powerpc/64: Add GENERIC_CPU support for little endian

Add GENERIC_CPU support for little-endian rather than using POWER8
specific selection for POWER9 and above.

Restrict GENERIC_CPU to POWER8 and above on little endian.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Duplicate GENERIC_CPU to avoid a kbuild warning about the prompt
      being redefined. Spell out that GENERIC means >= POWER4 for BE.]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/Makefile

@@ -146,8 +146,13 @@ CFLAGS-$(CONFIG_PPC32)	:= -ffixed-r2 $(MULTIPLEWORD)
 CFLAGS-$(CONFIG_PPC32)	+= $(call cc-option,-mno-readonly-in-sdata)
 
 ifeq ($(CONFIG_PPC_BOOK3S_64),y)
+ifeq ($(CONFIG_CPU_LITTLE_ENDIAN),y)
+CFLAGS-$(CONFIG_GENERIC_CPU) += -mcpu=power8
+CFLAGS-$(CONFIG_GENERIC_CPU) += $(call cc-option,-mtune=power8)
+else
 CFLAGS-$(CONFIG_GENERIC_CPU) += $(call cc-option,-mtune=power7,$(call cc-option,-mtune=power5))
 CFLAGS-$(CONFIG_GENERIC_CPU) += $(call cc-option,-mcpu=power5,-mcpu=power4)
+endif
 else
 CFLAGS-$(CONFIG_GENERIC_CPU) += -mcpu=powerpc64
 endif

arch/powerpc/platforms/Kconfig.cputype

@@ -87,7 +87,6 @@ endchoice
 choice
 	prompt "CPU selection"
 	depends on PPC64
-	default POWER8_CPU if CPU_LITTLE_ENDIAN
 	default GENERIC_CPU
 	help
 	  This will create a kernel which is optimised for a particular CPU.
@@ -96,9 +95,14 @@ choice
 	  If unsure, select Generic.
 
 config GENERIC_CPU
-	bool "Generic"
+	bool "Generic (POWER4 and above)"
 	depends on !CPU_LITTLE_ENDIAN
 
+config GENERIC_CPU
+	bool "Generic (POWER8 and above)"
+	depends on CPU_LITTLE_ENDIAN
+	select ARCH_HAS_FAST_MULTIPLIER
+
 config CELL_CPU
 	bool "Cell Broadband Engine"
 	depends on PPC_BOOK3S_64 && !CPU_LITTLE_ENDIAN