riscv: Avoid code duplication with generic bitops implementation

There's code duplication between the fallback implementation for bitops
__ffs/__fls/ffs/fls API and the generic C implementation in
include/asm-generic/bitops/. To avoid this duplication, this patch renames
the generic C implementation by adding a "generic_" prefix to them, then we
can use these generic APIs as fallback.

Suggested-by: Geert Uytterhoeven <[e-mail]>
Signed-off-by: Xiao Wang <[e-mail]>
Reviewed-by: Charlie Jenkins <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Palmer Dabbelt <[e-mail]>

arch/riscv/include/asm/bitops.h

···
 #include <asm-generic/bitops/fls.h>
 
 #else
+#define __HAVE_ARCH___FFS
+#define __HAVE_ARCH___FLS
+#define __HAVE_ARCH_FFS
+#define __HAVE_ARCH_FLS
+
+#include <asm-generic/bitops/__ffs.h>
+#include <asm-generic/bitops/__fls.h>
+#include <asm-generic/bitops/ffs.h>
+#include <asm-generic/bitops/fls.h>
+
 #include <asm/alternative-macros.h>
 #include <asm/hwcap.h>
 
···
 
 static __always_inline unsigned long variable__ffs(unsigned long word)
 {
-	int num;
-
 	asm_volatile_goto(ALTERNATIVE("j %l[legacy]", "nop", 0,
 				      RISCV_ISA_EXT_ZBB, 1)
 			  : : : : legacy);
···
 	return word;
 
 legacy:
-	num = 0;
-#if BITS_PER_LONG == 64
-	if ((word & 0xffffffff) == 0) {
-		num += 32;
-		word >>= 32;
-	}
-#endif
-	if ((word & 0xffff) == 0) {
-		num += 16;
-		word >>= 16;
-	}
-	if ((word & 0xff) == 0) {
-		num += 8;
-		word >>= 8;
-	}
-	if ((word & 0xf) == 0) {
-		num += 4;
-		word >>= 4;
-	}
-	if ((word & 0x3) == 0) {
-		num += 2;
-		word >>= 2;
-	}
-	if ((word & 0x1) == 0)
-		num += 1;
-	return num;
+	return generic___ffs(word);
 }
 
 /**
···
 
 static __always_inline unsigned long variable__fls(unsigned long word)
 {
-	int num;
-
 	asm_volatile_goto(ALTERNATIVE("j %l[legacy]", "nop", 0,
 				      RISCV_ISA_EXT_ZBB, 1)
 			  : : : : legacy);
···
 	return BITS_PER_LONG - 1 - word;
 
 legacy:
-	num = BITS_PER_LONG - 1;
-#if BITS_PER_LONG == 64
-	if (!(word & (~0ul << 32))) {
-		num -= 32;
-		word <<= 32;
-	}
-#endif
-	if (!(word & (~0ul << (BITS_PER_LONG - 16)))) {
-		num -= 16;
-		word <<= 16;
-	}
-	if (!(word & (~0ul << (BITS_PER_LONG - 8)))) {
-		num -= 8;
-		word <<= 8;
-	}
-	if (!(word & (~0ul << (BITS_PER_LONG - 4)))) {
-		num -= 4;
-		word <<= 4;
-	}
-	if (!(word & (~0ul << (BITS_PER_LONG - 2)))) {
-		num -= 2;
-		word <<= 2;
-	}
-	if (!(word & (~0ul << (BITS_PER_LONG - 1))))
-		num -= 1;
-	return num;
+	return generic___fls(word);
 }
 
 /**
···
 
 static __always_inline int variable_ffs(int x)
 {
-	int r;
-
-	if (!x)
-		return 0;
-
 	asm_volatile_goto(ALTERNATIVE("j %l[legacy]", "nop", 0,
 				      RISCV_ISA_EXT_ZBB, 1)
 			  : : : : legacy);
+
+	if (!x)
+		return 0;
 
 	asm volatile (".option push\n"
 		      ".option arch,+zbb\n"
 		      CTZW "%0, %1\n"
 		      ".option pop\n"
-		      : "=r" (r) : "r" (x) :);
+		      : "=r" (x) : "r" (x) :);
 
-	return r + 1;
+	return x + 1;
 
 legacy:
-	r = 1;
-	if (!(x & 0xffff)) {
-		x >>= 16;
-		r += 16;
-	}
-	if (!(x & 0xff)) {
-		x >>= 8;
-		r += 8;
-	}
-	if (!(x & 0xf)) {
-		x >>= 4;
-		r += 4;
-	}
-	if (!(x & 3)) {
-		x >>= 2;
-		r += 2;
-	}
-	if (!(x & 1)) {
-		x >>= 1;
-		r += 1;
-	}
-	return r;
+	return generic_ffs(x);
 }
 
