#! /bin/sh
  # SPDX-License-Identifier: GPL-2.0
  # Copyright (c) 2020, Google LLC. All rights reserved.
  # Author: Saravana Kannan <saravanak@google.com>
  
  function help() {
  	cat << EOF
  Usage: $(basename $0) [-c|-d|-m|-f] [filter options] <list of devices>
  
  This script needs to be run on the target device once it has booted to a
  shell.
  
  The script takes as input a list of one or more device directories under
  /sys/devices and then lists the probe dependency chain (suppliers and
  parents) of these devices. It does a breadth first search of the dependency
  chain, so the last entry in the output is close to the root of the
  dependency chain.
  
  By default it lists the full path to the devices under /sys/devices.
  
  It also takes an optional modifier flag as the first parameter to change
  what information is listed in the output. If the requested information is
  not available, the device name is printed.
  
    -c	lists the compatible string of the dependencies
    -d	lists the driver name of the dependencies that have probed
    -m	lists the module name of the dependencies that have a module
    -f	list the firmware node path of the dependencies
    -g	list the dependencies as edges and nodes for graphviz
    -t	list the dependencies as edges for tsort
  
  The filter options provide a way to filter out some dependencies:
    --allow-no-driver	By default dependencies that don't have a driver
  			attached are ignored. This is to avoid following
  			device links to "class" devices that are created
  			when the consumer probes (as in, not a probe
  			dependency). If you want to follow these links
  			anyway, use this flag.
  
    --exclude-devlinks	Don't follow device links when tracking probe
  			dependencies.
  
    --exclude-parents	Don't follow parent devices when tracking probe
  			dependencies.
  
  EOF
  }
  
  function dev_to_detail() {
  	local i=0
  	while [ $i -lt ${#OUT_LIST[@]} ]
  	do
  		local C=${OUT_LIST[i]}
  		local S=${OUT_LIST[i+1]}
  		local D="'$(detail_chosen $C $S)'"
  		if [ ! -z "$D" ]
  		then
  			# This weirdness is needed to work with toybox when
  			# using the -t option.
  			printf '%05u\t%s
  ' ${i} "$D" | tr -d \'
  		fi
  		i=$((i+2))
  	done
  }
  
  function already_seen() {
  	local i=0
  	while [ $i -lt ${#OUT_LIST[@]} ]
  	do
  		if [ "$1" = "${OUT_LIST[$i]}" ]
  		then
  			# if-statement treats 0 (no-error) as true
  			return 0
  		fi
  		i=$(($i+2))
  	done
  
  	# if-statement treats 1 (error) as false
  	return 1
  }
  
  # Return 0 (no-error/true) if parent was added
  function add_parent() {
  
  	if [ ${ALLOW_PARENTS} -eq 0 ]
  	then
  		return 1
  	fi
  
  	local CON=$1
  	# $CON could be a symlink path. So, we need to find the real path and
  	# then go up one level to find the real parent.
  	local PARENT=$(realpath $CON/..)
  
  	while [ ! -e ${PARENT}/driver ]
  	do
  		if [ "$PARENT" = "/sys/devices" ]
  		then
  			return 1
  		fi
  		PARENT=$(realpath $PARENT/..)
  	done
  
  	CONSUMERS+=($PARENT)
  	OUT_LIST+=(${CON} ${PARENT})
  	return 0
  }
  
  # Return 0 (no-error/true) if one or more suppliers were added
  function add_suppliers() {
  	local CON=$1
  	local RET=1
  
  	if [ ${ALLOW_DEVLINKS} -eq 0 ]
  	then
  		return 1
  	fi
  
  	SUPPLIER_LINKS=$(ls -1d $CON/supplier:* 2>/dev/null)
  	for SL in $SUPPLIER_LINKS;
  	do
  		SYNC_STATE=$(cat $SL/sync_state_only)
  
  		# sync_state_only links are proxy dependencies.
  		# They can also have cycles. So, don't follow them.
  		if [ "$SYNC_STATE" != '0' ]
  		then
  			continue
  		fi
  
  		SUPPLIER=$(realpath $SL/supplier)
  
  		if [ ! -e $SUPPLIER/driver -a ${ALLOW_NO_DRIVER} -eq 0 ]
  		then
  			continue
  		fi
  
