generic memory addresses

[Tobin C. Harding]

Why is there code in-tree that declares generic memory addresses as
unsigned int?

Linux Device Drivers 3rd Edition page 289
 Therefore, generic memory addresses in the kernel are usually unsigned
 long, exploiting the fact that pointers and long integers are always
 the same size, at least on all the platforms currently supported by
 Linux.

It would therefore seem like a bug to declare a generic memory address
as an unsigned int in code that can run on 64 bit machines.

What is the explanation for such declarations in the kernel please?

$ cd KERNEL_TREE
$ git grep 'unsigned int addr' | wc -l
556

thanks,
Tobin.