Based RFC v3 to fix:
 - Fix all nits-related
 - Use blk for blk_by_legacy_dinfo(dinfo) 
 - Move SET_WRITTEN_BIT out from else branch

Summary of Patches
 - First patch is to add file-backed implementation to allow users to use
   '-drive' to assign an OTP raw image file. OTP image file must be bigger
   than 16K.

       For example, '-drive if=none,format=raw,file=otp.img'

 - Second patch is to add 'write-once' feature to block second write to
   the OTP memory. Only keep the 'written' state for non-control register
   range from 0x38 to 16KB.

Testing
 - Tested on sifive_u for both qemu and u-boot.

Green Wan (2):
  hw/riscv: sifive_u: Add backend drive support
  hw/riscv: sifive_u: Add write-once protection

 hw/riscv/sifive_u_otp.c         | 71 +++++++++++++++++++++++++++++++++
 include/hw/riscv/sifive_u_otp.h |  3 ++
 2 files changed, 74 insertions(+)

-- 
2.17.1