Patching h700 panel values on device

patch.sh

#/bin/bash

# NOTE: requires dtc to be somewhere in your path

cd "$(dirname "$0")"

# const
DT_NAME=device
DEV_PATH=/dev/mmcblk0
BOOT_OFFSET=$((16400 * 1024))
DTB_OFFSET=$((BOOT_OFFSET+1161216))
SIZE_OFFSET=$((DTB_OFFSET+4))

# var
DTB_SIZE=$((0x`xxd -s $SIZE_OFFSET -l 4 -ps $DEV_PATH`))

dd if=$DEV_PATH of=$DT_NAME.dtb bs=1 skip=$DTB_OFFSET count=$DTB_SIZE 2>/dev/null # extract
dtc -I dtb -O dts -o $DT_NAME.dts $DT_NAME.dtb 2>/dev/null # decompile

if [ ! -f $DT_NAME.dts ]; then
	echo "unable to decompile dtb, aborting"
	exit 1
fi

# cat $DT_NAME.dts | grep 'lcd_backlight\|lcd_ht\|lcd_vt\|lcd_dclk_freq'

CF= # lcd_dclk_freq
HT= # lcd_ht
VT= # lcd_vt
BL= # lcd_backlight

# parse the values out of the decompiled dtb
while read -r LINE; do
    KEY=$(echo "$LINE" | grep -oP '^[\w_]+')
    HEX=$(echo "$LINE" | grep -oP '0x[\dA-Fa-f]+')
	DEC=$(($HEX))

	case $KEY in
	lcd_dclk_freq)
		CF=$DEC
		;;
	lcd_ht)
		HT=$DEC
		;;
	lcd_vt)
		VT=$DEC
		;;
	lcd_backlight)
		BL=$DEC
		;;
	esac
# redirect instead of using a pipe so variables stay in scope
done < <(grep 'lcd_backlight\|lcd_dclk_freq\|lcd_ht\|lcd_vt' "$DT_NAME.dts")

echo "    CF HT  VT  (BL)"
echo "IN  $CF-$HT-$VT ($BL)"

# match to known (incorrect) values
HT_OFFSET=0
VT_OFFSET=0
case $CF-$HT-$VT in
24-770-526) # 35xx2024/35xxPLUS
	HT_OFFSET=-2 # 768
	VT_OFFSET=-5 # 521
	;;
24-770-528) # 35xxH
	HT_OFFSET=-2 # 768
	VT_OFFSET=-7 # 521
	;;
24-586-686) # 28xx
	HT_OFFSET=-2 # 584
	VT_OFFSET=-1 # 685
	;;
24-770-525) # 35xxSP
	HT_OFFSET=-2 # 768
	VT_OFFSET=-4 # 521
	;;
24-770-522) # 40xxH
	HT_OFFSET=-2 # 768
	VT_OFFSET=-1 # 521
	;;
esac

# update values or bail
BL_OFFSET=$((HT_OFFSET+VT_OFFSET))
if [ $BL_OFFSET -ne 0 ]; then
	HT=$((HT+HT_OFFSET))
	VT=$((VT+VT_OFFSET))
	BL=$((BL-BL_OFFSET))
else
	echo "unrecognized panel configuration, aborting"
	exit 0
fi

echo "OUT $CF-$HT-$VT ($BL)"

# dupe and inject updated values
MOD_PATH=$DT_NAME-mod.dts
cp $DT_NAME.dts $MOD_PATH
sed -i "s/\(lcd_ht = <\)0x[0-9A-Fa-f]\+/\1$HT/" "$MOD_PATH"
sed -i "s/\(lcd_vt = <\)0x[0-9A-Fa-f]\+/\1$VT/" "$MOD_PATH"
sed -i "s/\(lcd_backlight = <\)0x[0-9A-Fa-f]\+/\1$BL/" "$MOD_PATH"

# cat $MOD_PATH | grep 'lcd_backlight\|lcd_dclk_freq\|lcd_ht\|lcd_vt'

dtc -I dts -O dtb -o $DT_NAME-mod.dtb $DT_NAME-mod.dts 2>/dev/null # recompile
dd if=$DT_NAME.dtb of=$DT_NAME-mod.dtb bs=1 skip=4 seek=4 count=4 conv=notrunc 2>/dev/null # inject original size
fallocate -l $DTB_SIZE $DT_NAME-mod.dtb # zero fill empty space

# validate checksum
A_PATH=$DT_NAME.dtb
B_PATH=$DT_NAME-mod.dtb

declare -a BYTES
BYTES=(`xxd -p -c 1 $A_PATH | tr '\n' ' '`)
SUM=0
for (( i=0; i<${#BYTES[@]}; i++)); do
	SUM=$((SUM+0x${BYTES[i]}))
done
A_SUM=$SUM

declare -a BYTES
BYTES=(`xxd -p -c 1 $B_PATH | tr '\n' ' '`)
SUM=0
for (( i=0; i<${#BYTES[@]}; i++)); do
	SUM=$((SUM+0x${BYTES[i]}))
done
B_SUM=$SUM

if [ $A_SUM != $B_SUM ]; then
	echo "A $A_SUM"
	echo "B $B_SUM"
	echo "mismatched checksum, aborting"
	exit 1
fi

dd if=$DT_NAME-mod.dtb of=$DEV_PATH bs=1 seek=$DTB_OFFSET conv=notrunc 2>/dev/null # inject

echo "patched successfully!"