Many years ago, right enough, I was told that the aim was a chisel edge.......two different degrees.
Mmmm, well, don't know about that. For carving, I'd find that kind of edge useless. If I get a carving knife and it has a secondary bevel, it goes in the drawer until I get time to get rid of it. Micro bevel yes, secondary bevel, no. At least for carving. For utility and hard use, that's another strory.
These are some of my carving knives, All are flat, flat, flat. You can keep 'em sharp simply by stropping. They will develop a convex bevel after awhile because of the give in a strop. I don't mind a convex microbevel but when it gets to be too much, I have to flatten the blades again.
Rick Ferry is quite a famous carver and runs Little Shavers. He also sharpens carving knives for carvers around the world. I think he once said he's sharpened over 7,000 knives. He has a great page
here on sharpening.
With the exception of the knife on the lower left, all of these whittlers have blades that are flat with no secondary bevel.
Like the carvers above, the blades are really thin. They are designed for carving woods like basswood. The blades on the folder on the lower left are flat ground with a bit of a convex edge. That knife is set up for cutting hardwoods like walnut. Del Stub's knives work well for hardwoods too (second from left, top photo), and they are flat ground but with thicker blades than the others. So the angle of the primary bevel makes a difference as well.