openrisc: Add gcc machine instruction flag configuration

OpenRISC GCC supports flags to enable the backend to output instructions
if they are supported by a target processor.  This patch adds
configuration flags to enable configuring these flags to tune the kernel
for a particular CPU configuration.

In the future we could also enable all of these flags by default and
provide instruction emulation in the kernel to make these choices easier
for users but this is what we provide for now.

Signed-off-by: Stafford Horne <[email protected]>

Author: stffrdhrn

arch/openrisc/Kconfig

@@ -114,6 +114,59 @@ config OPENRISC_HAVE_INST_DIV
 	default y
 	help
 	  Select this if your implementation has a hardware divide instruction
+
+config OPENRISC_HAVE_INST_CMOV
+	bool "Have instruction l.cmov for conditional move"
+	default n
+	help
+	  This config enables gcc to generate l.cmov instructions when compiling
+	  the kernel which in general will improve performance and reduce the
+	  binary size.
+
+	  Select this if your implementation has support for the Class II
+	  l.cmov conistional move instruction.
+
+	  Say N if you are unsure.
+
+config OPENRISC_HAVE_INST_ROR
+	bool "Have instruction l.ror for rotate right"
+	default n
+	help
+	  This config enables gcc to generate l.ror instructions when compiling
+	  the kernel which in general will improve performance and reduce the
+	  binary size.
+
+	  Select this if your implementation has support for the Class II
+	  l.ror rotate right instruction.
+
+	  Say N if you are unsure.
+
+config OPENRISC_HAVE_INST_RORI
+	bool "Have instruction l.rori for rotate right with immediate"
+	default n
+	help
+	  This config enables gcc to generate l.rori instructions when compiling
+	  the kernel which in general will improve performance and reduce the
+	  binary size.
+
+	  Select this if your implementation has support for the Class II
+	  l.rori rotate right with immediate instruction.
+
+	  Say N if you are unsure.
+
+config OPENRISC_HAVE_INST_SEXT
+	bool "Have instructions l.ext* for sign extension"
+	default n
+	help
+	  This config enables gcc to generate l.ext* instructions when compiling
+	  the kernel which in general will improve performance and reduce the
+	  binary size.
+
+	  Select this if your implementation has support for the Class II
+	  l.exths, l.extbs, l.exthz and l.extbz size extend instructions.
+
+	  Say N if you are unsure.
+
 endmenu
 
 config NR_CPUS

arch/openrisc/Makefile

@@ -21,6 +21,7 @@ OBJCOPYFLAGS    := -O binary -R .note -R .comment -S
 LIBGCC 		:= $(shell $(CC) $(KBUILD_CFLAGS) -print-libgcc-file-name)
 
 KBUILD_CFLAGS	+= -pipe -ffixed-r10 -D__linux__
+KBUILD_CFLAGS	+= -msfimm -mshftimm
 
 all: vmlinux.bin
 
@@ -38,6 +39,22 @@ else
 	KBUILD_CFLAGS += $(call cc-option,-msoft-div)
 endif
 
+ifeq ($(CONFIG_OPENRISC_HAVE_INST_CMOV),y)
+	KBUILD_CFLAGS += $(call cc-option,-mcmov)
+endif
+
+ifeq ($(CONFIG_OPENRISC_HAVE_INST_ROR),y)
+	KBUILD_CFLAGS += $(call cc-option,-mror)
+endif
+
+ifeq ($(CONFIG_OPENRISC_HAVE_INST_RORI),y)
+	KBUILD_CFLAGS += $(call cc-option,-mrori)
+endif
+
+ifeq ($(CONFIG_OPENRISC_HAVE_INST_SEXT),y)
+	KBUILD_CFLAGS += $(call cc-option,-msext)
+endif
+
 head-y 		:= arch/openrisc/kernel/head.o
 
 libs-y		+= $(LIBGCC)