 /**
···
 
 static __always_inline int variable_fls(unsigned int x)
 {
-	int r;
-
-	if (!x)
-		return 0;
-
 	asm_volatile_goto(ALTERNATIVE("j %l[legacy]", "nop", 0,
 				      RISCV_ISA_EXT_ZBB, 1)
 			  : : : : legacy);
+
+	if (!x)
+		return 0;
 
 	asm volatile (".option push\n"
 		      ".option arch,+zbb\n"
 		      CLZW "%0, %1\n"
 		      ".option pop\n"
-		      : "=r" (r) : "r" (x) :);
+		      : "=r" (x) : "r" (x) :);
 
-	return 32 - r;
+	return 32 - x;
 
 legacy:
-	r = 32;
-	if (!(x & 0xffff0000u)) {
-		x <<= 16;
-		r -= 16;
-	}
-	if (!(x & 0xff000000u)) {
-		x <<= 8;
-		r -= 8;
-	}
-	if (!(x & 0xf0000000u)) {
-		x <<= 4;
-		r -= 4;
-	}
-	if (!(x & 0xc0000000u)) {
-		x <<= 2;
-		r -= 2;
-	}
-	if (!(x & 0x80000000u)) {
-		x <<= 1;
-		r -= 1;
-	}
-	return r;
+	return generic_fls(x);
 }
 
 /**

include/asm-generic/bitops/__ffs.h

···
 #include <asm/types.h>
 
 /**
- * __ffs - find first bit in word.
+ * generic___ffs - find first bit in word.
  * @word: The word to search
  *
  * Undefined if no bit exists, so code should check against 0 first.
  */
-static __always_inline unsigned long __ffs(unsigned long word)
+static __always_inline unsigned long generic___ffs(unsigned long word)
 {
 	int num = 0;
 
···
 		num += 1;
 	return num;
 }
+
+#ifndef __HAVE_ARCH___FFS
+#define __ffs(word) generic___ffs(word)
+#endif
 
 #endif /* _ASM_GENERIC_BITOPS___FFS_H_ */

include/asm-generic/bitops/__fls.h

···
 #include <asm/types.h>
 
 /**
- * __fls - find last (most-significant) set bit in a long word
+ * generic___fls - find last (most-significant) set bit in a long word
  * @word: the word to search
  *
  * Undefined if no set bit exists, so code should check against 0 first.
  */
-static __always_inline unsigned long __fls(unsigned long word)
+static __always_inline unsigned long generic___fls(unsigned long word)
 {
 	int num = BITS_PER_LONG - 1;
 
···
 		num -= 1;
 	return num;
 }
+
+#ifndef __HAVE_ARCH___FLS
+#define __fls(word) generic___fls(word)
+#endif
 
 #endif /* _ASM_GENERIC_BITOPS___FLS_H_ */

include/asm-generic/bitops/ffs.h

···
 #define _ASM_GENERIC_BITOPS_FFS_H_
 
 /**
- * ffs - find first bit set
+ * generic_ffs - find first bit set
  * @x: the word to search
  *
  * This is defined the same way as
  * the libc and compiler builtin ffs routines, therefore
  * differs in spirit from ffz (man ffs).
  */
-static inline int ffs(int x)
+static inline int generic_ffs(int x)
 {
 	int r = 1;
 
···
 	}
 	return r;
 }
+
+#ifndef __HAVE_ARCH_FFS
+#define ffs(x) generic_ffs(x)
+#endif
 
 #endif /* _ASM_GENERIC_BITOPS_FFS_H_ */

include/asm-generic/bitops/fls.h

···
 #define _ASM_GENERIC_BITOPS_FLS_H_
 
 /**
- * fls - find last (most-significant) bit set
+ * generic_fls - find last (most-significant) bit set
  * @x: the word to search
  *
  * This is defined the same way as ffs.
  * Note fls(0) = 0, fls(1) = 1, fls(0x80000000) = 32.
  */
 
-static __always_inline int fls(unsigned int x)
+static __always_inline int generic_fls(unsigned int x)
 {
 	int r = 32;
 
···
 	}
 	return r;
 }
+
+#ifndef __HAVE_ARCH_FLS
+#define fls(x) generic_fls(x)
+#endif
 
 #endif /* _ASM_GENERIC_BITOPS_FLS_H_ */