bitfield: Add less-checking __FIELD_{GET,PREP}()

The BUILD_BUG_ON_MSG() check against "~0ull" works only with "unsigned
(long) long" _mask types.  For constant masks, that condition is usually
met, as GENMASK() yields an UL value.  The few places where the
constant mask is stored in an intermediate variable were fixed by
changing the variable type to u64.

However, for non-constant masks, smaller unsigned types should be valid,
too, but currently lead to "result of comparison of constant
18446744073709551615 with expression of type ... is always
false"-warnings with clang and W=1.

Hence refactor the __BF_FIELD_CHECK() helper, and factor out
__FIELD_{GET,PREP}().  The later lack the single problematic check, but
are otherwise identical to FIELD_{GET,PREP}(), and are intended to be
used in the fully non-const variants later.

Signed-off-by: Geert Uytterhoeven <[email protected]>
Signed-off-by: Yury Norov (NVIDIA) <[email protected]>
[Linux commit: 2a6c045640c38a407a39cd40c3c4d8dd2fd89aa8]
Signed-off-by: Mikhail Kshevetskiy <[email protected]>
Reviewed-by: David Lechner <[email protected]>
Reviewed-by: Simon Glass <[email protected]>
Signed-off-by: Scott Wood <[email protected]>
Acked-by: Gerald Van Baren <[email protected]>
Reviewed-by: Andre Przywara <[email protected]>
Signed-off-by: Masahiro Yamada <[email protected]>

1 files changed, 28 insertions, 8 deletions

diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h
index 63928f17322..ef81901bc41 100644
--- a/include/linux/bitfield.h
+++ b/include/linux/bitfield.h
@@ -60,7 +60,7 @@
 
 #define __bf_cast_unsigned(type, x)	((__unsigned_scalar_typeof(type))(x))
 
-#define __BF_FIELD_CHECK(_mask, _reg, _val, _pfx)			\
+#define __BF_FIELD_CHECK_MASK(_mask, _val, _pfx)			\
 	({								\
 		BUILD_BUG_ON_MSG(!__builtin_constant_p(_mask),		\
 				 _pfx "mask is not constant");		\
@@ -69,13 +69,33 @@
 				 ~((_mask) >> __bf_shf(_mask)) &	\
 					(0 + (_val)) : 0,		\
 				 _pfx "value too large for the field"); \
-		BUILD_BUG_ON_MSG(__bf_cast_unsigned(_mask, _mask) >	\
-				 __bf_cast_unsigned(_reg, ~0ull),	\
-				 _pfx "type of reg too small for mask"); \
 		__BUILD_BUG_ON_NOT_POWER_OF_2((_mask) +			\
 					      (1ULL << __bf_shf(_mask))); \
 	})
 
+#define __BF_FIELD_CHECK_REG(mask, reg, pfx)				\
+	BUILD_BUG_ON_MSG(__bf_cast_unsigned(mask, mask) >		\
+			 __bf_cast_unsigned(reg, ~0ull),		\
+			 pfx "type of reg too small for mask")
+
+#define __BF_FIELD_CHECK(mask, reg, val, pfx)				\
+	({								\
+		__BF_FIELD_CHECK_MASK(mask, val, pfx);			\
+		__BF_FIELD_CHECK_REG(mask, reg, pfx);			\
+	})
+
+#define __FIELD_PREP(mask, val, pfx)					\
+	({								\
+		__BF_FIELD_CHECK_MASK(mask, val, pfx);			\
+		((typeof(mask))(val) << __bf_shf(mask)) & (mask);	\
+	})
+
+#define __FIELD_GET(mask, reg, pfx)					\
+	({								\
+		__BF_FIELD_CHECK_MASK(mask, 0U, pfx);			\
+		(typeof(mask))(((reg) & (mask)) >> __bf_shf(mask));	\
+	})
+
 /**
  * FIELD_MAX() - produce the maximum value representable by a field
  * @_mask: shifted mask defining the field's length and position
@@ -112,8 +132,8 @@
  */
 #define FIELD_PREP(_mask, _val)						\
 	({								\
-		__BF_FIELD_CHECK(_mask, 0ULL, _val, "FIELD_PREP: ");	\
-		((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask);	\
+		__BF_FIELD_CHECK_REG(_mask, 0ULL, "FIELD_PREP: ");	\
+		__FIELD_PREP(_mask, _val, "FIELD_PREP: ");		\
 	})
 
 #define __BF_CHECK_POW2(n)	BUILD_BUG_ON_ZERO(((n) & ((n) - 1)) != 0)
@@ -152,8 +172,8 @@
  */
 #define FIELD_GET(_mask, _reg)						\
 	({								\
-		__BF_FIELD_CHECK(_mask, _reg, 0U, "FIELD_GET: ");	\
-		(typeof(_mask))(((_reg) & (_mask)) >> __bf_shf(_mask));	\
+		__BF_FIELD_CHECK_REG(_mask, _reg, "FIELD_GET: ");	\
+		__FIELD_GET(_mask, _reg, "FIELD_GET: ");		\
 	})
 
 extern void __compiletime_error("value doesn't fit into mask")