TODO:
- checkpatch.pl fixes
  These checks should be ignored:
    CHECK:ALLOC_SIZEOF_STRUCT: Prefer kmalloc(sizeof(*board->private_data)...) over kmalloc(sizeof(struct xxx_priv)...)
    ./gpio/gpib_bitbang.c:50: ERROR:COMPLEX_MACRO: Macros with complex values should be enclosed in parenthese
  This warning will be addressed later:  WARNING:UNDOCUMENTED_DT_STRING: DT compatible string
- tidy-up comments:
  - there are some "//comments" and "// comments" scattered around
  - sometimes they are misaligned
  - sometimes "// comments" are interleaved with "/* comments */"
  - multiline comments should start with initial almost-blank line:
    /*
     * Good
     * multiline
     * comment
     */
    /* Bad
     * multiline
     * comment
     */
- resolve XXX notes where possible
- fix FIXME notes
- clean-up commented-out code
- fix typos
