Have you ever wanted to use the GENMASK or GENMASK_ULL macros from the linux kernels bits.h file? Yeah, me neither, but when working with hardware drivers handling bitmasks is quite common when extracting or changing certain bits in registers and depending on where you look and who you ask the use of the GENMASK macro-family is sometimes prefered over good old 0xffc hex literals.
However I found the specific meaning of the h and l parameter of these macros to be, let's say, under-document and not obvious, so I wrote a small online calculator that helps me out: https://mazdermind.de/genmask/ and I hope it will also help you.
That's it, good luck with your driver and have fun tinkering around.