Is clamping a valid termination strategy?
When advanced low Vdd CMOS uses RdsOn of 25 Ohms at 3.3V with 0.2 to 2 ns rise times, designers often are unaware of need to have controlled impedance tracks and results in ringing at half wavelength of track length.


low power Schottky diodes with small capacitance are sometimes used to provide a dynamic load impedance of around this driver impedance range to at least provide some matched load to the overshoot.
when the transmission line is mostly inductive
from poor coupling to gnd tracks or gnd plane near same gap as track width, and with CMOS input Z can be x pF and 1GOhm, ringing and UNDERSHOOT can cause glitches. 


analogy

The clamp diodes are like a stiffer rubber end stop to a spring (inductive track) with a weak shock absorber in zero gravity going over a pot hole and the car still bottoms out and then jumps up but with less bouncing shock waves. A properly tuned shock absorber is like a properly tuned transmission line to give controlled step response with minimal overshoot/undershoot and ringing.

No overshoot is a theoretical perfect transmission line matched to between source and terminator which is as I said above can be 25 ohms -/+50% with temp and 10% supply variation. so often terminated with 50 Ohms. with tracks matching the load. But skin effects and dynamic dielectric constant reduction >1Ghz causes some imperfections .

A diode is a poor man's choice for lack of impedance controlled on track layout and design,pick any; coplanar, stripline, microstrip! for 50 Ohm single ended and 100 Ohm differential.