First patch is to add file-backed implementation to allow users to assign
an OTP image file to machine. Users can assign the property, "otp-file",
to machine to enable it. File-backed feature is set to "NULL" string in
default. Any filename other than "NULL" is used as OTP image file.

For example, '-M sifive_u,otp-file="otp.img"'

To keep data up-to-date due to an unexpected crash or CTRL+a-x exit, every
read/write command to OTP memory involves file open, mmap and close
operation to the image file.

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.

Tested on sifive_u for both qemu and u-boot.

Green Wan (2):
  hw/riscv: sifive_u: Add file-backed OTP.
  hw/riscv: sifive_u: Add write-once protection.

 hw/riscv/sifive_u.c             |  26 ++++++++
 hw/riscv/sifive_u_otp.c         | 103 ++++++++++++++++++++++++++++++++
 include/hw/riscv/sifive_u.h     |   2 +
 include/hw/riscv/sifive_u_otp.h |   2 +
 4 files changed, 133 insertions(+)

-- 
2.17.1