Commit a256ae22 authored by Luo Jie's avatar Luo Jie Committed by Yury Norov
Browse files

bitfield: Add FIELD_MODIFY() helper 



Add a helper for replacing the contents of bitfield in memory
with the specified value.

Even though a helper xxx_replace_bits() is available, it is not
well documented, and only reports errors at the run time, which
will not be helpful to catch possible overflow errors due to
incorrect parameter types used.

FIELD_MODIFY(REG_FIELD_C, &reg, c) is the wrapper to the code below.

	reg &= ~REG_FIELD_C;
	reg |= FIELD_PREP(REG_FIELD_C, c);

Yury: trim commit message, align backslashes.

Signed-off-by: default avatarLuo Jie <quic_luoj@quicinc.com>
Signed-off-by: default avatarYury Norov <yury.norov@gmail.com>
parent 89a44a80

include/linux/bitfield.h

+19 −2
Original line number Diff line number Diff line
@@ -8,6 +8,7 @@ 
#define _LINUX_BITFIELD_H



#include <linux/build_bug.h>

#include <linux/typecheck.h>

#include <asm/byteorder.h>



/*
@@ -38,8 +39,7 @@ 
 *	  FIELD_PREP(REG_FIELD_D, 0x40);

 *

 * Modify:

 *  reg &= ~REG_FIELD_C;

 *  reg |= FIELD_PREP(REG_FIELD_C, c);

 *  FIELD_MODIFY(REG_FIELD_C, &reg, c);

 */



#define __bf_shf(x) (__builtin_ffsll(x) - 1)
@@ -156,6 +156,23 @@ 
		(typeof(_mask))(((_reg) & (_mask)) >> __bf_shf(_mask));	\

	})



/**

 * FIELD_MODIFY() - modify a bitfield element

 * @_mask: shifted mask defining the field's length and position

 * @_reg_p: pointer to the memory that should be updated

 * @_val: value to store in the bitfield

 *

 * FIELD_MODIFY() modifies the set of bits in @_reg_p specified by @_mask,

 * by replacing them with the bitfield value passed in as @_val.

 */

#define FIELD_MODIFY(_mask, _reg_p, _val)						\

	({										\

		typecheck_pointer(_reg_p);						\

		__BF_FIELD_CHECK(_mask, *(_reg_p), _val, "FIELD_MODIFY: ");		\

		*(_reg_p) &= ~(_mask);							\

		*(_reg_p) |= (((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask));	\

	})



extern void __compiletime_error("value doesn't fit into mask")

__field_overflow(void);

extern void __compiletime_error("bad bitfield mask")