MIPS: Loongson-3: Improve -march option and move it to Platform

If GCC >= 4.9 and Binutils >=2.25, we use -march=loongson3a, otherwise
we use -march=mips64r2, this can slightly improve performance. Besides,
arch/mips/loongson64/Platform is a better location rather than arch/
mips/Makefile.

Signed-off-by: Huacai Chen <chenhc@lemote.com>
Cc: Aurelien Jarno <aurelien@aurel32.net>
Cc: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: Fuxin Zhang <zhangfx@lemote.com>
Cc: Zhangjin Wu <wuzhangjin@gmail.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/12161/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/Makefile

@@ -166,16 +166,6 @@ cflags-$(CONFIG_CPU_CAVIUM_OCTEON) += -Wa,-march=octeon
 endif
 cflags-$(CONFIG_CAVIUM_CN63XXP1) += -Wa,-mfix-cn63xxp1
 cflags-$(CONFIG_CPU_BMIPS)	+= -march=mips32 -Wa,-mips32 -Wa,--trap
-#
-# binutils from v2.25 on and gcc starting from v4.9.0 treat -march=loongson3a
-# as MIPS64 R1; older versions as just R1.  This leaves the possibility open
-# that GCC might generate R2 code for -march=loongson3a which then is rejected
-# by GAS.  The cc-option can't probe for this behaviour so -march=loongson3a
-# can't easily be used safely within the kbuild framework.
-#
-cflags-$(CONFIG_CPU_LOONGSON3)  +=					\
-	$(call cc-option,-march=mips64r2,-mips64r2 -U_MIPS_ISA -D_MIPS_ISA=_MIPS_ISA_MIPS64) \
-	-Wa,-mips64r2 -Wa,--trap
 
 cflags-$(CONFIG_CPU_R4000_WORKAROUNDS)	+= $(call cc-option,-mfix-r4000,)
 cflags-$(CONFIG_CPU_R4400_WORKAROUNDS)	+= $(call cc-option,-mfix-r4400,)

arch/mips/loongson64/Platform

@@ -22,6 +22,27 @@ ifdef CONFIG_CPU_LOONGSON2F_WORKAROUNDS
   endif
 endif
 
+cflags-$(CONFIG_CPU_LOONGSON3)	+= -Wa,--trap
+#
+# binutils from v2.25 on and gcc starting from v4.9.0 treat -march=loongson3a
+# as MIPS64 R2; older versions as just R1.  This leaves the possibility open
+# that GCC might generate R2 code for -march=loongson3a which then is rejected
+# by GAS.  The cc-option can't probe for this behaviour so -march=loongson3a
+# can't easily be used safely within the kbuild framework.
+#
+ifeq ($(call cc-ifversion, -ge, 0409, y), y)
+  ifeq ($(call ld-ifversion, -ge, 22500000, y), y)
+    cflags-$(CONFIG_CPU_LOONGSON3)  += \
+      $(call cc-option,-march=loongson3a -U_MIPS_ISA -D_MIPS_ISA=_MIPS_ISA_MIPS64)
+  else
+    cflags-$(CONFIG_CPU_LOONGSON3)  += \
+      $(call cc-option,-march=mips64r2,-mips64r2 -U_MIPS_ISA -D_MIPS_ISA=_MIPS_ISA_MIPS64)
+  endif
+else
+    cflags-$(CONFIG_CPU_LOONGSON3)  += \
+      $(call cc-option,-march=mips64r2,-mips64r2 -U_MIPS_ISA -D_MIPS_ISA=_MIPS_ISA_MIPS64)
+endif
+
 #
 # Loongson Machines' Support
 #