firmware: Restore support for built-in firmware

Commit 5620a0d1aac ("firmware: delete in-kernel firmware") removed the
entire firmware directory.  Unfortunately it thereby also removed the
support for built-in firmware.

This restores the ability to build firmware directly into the kernel by
pruning the original Makefile to the necessary minimum.  The default for
EXTRA_FIRMWARE_DIR is now the standard directory /lib/firmware/.

Fixes: 5620a0d1aac ("firmware: delete in-kernel firmware")
Signed-off-by: Markus Trippelsdorf <markus@trippelsdorf.de>
Acked-by: Greg K-H <gregkh@linuxfoundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Makefile

@@ -562,7 +562,7 @@ scripts: scripts_basic include/config/auto.conf include/config/tristate.conf \
 
 # Objects we will link into vmlinux / subdirs we need to visit
 init-y		:= init/
-drivers-y	:= drivers/ sound/
+drivers-y	:= drivers/ sound/ firmware/
 net-y		:= net/
 libs-y		:= lib/
 core-y		:= usr/

drivers/base/Kconfig

@@ -140,13 +140,10 @@ config EXTRA_FIRMWARE
 config EXTRA_FIRMWARE_DIR
 	string "Firmware blobs root directory"
 	depends on EXTRA_FIRMWARE != ""
-	default "firmware"
+	default "/lib/firmware"
 	help
 	  This option controls the directory in which the kernel build system
 	  looks for the firmware files listed in the EXTRA_FIRMWARE option.
-	  The default is firmware/ in the kernel source tree, but by changing
-	  this option you can point it elsewhere, such as /lib/firmware/ or
-	  some other directory containing the firmware files.
 
 config FW_LOADER_USER_HELPER
 	bool

firmware/.gitignore

@@ -0,0 +1,6 @@
+*.gen.S
+*.fw
+*.bin
+*.csp
+*.dsp
+ihex2fw

firmware/Makefile

@@ -0,0 +1,63 @@
+#
+# kbuild file for firmware/
+#
+
+# Create $(fwabs) from $(CONFIG_EXTRA_FIRMWARE_DIR) -- if it doesn't have a
+# leading /, it's relative to $(srctree).
+fwdir := $(subst $(quote),,$(CONFIG_EXTRA_FIRMWARE_DIR))
+fwabs := $(addprefix $(srctree)/,$(filter-out /%,$(fwdir)))$(filter /%,$(fwdir))
+
+fw-external-y := $(subst $(quote),,$(CONFIG_EXTRA_FIRMWARE))
+
+quiet_cmd_fwbin = MK_FW   $@
+      cmd_fwbin = FWNAME="$(patsubst firmware/%.gen.S,%,$@)";		     \
+		  FWSTR="$(subst /,_,$(subst .,_,$(subst -,_,$(patsubst	     \
+				firmware/%.gen.S,%,$@))))";		     \
+		  ASM_WORD=$(if $(CONFIG_64BIT),.quad,.long);		     \
+		  ASM_ALIGN=$(if $(CONFIG_64BIT),3,2);			     \
+		  PROGBITS=$(if $(CONFIG_ARM),%,@)progbits;		     \
+		  echo "/* Generated by firmware/Makefile */"		> $@;\
+		  echo "    .section .rodata"				>>$@;\
+		  echo "    .p2align $${ASM_ALIGN}"			>>$@;\
+		  echo "_fw_$${FWSTR}_bin:"				>>$@;\
+		  echo "    .incbin \"$(2)\""				>>$@;\
+		  echo "_fw_end:"					>>$@;\
+		  echo "   .section .rodata.str,\"aMS\",$${PROGBITS},1"	>>$@;\
+		  echo "    .p2align $${ASM_ALIGN}"			>>$@;\
+		  echo "_fw_$${FWSTR}_name:"				>>$@;\
+		  echo "    .string \"$$FWNAME\""			>>$@;\
+		  echo "    .section .builtin_fw,\"a\",$${PROGBITS}"	>>$@;\
+		  echo "    .p2align $${ASM_ALIGN}"			>>$@;\
+		  echo "    $${ASM_WORD} _fw_$${FWSTR}_name"		>>$@;\
+		  echo "    $${ASM_WORD} _fw_$${FWSTR}_bin"		>>$@;\
+		  echo "    $${ASM_WORD} _fw_end - _fw_$${FWSTR}_bin"	>>$@;
+
+# One of these files will change, or come into existence, whenever
+# the configuration changes between 32-bit and 64-bit. The .S files
+# need to change when that happens.
+wordsize_deps := $(wildcard include/config/64bit.h include/config/32bit.h \
+		include/config/ppc32.h include/config/ppc64.h \
+		include/config/superh32.h include/config/superh64.h \
+		include/config/x86_32.h include/config/x86_64.h \
+		firmware/Makefile)
+
+$(patsubst %,$(obj)/%.gen.S, $(fw-external-y)): %: $(wordsize_deps) \
+		include/config/extra/firmware/dir.h
+	$(call cmd,fwbin,$(fwabs)/$(patsubst $(obj)/%.gen.S,%,$@))
+
+# The .o files depend on the binaries directly; the .S files don't.
+$(patsubst %,$(obj)/%.gen.o, $(fw-external-y)): $(obj)/%.gen.o: $(fwdir)/%
+
+obj-y				 += $(patsubst %,%.gen.o, $(fw-external-y))
+
+ifeq ($(KBUILD_SRC),)
+# Makefile.build only creates subdirectories for O= builds, but external
+# firmware might live outside the kernel source tree
+_dummy := $(foreach d,$(addprefix $(obj)/,$(dir $(fw-external-y))), $(shell [ -d $(d) ] || mkdir -p $(d)))
+endif
+
+targets := $(patsubst $(obj)/%,%, \
+                                $(shell find $(obj) -name \*.gen.S 2>/dev/null))
+# Without this, built-in.o won't be created when it's empty, and the
+# final vmlinux link will fail.
+obj- := dummy