MIPS: generic: Allow filtering enabled boards by requirements

Up until now when configuring a generic kernel all board config
fragments have been merged by default unless boards are explicitly
selected by the user specifying BOARDS=.

In many cases this is sub-optimal, since some boards don't make sense to
include in some kernels. For example the MIPS SEAD-3 development board
has only ever been used with 32 bit CPUs, so including support for the
SEAD-3 in a 64 bit kernel is wasteful.

This patch introduces support for specifying requirements in board
config fragments, using comments formatted like so:

  # require CONFIG_BLA=y

For example the SEAD-3 board could specify that it should only be merged
for 32 bit kernels using a requirement line like the following:

  # require CONFIG_32BIT=y

A new generic-board-config.sh script is introduced to handle selecting
the board config fragments to merge & calling merge_config.sh to merge
them. In order to allow requirements to check Kconfig symbols that are
implicitly selected, rather than explicitly specified by
generic_defconfig or one of the ISA config fragments, an intermediate
.config file is saved & used as a reference when checking requirements.
Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/16943/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

MAINTAINERS

@@ -8792,6 +8792,7 @@ M:	Paul Burton <paul.burton@imgtec.com>
 L:	linux-mips@linux-mips.org
 S:	Supported
 F:	arch/mips/generic/
+F:	arch/mips/tools/generic-board-config.sh
 
 MIPS/LOONGSON1 ARCHITECTURE
 M:	Keguang Zhang <keguang.zhang@gmail.com>

arch/mips/Makefile

@@ -500,8 +500,14 @@ $(eval $(call gen_generic_defconfigs,micro32,r2,eb el))
 .PHONY: $(generic_defconfigs)
 $(generic_defconfigs):
 	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/kconfig/merge_config.sh \
-		-m -O $(objtree) $(srctree)/arch/$(ARCH)/configs/generic_defconfig $^ \
-		$(foreach board,$(BOARDS),$(generic_config_dir)/board-$(board).config)
+		-m -O $(objtree) $(srctree)/arch/$(ARCH)/configs/generic_defconfig $^ | \
+		grep -Ev '^#'
+	$(Q)cp $(KCONFIG_CONFIG) $(objtree)/.config.$@
+	$(Q)$(MAKE) -f $(srctree)/Makefile olddefconfig \
+		KCONFIG_CONFIG=$(objtree)/.config.$@ >/dev/null
+	$(Q)$(CONFIG_SHELL) $(srctree)/arch/$(ARCH)/tools/generic-board-config.sh \
+		$(srctree) $(objtree) $(objtree)/.config.$@ $(KCONFIG_CONFIG) \
+		"$(origin BOARDS)" $(BOARDS)
 	$(Q)$(MAKE) -f $(srctree)/Makefile olddefconfig
 
 #

arch/mips/tools/generic-board-config.sh

+#!/bin/sh
+#
+# Copyright (C) 2017 Imagination Technologies
+# Author: Paul Burton <paul.burton@imgtec.com>
+#
+# This program is free software; you can redistribute it and/or modify it
+# under the terms of the GNU General Public License as published by the
+# Free Software Foundation;  either version 2 of the  License, or (at your
+# option) any later version.
+#
+# This script merges configuration fragments for boards supported by the
+# generic MIPS kernel. It checks each for requirements specified using
+# formatted comments, and then calls merge_config.sh to merge those
+# fragments which have no unmet requirements.
+#
+# An example of requirements in your board config fragment might be:
+#
+# # require CONFIG_CPU_MIPS32_R2=y
+# # require CONFIG_CPU_LITTLE_ENDIAN=y
+#
+# This would mean that your board is only included in kernels which are
+# configured for little endian MIPS32r2 CPUs, and not for example in kernels
+# configured for 64 bit or big endian systems.
+#
+
+srctree="$1"
+objtree="$2"
+ref_cfg="$3"
+cfg="$4"
+boards_origin="$5"
+shift 5
+
+cd "${srctree}"
+
+# Only print Skipping... lines if the user explicitly specified BOARDS=. In the
+# general case it only serves to obscure the useful output about what actually
+# was included.
+case ${boards_origin} in
+"command line")
+	print_skipped=1
+	;;
+environment*)
+	print_skipped=1
+	;;
+*)
+	print_skipped=0
+	;;
+esac
+
+for board in $@; do
+	board_cfg="arch/mips/configs/generic/board-${board}.config"
+	if [ ! -f "${board_cfg}" ]; then
+		echo "WARNING: Board config '${board_cfg}' not found"
+		continue
+	fi
+
+	# For each line beginning with # require, cut out the field following
+	# it & search for that in the reference config file. If the requirement
+	# is not found then the subshell will exit with code 1, and we'll
+	# continue on to the next board.
+	grep -E '^# require ' "${board_cfg}" | \
+	    cut -d' ' -f 3- | \
+	    while read req; do
+		case ${req} in
+		*=y)
+			# If we require something =y then we check that a line
+			# containing it is present in the reference config.
+			grep -Eq "^${req}\$" "${ref_cfg}" && continue
+			;;
+		*=n)
+			# If we require something =n then we just invert that
+			# check, considering the requirement met if there isn't
+			# a line containing the value =y in the reference
+			# config.
+			grep -Eq "^${req/%=n/=y}\$" "${ref_cfg}" || continue
+			;;
+		*)
+			echo "WARNING: Unhandled requirement '${req}'"
+			;;
+		esac
+
+		[ ${print_skipped} -eq 1 ] && echo "Skipping ${board_cfg}"
+		exit 1
+	done || continue
+
+	# Merge this board config fragment into our final config file
+	./scripts/kconfig/merge_config.sh \
+		-m -O ${objtree} ${cfg} ${board_cfg} \
+		| grep -Ev '^(#|Using)'
+done