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

david.laight.linux
2025-12-12T19:38:18Z

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

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 <david.laight.linux@gmail.com>
---

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