Is it a defined bike trail with a defined direction? If not, you can try and chat but otherwise it is a free-for-all on going up or down.
Can’t remember the code (maybe driving a vehicle), but I’m sure people going up have right of way (thinking is that it is harder to start going up than down) – kills a downhill but you should be riding to the conditions and all that.
Started a mild rant so I’ll stop but will repeat, if it is a designated trail with a specified one-way only direction, then they have the same right to go up as you have to go down. Part of the joy of the great outdoors, others use it as well.
Saying that, if I know a trail is used mainly as a downhill then I tend to avoid riding up – so although I’m sounding all holier-than-thou, I’d also be a bit annoyed if people were not being careful on their way up.