Subject: [PATCH v2 03/16] bitmap: Use FIELD_PREP() in expansion of FIELD_PREP_WM16()

From: [email-masked]
Date: Fri, 12 Dec 2025 19:37:08 +0000

From: David Laight <[email-masked]>

Instead of directly expanding __BF_FIELD_CHECK() (which really ought
not be used outside bitfield) and open-coding the generation of the
masked value, just call FIELD_PREP() and add an extra check for
the mask being at most 16 bits.
The extra check is added after calling FIELD_PREP() to get a sane
error message if 'mask' isn't constant.

Remove the leading _ from the formal parameter names.
Prefix the local variables with _wm16_ to hopefully make them
unique.

Signed-off-by: David Laight <[email-masked]>
---

Changes for v2:
- Update kerneldoc to match changed formal parameter names.
- Change local variables to not collide with those in FIELD_PREP().

Most of the examples are constants and get optimised away.

 include/linux/hw_bitfield.h | 21 ++++++++++-----------
 1 file changed, 10 insertions(+), 11 deletions(-)

diff --git a/include/linux/hw_bitfield.h b/include/linux/hw_bitfield.h
index df202e167ce4..0bd1040a5f93 100644
--- a/include/linux/hw_bitfield.h
+++ b/include/linux/hw_bitfield.h
@@ -12,8 +12,8 @@
 
 /**
  * FIELD_PREP_WM16() - prepare a bitfield element with a mask in the upper half
- * @_mask: shifted mask defining the field's length and position
- * @_val:  value to put in the field
+ * @mask: shifted mask defining the field's length and position
+ * @val:  value to put in the field
  *
  * FIELD_PREP_WM16() masks and shifts up the value, as well as bitwise ORs the
  * result with the mask shifted up by 16.
@@ -23,15 +23,14 @@
  * register, a bit in the lower half is only updated if the corresponding bit
  * in the upper half is high.
  */
-#define FIELD_PREP_WM16(_mask, _val)					     \
-	({								     \
-		typeof(_val) __val = _val;				     \
-		typeof(_mask) __mask = _mask;				     \
-		__BF_FIELD_CHECK(__mask, ((u16)0U), __val,		     \
-				 "HWORD_UPDATE: ");			     \
-		(((typeof(__mask))(__val) << __bf_shf(__mask)) & (__mask)) | \
-		((__mask) << 16);					     \
-	})
+#define FIELD_PREP_WM16(mask, val)				\
+({								\
+	__auto_type _wm16_mask = mask;				\
+	u32 _wm16_val = FIELD_PREP(_wm16_mask, val);		\
+	BUILD_BUG_ON_MSG(_wm16_mask > 0xffffu,			\
+			 "FIELD_PREP_WM16: mask too large");	\
+	_wm16_val | (_wm16_mask << 16);				\
+})
 
 /**
  * FIELD_PREP_WM16_CONST() - prepare a constant bitfield element with a mask in
-- 
2.39.5