On 12/10/2018 20:45, Johannes Berg wrote:
From: Johannes Berg <johannes.berg@xxxxxxxxx>
John Garry requested to be able to use FIELD_PREP() and friends
in constant initializers, but we cannot completely switch all of
the current assertions to BUILD_BUG_ON_ZERO().
Thanks for this.
So instead of this, add __FIELD_PREP() which is suitable in such
contexts, and also add __{u,le,be}{16,32,64}encode_bits() like
the existing versions without underscores, but again suitable in
constant contexts.
Requested-by: John Garry <john.garry@xxxxxxxxxx>
Signed-off-by: Johannes Berg <johannes.berg@xxxxxxxxx>
---
include/linux/bitfield.h | 34 ++++++++++++++++++++++++++++++++++
1 file changed, 34 insertions(+)
diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h
index 3f1ef4450a7c..245dfb47d201 100644
--- a/include/linux/bitfield.h
+++ b/include/linux/bitfield.h
@@ -63,6 +63,14 @@
(1ULL << __bf_shf(_mask))); \
})
+#define __BF_CHECK_POW2(n) BUILD_BUG_ON_ZERO(((n) & ((n) - 1)) != 0)
+
+#define __BF_FIELD_CHECK_CONST(_mask, _reg, _val) \
+ (BUILD_BUG_ON_ZERO((_mask) == 0) + \
+ BUILD_BUG_ON_ZERO(~((_mask) >> __bf_shf(_mask)) & (_val)) + \
+ BUILD_BUG_ON_ZERO((_mask) > (typeof(_reg))~0ull) + \
+ __BF_CHECK_POW2((_mask) + (1ULL << __bf_shf(_mask))))
+
/**
* FIELD_FIT() - check if value fits in the field
* @_mask: shifted mask defining the field's length and position
@@ -90,6 +98,21 @@
((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask); \
})
+/**
+ * __FIELD_PREP() - prepare a constant bitfield element
My impression is that the name prefix - '__' - tells little about the
function. If you agree, how about even CFIELD_PREP() or
FIELD_PREP_CONST() or similar? I preper the latter, but becomes rather long.
+ * @_mask: shifted mask defining the field's length and position
+ * @_val: value to put in the field
+ *
+ * __FIELD_PREP() masks and shifts up the value. The result should
+ * be combined with other fields of the bitfield using local OR.
should this be 'logical OR', or indeed 'bitwise OR'?
+ *
+ * This version is suitable for use in a pure constant context, e.g.
+ * a constant initializer.
+ */
+#define __FIELD_PREP(_mask, _val) \
+ ((typeof(_mask))__BF_FIELD_CHECK_CONST(_mask, 0ULL, _val) + \
+ (((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask)))
+
/**
* FIELD_GET() - extract a bitfield element
* @_mask: shifted mask defining the field's length and position
@@ -150,4 +173,15 @@ __MAKE_OP(64)
#undef __MAKE_OP
#undef ____MAKE_OP
+#define __encode_bits(w, v, field) __FIELD_PREP((u##w)(field), v)
+#define __u16_encode_bits(v, field) __encode_bits(16, v, field)
+#define __le16_encode_bits(v, field) cpu_to_le16(__encode_bits(16, v, field))
+#define __be16_encode_bits(v, field) cpu_to_be16(__encode_bits(16, v, field))
+#define __u32_encode_bits(v, field) __encode_bits(32, v, field)
+#define __le32_encode_bits(v, field) cpu_to_le32(__encode_bits(32, v, field))
+#define __be32_encode_bits(v, field) cpu_to_be32(__encode_bits(32, v, field))
+#define __u64_encode_bits(v, field) __encode_bits(64, v, field)
+#define __le64_encode_bits(v, field) cpu_to_le64(__encode_bits(64, v, field))
+#define __be64_encode_bits(v, field) cpu_to_be64(__encode_bits(64, v, field))
+
#endif
Thanks again,
John