  		CONSUMERS+=($SUPPLIER)
  		OUT_LIST+=(${CON} ${SUPPLIER})
  		RET=0
  	done
  
  	return $RET
  }
  
  function detail_compat() {
  	f=$1/of_node/compatible
  	if [ -e $f ]
  	then
  		echo -n $(cat $f)
  	else
  		echo -n $1
  	fi
  }
  
  function detail_module() {
  	f=$1/driver/module
  	if [ -e $f ]
  	then
  		echo -n $(basename $(realpath $f))
  	else
  		echo -n $1
  	fi
  }
  
  function detail_driver() {
  	f=$1/driver
  	if [ -e $f ]
  	then
  		echo -n $(basename $(realpath $f))
  	else
  		echo -n $1
  	fi
  }
  
  function detail_fwnode() {
  	f=$1/firmware_node
  	if [ ! -e $f ]
  	then
  		f=$1/of_node
  	fi
  
  	if [ -e $f ]
  	then
  		echo -n $(realpath $f)
  	else
  		echo -n $1
  	fi
  }
  
  function detail_graphviz() {
  	if [ "$2" != "ROOT" ]
  	then
  		echo -n "\"$(basename $2)\"->\"$(basename $1)\""
  	else
  		echo -n "\"$(basename $1)\""
  	fi
  }
  
  function detail_tsort() {
  	echo -n "\"$2\" \"$1\""
  }
  
  function detail_device() { echo -n $1; }
  
  alias detail=detail_device
  ALLOW_NO_DRIVER=0
  ALLOW_DEVLINKS=1
  ALLOW_PARENTS=1
  
  while [ $# -gt 0 ]
  do
  	ARG=$1
  	case $ARG in
  		--help)
  			help
  			exit 0
  			;;
  		-c)
  			alias detail=detail_compat
  			;;
  		-m)
  			alias detail=detail_module
  			;;
  		-d)
  			alias detail=detail_driver
  			;;
  		-f)
  			alias detail=detail_fwnode
  			;;
  		-g)
  			alias detail=detail_graphviz
  			;;
  		-t)
  			alias detail=detail_tsort
  			;;
  		--allow-no-driver)
  			ALLOW_NO_DRIVER=1
  			;;
  		--exclude-devlinks)
  			ALLOW_DEVLINKS=0
  			;;
  		--exclude-parents)
  			ALLOW_PARENTS=0
  			;;
  		*)
  			# Stop at the first argument that's not an option.
  			break
  			;;
  	esac
  	shift
  done
  
  function detail_chosen() {
  	detail $1 $2
  }
  
  if [ $# -eq 0 ]
  then
  	help
  	exit 1
  fi
  
  CONSUMERS=($@)
  OUT_LIST=()
  
  # Do a breadth first, non-recursive tracking of suppliers. The parent is also
  # considered a "supplier" as a device can't probe without its parent.
  i=0
  while [ $i -lt ${#CONSUMERS[@]} ]
  do
  	CONSUMER=$(realpath ${CONSUMERS[$i]})
  	i=$(($i+1))
  
  	if already_seen ${CONSUMER}
  	then
  		continue
  	fi
  
  	# If this is not a device with a driver, we don't care about its
  	# suppliers.
  	if [ ! -e ${CONSUMER}/driver -a ${ALLOW_NO_DRIVER} -eq 0 ]
  	then
  		continue
  	fi
  
  	ROOT=1
  
  	# Add suppliers to CONSUMERS list and output the consumer details.
  	#
  	# We don't need to worry about a cycle in the dependency chain causing
  	# infinite loops. That's because the kernel doesn't allow cycles in
  	# device links unless it's a sync_state_only device link. And we ignore
  	# sync_state_only device links inside add_suppliers.
  	if add_suppliers ${CONSUMER}
  	then
  		ROOT=0
  	fi
  
  	if add_parent ${CONSUMER}
  	then
  		ROOT=0
  	fi
  
  	if [ $ROOT -eq 1 ]
  	then
  		OUT_LIST+=(${CONSUMER} "ROOT")
  	fi
  done
  
  # Can NOT combine sort and uniq using sort -suk2 because stable sort in toybox
  # isn't really stable.
  dev_to_detail | sort -k2 -k1 | uniq -f 1 | sort | cut -f2-
  
  exit 0