MIPS: Use Kconfig to select CPU_NO_EFFICIENT_FFS

Select CONFIG_CPU_NO_EFFICIENT_FFS via Kconfig when the kernel is
configured for a pre-MIPS32r1 CPU, rather than defining its equivalent
in asm/cpu-features.h based upon overrides of cpu_has_mips* macros.

The latter only works if a platform has an cpu-feature-overrides.h
header which defines cpu_has_mips* macros, which are not generally
needed. There are many cases where we know that the target ISA for a
kernel build is MIPS32r1 or later & thus includes the CLZ instruction,
without requiring any overrides from the platform. Using Kconfig allows
us to take those into account, and more naturally make a decision about
instruction support using information about the target ISA.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/21045/
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Zhaoxiu Zeng <zhaoxiu.zeng@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org

arch/mips/Kconfig

@@ -15,6 +15,7 @@ config MIPS
 	select ARCH_WANT_IPC_PARSE_VERSION
 	select BUILDTIME_EXTABLE_SORT
 	select CLONE_BACKWARDS
+	select CPU_NO_EFFICIENT_FFS if (TARGET_ISA_REV < 1)
 	select CPU_PM if CPU_IDLE
 	select DMA_DIRECT_OPS
 	select GENERIC_ATOMIC64 if !64BIT
@@ -2031,7 +2032,7 @@ config CPU_MIPS64
 	default y if CPU_MIPS64_R1 || CPU_MIPS64_R2 || CPU_MIPS64_R6
 
 #
-# These two indicate the revision of the architecture, either Release 1 or Release 2
+# These indicate the revision of the architecture
 #
 config CPU_MIPSR1
 	bool
@@ -2052,6 +2053,16 @@ config CPU_MIPSR6
 	select MIPS_CRC_SUPPORT
 	select MIPS_SPRAM
 
+config TARGET_ISA_REV
+	int
+	default 1 if CPU_MIPSR1
+	default 2 if CPU_MIPSR2
+	default 6 if CPU_MIPSR6
+	default 0
+	help
+	  Reflects the ISA revision being targeted by the kernel build. This
+	  is effectively the Kconfig equivalent of MIPS_ISA_REV.
+
 config EVA
 	bool
 

arch/mips/include/asm/cpu-features.h

@@ -253,16 +253,6 @@
 #endif
 #endif
 
-/* __builtin_constant_p(cpu_has_mips_r) && cpu_has_mips_r */
-#if !((defined(cpu_has_mips32r1) && cpu_has_mips32r1) || \
-	  (defined(cpu_has_mips32r2) && cpu_has_mips32r2) || \
-	  (defined(cpu_has_mips32r6) && cpu_has_mips32r6) || \
-	  (defined(cpu_has_mips64r1) && cpu_has_mips64r1) || \
-	  (defined(cpu_has_mips64r2) && cpu_has_mips64r2) || \
-	  (defined(cpu_has_mips64r6) && cpu_has_mips64r6))
-#define CPU_NO_EFFICIENT_FFS 1
-#endif
-
 #ifndef cpu_has_mips_1
 # define cpu_has_mips_1		(!cpu_has_mips_r6)
 #endif