hw_bitfield.h

 1/* SPDX-License-Identifier: GPL-2.0-or-later */
 2/*
 3 * Copyright (C) 2025, Collabora Ltd.
 4 */
 5
 6#ifndef _LINUX_HW_BITFIELD_H
 7#define _LINUX_HW_BITFIELD_H
 8
 9#include <linux/bitfield.h>
10#include <linux/build_bug.h>
11#include <linux/limits.h>
12
13/**
14 * FIELD_PREP_WM16() - prepare a bitfield element with a mask in the upper half
15 * @_mask: shifted mask defining the field's length and position
16 * @_val:  value to put in the field
17 *
18 * FIELD_PREP_WM16() masks and shifts up the value, as well as bitwise ORs the
19 * result with the mask shifted up by 16.
20 *
21 * This is useful for a common design of hardware registers where the upper
22 * 16-bit half of a 32-bit register is used as a write-enable mask. In such a
23 * register, a bit in the lower half is only updated if the corresponding bit
24 * in the upper half is high.
25 */
26#define FIELD_PREP_WM16(_mask, _val)					     \
27	({								     \
28		typeof(_val) __val = _val;				     \
29		typeof(_mask) __mask = _mask;				     \
30		__BF_FIELD_CHECK(__mask, ((u16)0U), __val,		     \
31				 "HWORD_UPDATE: ");			     \
32		(((typeof(__mask))(__val) << __bf_shf(__mask)) & (__mask)) | \
33		((__mask) << 16);					     \
34	})
35
36/**
37 * FIELD_PREP_WM16_CONST() - prepare a constant bitfield element with a mask in
38 *                           the upper half
39 * @_mask: shifted mask defining the field's length and position
40 * @_val:  value to put in the field
41 *
42 * FIELD_PREP_WM16_CONST() masks and shifts up the value, as well as bitwise ORs
43 * the result with the mask shifted up by 16.
44 *
45 * This is useful for a common design of hardware registers where the upper
46 * 16-bit half of a 32-bit register is used as a write-enable mask. In such a
47 * register, a bit in the lower half is only updated if the corresponding bit
48 * in the upper half is high.
49 *
50 * Unlike FIELD_PREP_WM16(), this is a constant expression and can therefore
51 * be used in initializers. Error checking is less comfortable for this
52 * version.
53 */
54#define FIELD_PREP_WM16_CONST(_mask, _val)				 \
55	(								 \
56		FIELD_PREP_CONST(_mask, _val) |				 \
57		(BUILD_BUG_ON_ZERO(const_true((u64)(_mask) > U16_MAX)) + \
58		 ((_mask) << 16))					 \
59	)
60
61
62#endif /* _LINUX_HW_BITFIELD_H */