powerpc/64: Set default CPU in Kconfig

Since commit 0069f3d1 ("powerpc/64e: Tie PPC_BOOK3E_64 to
PPC_E500MC"), the only possible BOOK3E/64 are E500, so no need of a
default CPU over the E5500.

When the user selects book3e, they must have an e500 compatible
compiler, and it won't work anymore with the default -mcpu=power64, see
commit d6b551b8 ("powerpc/64e: Fix build failure with GCC
12 (unrecognized opcode: `wrteei')").

For book3s/64, replace GENERIC_CPU by POWERPC64_CPU to match the PPC32
POWERPC_CPU, and set a default mpcu value in Kconfig directly.

When a user selects a particular CPU, they must ensure the compiler has
the requested capability. Therefore, remove hidden fallback, instead
offer user the possibility to say they want to use the toolchain
default.

Fixes: d6b551b8 ("powerpc/64e: Fix build failure with GCC 12 (unrecognized opcode: `wrteei')")
Reported-by: Pali Rohár <pali@kernel.org>
Tested-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/76c11197b058193dcb8e8b26adffba09cfbdab11.1674632329.git.christophe.leroy@csgroup.eu

arch/powerpc/Makefile

@@ -146,19 +146,6 @@ CFLAGS-$(CONFIG_PPC32)	+= $(call cc-option, $(MULTIPLEWORD))
 
 CFLAGS-$(CONFIG_PPC32)	+= $(call cc-option,-mno-readonly-in-sdata)
 
-ifdef CONFIG_PPC_BOOK3S_64
-ifdef CONFIG_CPU_LITTLE_ENDIAN
-CFLAGS-$(CONFIG_GENERIC_CPU) += -mcpu=power8
-else
-CFLAGS-$(CONFIG_GENERIC_CPU) += -mcpu=power4
-endif
-CFLAGS-$(CONFIG_GENERIC_CPU) += $(call cc-option,-mtune=power10,	\
-				  $(call cc-option,-mtune=power9,	\
-				  $(call cc-option,-mtune=power8)))
-else ifdef CONFIG_PPC_BOOK3E_64
-CFLAGS-$(CONFIG_GENERIC_CPU) += -mcpu=powerpc64
-endif
-
 ifdef CONFIG_FUNCTION_TRACER
 CC_FLAGS_FTRACE := -pg
 ifdef CONFIG_MPROFILE_KERNEL
@@ -166,11 +153,12 @@ CC_FLAGS_FTRACE += -mprofile-kernel
 endif
 endif
 
-CFLAGS-$(CONFIG_TARGET_CPU_BOOL) += $(call cc-option,-mcpu=$(CONFIG_TARGET_CPU))
-AFLAGS-$(CONFIG_TARGET_CPU_BOOL) += $(call cc-option,-mcpu=$(CONFIG_TARGET_CPU))
+CFLAGS-$(CONFIG_TARGET_CPU_BOOL) += -mcpu=$(CONFIG_TARGET_CPU)
+AFLAGS-$(CONFIG_TARGET_CPU_BOOL) += -mcpu=$(CONFIG_TARGET_CPU)
 
-CFLAGS-$(CONFIG_E5500_CPU) += $(call cc-option,-mcpu=e500mc64,-mcpu=powerpc64)
-CFLAGS-$(CONFIG_E6500_CPU) += $(call cc-option,-mcpu=e6500,$(E5500_CPU))
+CFLAGS-$(CONFIG_POWERPC64_CPU) += $(call cc-option,-mtune=power10,	\
+				  $(call cc-option,-mtune=power9,	\
+				  $(call cc-option,-mtune=power8)))
 
 asinstr := $(call as-instr,lis 9$(comma)foo@high,-DHAVE_AS_ATHIGH=1)
 

arch/powerpc/platforms/Kconfig.cputype

@@ -118,19 +118,18 @@ endchoice
 
 choice
 	prompt "CPU selection"
-	default GENERIC_CPU
 	help
 	  This will create a kernel which is optimised for a particular CPU.
 	  The resulting kernel may not run on other CPUs, so use this with care.
 
 	  If unsure, select Generic.
 
-config GENERIC_CPU
+config POWERPC64_CPU
 	bool "Generic (POWER5 and PowerPC 970 and above)"
 	depends on PPC_BOOK3S_64 && !CPU_LITTLE_ENDIAN
 	select PPC_64S_HASH_MMU
 
-config GENERIC_CPU
+config POWERPC64_CPU
 	bool "Generic (POWER8 and above)"
 	depends on PPC_BOOK3S_64 && CPU_LITTLE_ENDIAN
 	select ARCH_HAS_FAST_MULTIPLIER
@@ -233,13 +232,12 @@ config E500MC_CPU
 
 config TOOLCHAIN_DEFAULT_CPU
 	bool "Rely on the toolchain's implicit default CPU"
-	depends on PPC32
 
 endchoice
 
 config TARGET_CPU_BOOL
 	bool
-	default !GENERIC_CPU && !TOOLCHAIN_DEFAULT_CPU
+	default !TOOLCHAIN_DEFAULT_CPU
 
 config TARGET_CPU
 	string
@@ -251,6 +249,10 @@ config TARGET_CPU
 	default "power8" if POWER8_CPU
 	default "power9" if POWER9_CPU
 	default "power10" if POWER10_CPU
+	default "e500mc64" if E5500_CPU
+	default "e6500" if E6500_CPU
+	default "power4" if POWERPC64_CPU && !CPU_LITTLE_ENDIAN
+	default "power8" if POWERPC64_CPU && CPU_LITTLE_ENDIAN
 	default "405" if 405_CPU
 	default "440" if 440_CPU
 	default "464" if 464_CPU