bitfield.h: add FIELD_MAX() and field_max()

Define FIELD_MAX(), which supplies the maximum value that can be
represented by a field value.  Define field_max() as well, to go
along with the lower-case forms of the field mask functions.

Signed-off-by: Alex Elder <elder@linaro.org>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h
index 4bbb5f1..48ea093 100644 (file)
--- a/include/linux/bitfield.h
+++ b/include/linux/bitfield.h
@@ -56,6 +56,19 @@
        })
 
 /**
+ * FIELD_MAX() - produce the maximum value representable by a field
+ * @_mask: shifted mask defining the field's length and position
+ *
+ * FIELD_MAX() returns the maximum value that can be held in the field
+ * specified by @_mask.
+ */
+#define FIELD_MAX(_mask)                                               \
+       ({                                                              \
+               __BF_FIELD_CHECK(_mask, 0ULL, 0ULL, "FIELD_MAX: ");     \
+               (typeof(_mask))((_mask) >> __bf_shf(_mask));            \
+       })
+
+/**
  * FIELD_FIT() - check if value fits in the field
  * @_mask: shifted mask defining the field's length and position
  * @_val:  value to test against the field
@@ -110,6 +123,7 @@ static __always_inline u64 field_mask(u64 field)
 {
        return field / field_multiplier(field);
 }
+#define field_max(field)       ((typeof(field))field_mask(field))
 #define ____MAKE_OP(type,base,to,from)                                 \
 static __always_inline __##type type##_encode_bits(base v, base field) \
 {                                                                      \