I found the following documents.
Command description
https://github.com/espressif/esptool/wiki/Advanced-Commands#write_flash_status
Source code
https://github.com/espressif/esptool/blob/master/esptool.py
L3499
def write_flash_status(esp, args)
GD25Q32C datasheet
http://www.elm-tech.com/ja/products/spi-flash-memory/gd25q32/gd25q32.pdf