Thank all of you!, I finally unbrick my KPW last night.
I cleared boot counter by following rastik's step and unbrick my KPW.
- attach serial cable
- boot
- immediately after restart enter any key to stop autoboot
- enter "bist" and then "fastboot"
- via fastboot tool flash data and diags partitions on PC(windows or linux), img files is here:
http://snipurl.com/debrick
- reboot
- immediately after restart enter any key to stop autoboot
- enter "run bootargs_diags ; bootm 0xE41000" to boot to diags
- get login prompy (menu "D) Exit, Reboot or Disable Diags" and then "L) Exit to login prompt")
- login as root (password:fiona2bc)
- enter "echo 0 > /var/local/upstart/lab126_gui.restarts"
- reboot
- after a while, press Enter to enter Recovery Menu
- select "E. Export FAT partition" to export U disk
- copy update_kindle_5.3.1.bin to U disk.
- press 1 to back Recovery Menu
- select "U. Update using update*.bin file on FAT partition" to update root partition.
- select "Q. quit" to boot
OK! My KPW is unbricked!