How to load amd64-microcode firmware

Installing and Using OpenWrt
1

I am running on x64-64 with AMD hardware. I have the amd64-microcode package installed but I don't find any evidence that it is getting loaded at boot. For example, before installing the package:

grep -i microcode /proc/cpuinfo
microcode	: 0xa50000d
microcode	: 0xa50000d
microcode	: 0xa50000d
microcode	: 0xa50000d
microcode	: 0xa50000d
microcode	: 0xa50000d
microcode	: 0xa50000d
microcode	: 0xa50000d
microcode	: 0xa50000d
microcode	: 0xa50000d
microcode	: 0xa50000d
microcode	: 0xa50000d
microcode	: 0xa50000d
microcode	: 0xa50000d
microcode	: 0xa50000d
microcode	: 0xa50000d

The output of that command is identical after installing and rebooting.

On my Arch box, the microcode is loaded in grub.cfg with the initrd image, but OpenWRT's grub package is not using that...

# cat /boot/boot/grub/grub.cfg 
serial --unit=0 --speed=115200 --word=8 --parity=no --stop=1 --rtscts=off
terminal_input console serial; terminal_output console serial

set default="0"
set timeout="1"
search -l kernel -s root

menuentry "OpenWrt" {
	linux /boot/vmlinuz root=PARTUUID=7fe1d9bc-6bf4-44dc-b869-b213c3af5102 rootwait  console=tty0 console=ttyS0,115200n8 noinitrd amd_pstate=passive
}
menuentry "OpenWrt (failsafe)" {
	linux /boot/vmlinuz failsafe=true root=PARTUUID=7fe1d9bc-6bf4-44dc-b869-b213c3af5102 rootwait  console=tty0 console=ttyS0,115200n8 noinitrd
}

EDIT: it seems OW is using late loading, (section 1.3):

CONFIG_MICROCODE=y
CONFIG_MICROCODE_INTEL=y
CONFIG_MICROCODE_AMD=y
CONFIG_MICROCODE_LATE_LOADING=y

Yet, when I try to get the firmware to load, I see no difference:

# echo 1 > /sys/devices/system/cpu/microcode/reload
# grep microcode /proc/cpuinfo

microcode	: 0xa50000d
microcode	: 0xa50000d
microcode	: 0xa50000d
microcode	: 0xa50000d
microcode	: 0xa50000d
microcode	: 0xa50000d
microcode	: 0xa50000d
microcode	: 0xa50000d
microcode	: 0xa50000d
microcode	: 0xa50000d
microcode	: 0xa50000d
microcode	: 0xa50000d
microcode	: 0xa50000d
microcode	: 0xa50000d
microcode	: 0xa50000d
microcode	: 0xa50000d
2

I booted to Arch Linux on the same device which uses the early load method:

menuentry "arch1" {
  set root='hd0,gpt3'
  insmod gzio
  insmod part_gpt
  insmod ext2
  linux /boot/vmlinuz-linux root=UUID=06834425-8796-4bfe-b2ec-23d551c8f78d rw audit=0
  initrd  /boot/amd-ucode.img /boot/initramfs-linux.img
}

The microcode version there matches what OpenWrt is using so I am concluding that OW's package is working. It would be nice is dmesg would record something upon running the late load update command.