Once you have performed a mapping (via one of the just-covered [devm_]ioremap*()APIs), it can actually be seen via the read-only pseudo-file; that is, /proc/iomem. The reality is that a new entry under /proc/iomem is generated when you successfully call request_mem_region(). Viewing it requires root access (more correctly, you can view it as non-root but will only see all the addresses as 0; this is for security purposes). So, let's take a look at this on our trusty x86_64 Ubuntu guest VM. In the following output, due to lack of space and for clarity, we'll show it partially truncated:
$ sudo cat /proc/iomem
[sudo] password for llkd:
00000000-00000fff : Reserved
00001000-0009fbff : System RAM
0009fc00-0009ffff : Reserved
000a0000-000bffff : PCI Bus 0000:00
000c0000-000c7fff : Video ROM
000e2000-000ef3ff : Adapter ROM
000f0000-000fffff : Reserved
000f0000-000fffff : System ROM
00100000-3ffeffff : System RAM
18800000-194031d0...
