[soft-reboot] Add support for platforms based on Device Tree (sonic-net#1963)

What I did
Add soft-reboot command support for the armhf and arm64 platforms

How I did it
Add logic to retrieve kernel boot arguments from the Device Tree rather than from the GRUB config for these platforms

How to verify it
Execute the soft-reboot command on an armhf or arm64 platform

Author: dflynn-Nokia

scripts/soft-reboot

@@ -117,15 +117,33 @@ function setup_reboot_variables()
     if grep -q aboot_platform= /host/machine.conf; then
         KERNEL_IMAGE="$(ls $IMAGE_PATH/boot/vmlinuz-*)"
         BOOT_OPTIONS="$(cat "$IMAGE_PATH/kernel-cmdline" | tr '\n' ' ') SONIC_BOOT_TYPE=${BOOT_TYPE_ARG}"
+        INITRD=$(echo $KERNEL_IMAGE | sed 's/vmlinuz/initrd.img/g')
     elif grep -q onie_platform= /host/machine.conf; then
-        KERNEL_OPTIONS=$(cat /host/grub/grub.cfg | sed "/$NEXT_SONIC_IMAGE'/,/}/"'!'"g" | grep linux)
-        KERNEL_IMAGE="/host$(echo $KERNEL_OPTIONS | cut -d ' ' -f 2)"
-        BOOT_OPTIONS="$(echo $KERNEL_OPTIONS | sed -e 's/\s*linux\s*/BOOT_IMAGE=/') SONIC_BOOT_TYPE=${BOOT_TYPE_ARG}"
+        if [ -r /host/grub/grub.cfg ]; then
+            KERNEL_OPTIONS=$(cat /host/grub/grub.cfg | sed "/$NEXT_SONIC_IMAGE'/,/}/"'!'"g" | grep linux)
+            KERNEL_IMAGE="/host$(echo $KERNEL_OPTIONS | cut -d ' ' -f 2)"
+            BOOT_OPTIONS="$(echo $KERNEL_OPTIONS | sed -e 's/\s*linux\s*/BOOT_IMAGE=/') SONIC_BOOT_TYPE=${BOOT_TYPE_ARG}"
+            INITRD=$(echo $KERNEL_IMAGE | sed 's/vmlinuz/initrd.img/g')
+        # Handle architectures supporting Device Tree
+        elif [ -f /sys/firmware/devicetree/base/chosen/bootargs ]; then
+            KERNEL_IMAGE="$(ls $IMAGE_PATH/boot/vmlinuz-*)"
+            BOOT_OPTIONS="$(cat /sys/firmware/devicetree/base/chosen/bootargs | sed 's/.$//') SONIC_BOOT_TYPE=${BOOT_TYPE_ARG}"
+            INITRD=$(echo $KERNEL_IMAGE | sed 's/vmlinuz/initrd.img/g')
+
+            # If initrd is a U-Boot uImage, remove the uImage header
+            if file ${INITRD} | grep -q uImage; then
+                INITRD_RAW=$(echo $KERNEL_IMAGE | sed 's/vmlinuz/initrd-raw.img/g')
+                tail -c+65 < ${INITRD} > ${INITRD_RAW}
+                INITRD=${INITRD_RAW}
+            fi
+        else
+            error "Unknown ONIE platform bootloader. ${REBOOT_TYPE} is not supported."
+            exit "${EXIT_NOT_SUPPORTED}"
+        fi
     else
         error "Unknown bootloader. ${REBOOT_TYPE} is not supported."
         exit "${EXIT_NOT_SUPPORTED}"
     fi
-    INITRD=$(echo $KERNEL_IMAGE | sed 's/vmlinuz/initrd.img/g')
 }
 
 function load_kernel() {