From: David Laight <david.laight.linux@gmail.com>

field_prep() calls __FIELD_PREP() which really wants the parameters
copied to 'locals' - but this is done later in __field_prep().

Move the 'auto_type' lines to the outer function.
This only leaves the shift calculation and final expression inside
__field_prep(), move the shift calculation to a new define __BF_SHIFT()
and just inline the final expression into  field_prep().
Use a common #define for the shift expression.

Do the same for field_get().

Signed-off-by: David Laight <david.laight.linux@gmail.com>
---
 include/linux/bitfield.h | 42 ++++++++++++++++++----------------------
 1 file changed, 19 insertions(+), 23 deletions(-)

diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h
index 3800744281c7..c30120535680 100644
--- a/include/linux/bitfield.h
+++ b/include/linux/bitfield.h
@@ -251,23 +251,9 @@ __MAKE_OP(64)
 #undef __MAKE_OP
 #undef ____MAKE_OP
 
-#define __field_prep(mask, val)						\
-	({								\
-		__auto_type __mask = (mask);				\
-		typeof(__mask) __val = (val);				\
-		unsigned int __shift = BITS_PER_TYPE(__mask) <= 32 ?	\
-				       __ffs(__mask) : __ffs64(__mask);	\
-		(__val << __shift) & __mask;				\
-	})
-
-#define __field_get(mask, reg)						\
-	({								\
-		__auto_type __mask = (mask);				\
-		typeof(__mask) __reg =  (reg);				\
-		unsigned int __shift = BITS_PER_TYPE(__mask) <= 32 ?	\
-				       __ffs(__mask) : __ffs64(__mask);	\
-		(__reg & __mask) >> __shift;				\
-	})
+/* As __bf_shf() but for non-zero variables */
+#define __BF_SHIFT(mask) \
+	(BITS_PER_TYPE(mask) <= 32 ? __ffs(mask) : __ffs64(mask))
 
 /**
  * field_prep() - prepare a bitfield element
@@ -285,9 +271,14 @@ __MAKE_OP(64)
  * If you want to ensure that @mask is a compile-time constant, please use
  * FIELD_PREP() directly instead.
  */
-#define field_prep(mask, val)						\
-	(__builtin_constant_p(mask) ? __FIELD_PREP(mask, val, "field_prep: ") \
-				    : __field_prep(mask, val))
+#define field_prep(mask, val)					\
+({								\
+	__auto_type _mask = mask;				\
+	__auto_type _val = 1 ? (val) : _mask;			\
+	__builtin_constant_p(_mask) ?				\
+		__FIELD_PREP(_mask, _val, "field_prep: ") :	\
+		(_val << __BF_SHIFT(_mask)) & _mask;		\
+})
 
 /**
  * field_get() - extract a bitfield element
@@ -305,8 +296,13 @@ __MAKE_OP(64)
  * If you want to ensure that @mask is a compile-time constant, please use
  * FIELD_GET() directly instead.
  */
-#define field_get(mask, reg)						\
-	(__builtin_constant_p(mask) ? __FIELD_GET(mask, reg, "field_get: ") \
-				    : __field_get(mask, reg))
+#define field_get(mask, reg)					\
+({								\
+	__auto_type _mask = mask;				\
+	__auto_type _reg = reg;					\
+	__builtin_constant_p(_mask) ?				\
+		__FIELD_GET(_mask, _reg, "field_get: ") :	\
+		(_reg & _mask) >> __BF_SHIFT(_mask);		\
+})
 
 #endif
-- 
2.39.5