Documentation/features: Add script that refreshes the arch support status files in place

Provides the script:

	Documentation/features/scripts/features-refresh.sh

which operates on the arch-support.txt files and refreshes them in place.

This way [1],

   "[...] we soft- decouple the refreshing of the entries from the
    introduction of the features, while still making it all easy to
    keep sync and to extend."

[1] http://lkml.kernel.org/r/20180328122211.GA25420@andreaSuggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/features/scripts/features-refresh.sh

+#
+# Small script that refreshes the kernel feature support status in place.
+#
+
+for F_FILE in Documentation/features/*/*/arch-support.txt; do
+	F=$(grep "^#         Kconfig:" "$F_FILE" | cut -c26-)
+
+	#
+	# Each feature F is identified by a pair (O, K), where 'O' can
+	# be either the empty string (for 'nop') or "not" (the logical
+	# negation operator '!'); other operators are not supported.
+	#
+	O=""
+	K=$F
+	if [[ "$F" == !* ]]; then
+		O="not"
+		K=$(echo $F | sed -e 's/^!//g')
+	fi
+
+	#
+	# F := (O, K) is 'valid' iff there is a Kconfig file (for some
+	# arch) which contains K.
+	#
+	# Notice that this definition entails an 'asymmetry' between
+	# the case 'O = ""' and the case 'O = "not"'. E.g., F may be
+	# _invalid_ if:
+	#
+	# [case 'O = ""']
+	#   1) no arch provides support for F,
+	#   2) K does not exist (e.g., it was renamed/mis-typed);
+	#
+	# [case 'O = "not"']
+	#   3) all archs provide support for F,
+	#   4) as in (2).
+	#
+	# The rationale for adopting this definition (and, thus, for
+	# keeping the asymmetry) is:
+	#
+	#       We want to be able to 'detect' (2) (or (4)).
+	#
+	# (1) and (3) may further warn the developers about the fact
+	# that K can be removed.
+	#
+	F_VALID="false"
+	for ARCH_DIR in arch/*/; do
+		K_FILES=$(find $ARCH_DIR -name "Kconfig*")
+		K_GREP=$(grep "$K" $K_FILES)
+		if [ ! -z "$K_GREP" ]; then
+			F_VALID="true"
+			break
+		fi
+	done
+	if [ "$F_VALID" = "false" ]; then
+		printf "WARNING: '%s' is not a valid Kconfig\n" "$F"
+	fi
+
+	T_FILE="$F_FILE.tmp"
+	grep "^#" $F_FILE > $T_FILE
+	echo "    -----------------------" >> $T_FILE
+	echo "    |         arch |status|" >> $T_FILE
+	echo "    -----------------------" >> $T_FILE
+	for ARCH_DIR in arch/*/; do
+		ARCH=$(echo $ARCH_DIR | sed -e 's/arch//g' | sed -e 's/\///g')
+		K_FILES=$(find $ARCH_DIR -name "Kconfig*")
+		K_GREP=$(grep "$K" $K_FILES)
+		#
+		# Arch support status values for (O, K) are updated according
+		# to the following rules.
+		#
+		#   - ("", K) is 'supported by a given arch', if there is a
+		#     Kconfig file for that arch which contains K;
+		#
+		#   - ("not", K) is 'supported by a given arch', if there is
+		#     no Kconfig file for that arch which contains K;
+		#
+		#   - otherwise: preserve the previous status value (if any),
+		#                default to 'not yet supported'.
+		#
+		# Notice that, according these rules, invalid features may be
+		# updated/modified.
+		#
+		if [ "$O" = "" ] && [ ! -z "$K_GREP" ]; then
+			printf "    |%12s: |  ok  |\n" "$ARCH" >> $T_FILE
+		elif [ "$O" = "not" ] && [ -z "$K_GREP" ]; then
+			printf "    |%12s: |  ok  |\n" "$ARCH" >> $T_FILE
+		else
+			S=$(grep -v "^#" "$F_FILE" | grep " $ARCH:")
+			if [ ! -z "$S" ]; then
+				echo "$S" >> $T_FILE
+			else
+				printf "    |%12s: | TODO |\n" "$ARCH" \
+					>> $T_FILE
+			fi
+		fi
+	done
+	echo "    -----------------------" >> $T_FILE
+	mv $T_FILE $F_FILE
+done