In wireless communication, the discovery of the surrounding access points is crucial to provide seamless connectivity to mobile users. In IEEE 802.11, this discovery process is performed by passive and active scanning functions. For both, timers are usually constant (within the 802.11 driver) and their configuration affects the two main scanning performance metrics, i.e., scanning latency and scanning failure. In order to manage this trade-off, we propose a couple of adaptive scanning algorithms that are aware of the access point's signal power and congestion level using cross-layer information from the physical layer. As shown by experimentation in a real testbed, this allows a faster topology discovery while mostly reducing the failure rate.