Commit 95b980d6 authored Jul 16, 2019 by Masahiro Yamada Committed by Linus Torvalds Jul 16, 2019

linux/bits.h: make BIT(), GENMASK(), and friends available in assembly

BIT(),  GENMASK(), etc. are useful to define register bits of hardware.
However, low-level code is often written in assembly, where they are
not available due to the hard-coded 1UL, 0UL.

In fact, in-kernel headers such as arch/arm64/include/asm/sysreg.h
use _BITUL() instead of BIT() so that the register bit macros are
available in assembly.

Using macros in include/uapi/linux/const.h have two reasons:

[1] For use in uapi headers
  We should use underscore-prefixed variants for user-space.

[2] For use in assembly code
  Since _BITUL() uses UL(1) instead of 1UL, it can be used as an
  alternative of BIT().

For [2], it is pretty easy to change BIT() etc. for use in assembly.

This allows to replace _BUTUL() in kernel-space headers with BIT().

Link: http://lkml.kernel.org/r/20190609153941.17249-1-yamada.masahiro@socionext.com


Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 65f50f25

include/linux/bits.h

+10 −7

Original line number	Diff line number	Diff line
		/* SPDX-License-Identifier: GPL-2.0 */
		#ifndef __LINUX_BITS_H
		#define __LINUX_BITS_H

		#include <linux/const.h>
		#include <asm/bitsperlong.h>

		#define BIT(nr) (1UL << (nr))
		#define BIT_ULL(nr) (1ULL << (nr))
		#define BIT_MASK(nr) (1UL << ((nr) % BITS_PER_LONG))
		#define BIT(nr) (UL(1) << (nr))
		#define BIT_ULL(nr) (ULL(1) << (nr))
		#define BIT_MASK(nr) (UL(1) << ((nr) % BITS_PER_LONG))
		#define BIT_WORD(nr) ((nr) / BITS_PER_LONG)
		#define BIT_ULL_MASK(nr) (1ULL << ((nr) % BITS_PER_LONG_LONG))
		#define BIT_ULL_MASK(nr) (ULL(1) << ((nr) % BITS_PER_LONG_LONG))
		#define BIT_ULL_WORD(nr) ((nr) / BITS_PER_LONG_LONG)
		#define BITS_PER_BYTE 8

		@@ -17,10 +19,11 @@
		* GENMASK_ULL(39, 21) gives us the 64bit vector 0x000000ffffe00000.
		*/
		#define GENMASK(h, l) \
		(((~0UL) - (1UL << (l)) + 1) & (~0UL >> (BITS_PER_LONG - 1 - (h))))
		(((~UL(0)) - (UL(1) << (l)) + 1) & \
		(~UL(0) >> (BITS_PER_LONG - 1 - (h))))

		#define GENMASK_ULL(h, l) \
		(((~0ULL) - (1ULL << (l)) + 1) & \
		(~0ULL >> (BITS_PER_LONG_LONG - 1 - (h))))
		(((~ULL(0)) - (ULL(1) << (l)) + 1) & \
		(~ULL(0) >> (BITS_PER_LONG_LONG - 1 - (h))))

		#endif /* __LINUX_BITS_H */

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