Hardware of various vendors, but very notably Rockchip, often uses
32-bit registers where the upper 16-bit half of the register is a
write-enable mask for the lower half.
Add hw_bitfield.h with two macros: FIELD_PREP_WM16, and
FIELD_PREP_WM16_CONST. The latter is a version that can be used in
initializers, like FIELD_PREP_CONST.
Import hw_bitfield.h from Linux commit 21368fcbb124 ("bitmap: introduce
hardware-specific bitfield operations"), first introduced in v6.18-rc1.
This contains two changes compared to the Linux version:
- include of linux/limit.h was dropped
- use of const_true() in FIELD_PREP_WM16_CONST() was dropped
Signed-off-by: Jonas Karlman <[email protected]>
---
v2: New patch
---
include/linux/hw_bitfield.h | 61 +++++++++++++++++++++++++++++++++++++
1 file changed, 61 insertions(+)
create mode 100644 include/linux/hw_bitfield.h
diff --git a/include/linux/hw_bitfield.h b/include/linux/hw_bitfield.h
new file mode 100644
index 000000000000..6e74d902ed33
--- /dev/null
+++ b/include/linux/hw_bitfield.h
@@ -0,0 +1,61 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2025, Collabora Ltd.
+ */
+
+#ifndef _LINUX_HW_BITFIELD_H
+#define _LINUX_HW_BITFIELD_H
+
+#include <linux/bitfield.h>
+#include <linux/build_bug.h>
+
+/**
+ * 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
+ *
+ * FIELD_PREP_WM16() masks and shifts up the value, as well as bitwise ORs the
+ * result with the mask shifted up by 16.
+ *
+ * This is useful for a common design of hardware registers where the upper
+ * 16-bit half of a 32-bit register is used as a write-enable mask. In such a
+ * 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); \
+ })
+
+/**
+ * FIELD_PREP_WM16_CONST() - prepare a constant 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
+ *
+ * FIELD_PREP_WM16_CONST() masks and shifts up the value, as well as bitwise
ORs
+ * the result with the mask shifted up by 16.
+ *
+ * This is useful for a common design of hardware registers where the upper
+ * 16-bit half of a 32-bit register is used as a write-enable mask. In such a
+ * register, a bit in the lower half is only updated if the corresponding bit
+ * in the upper half is high.
+ *
+ * Unlike FIELD_PREP_WM16(), this is a constant expression and can therefore
+ * be used in initializers. Error checking is less comfortable for this
+ * version.
+ */
+#define FIELD_PREP_WM16_CONST(_mask, _val) \
+ ( \
+ FIELD_PREP_CONST(_mask, _val) | \
+ (BUILD_BUG_ON_ZERO((u64)(_mask) > U16_MAX) + \
+ ((_mask) << 16)) \
+ )
+
+
+#endif /* _LINUX_HW_BITFIELD_H */
--
2.54.0
