986). These are matters of fact to be determined, where genuine disputes of a material nature exist, by the fact finder. ³ Second, the determination of what conduct underlies the alleged violation--what the officer and claimant did or failed to do--is a determination of fact. We hold, however, that the determination whether those facts support an objective belief that probable cause or reasonable suspicion existed is ordinarily a question for the court. It is not in itself a factual issue that can preclude summary judgment.