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Message-Id: <1471540317-14823-1-git-send-email-jakub.kicinski@netronome.com>
Date: Thu, 18 Aug 2016 18:11:57 +0100
From: Jakub Kicinski <jakub.kicinski@...ronome.com>
To: torvalds@...ux-foundation.org
Cc: akpm@...ux-foundation.org, gregkh@...uxfoundation.org,
davem@...emloft.net, kvalo@...eaurora.org,
linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org,
dinan.gunawardena@...ronome.com,
Jakub Kicinski <jakub.kicinski@...ronome.com>
Subject: [RFC (v7)] add basic register-field manipulation macros
Hi!
This is what I came up with. Changes:
- drop the explicit type marking (u32/u64) - depend on the type
of the mask instead;
- only allow compilation time constant masks;
- barf at "type of register too small to ever match mask" on get;
- rename PUT -> PREP.
I did not put the new marcos in bitops.h (where GENMASK lives)
because of the dependency on bug.h. If I did there would be
a circular dependency like this:
bitops.h -> linux/bug.h -> asm-generic/bug.h -> kernel.h -> bitops.h
Which makes things really ugly. I tried to remove the kernel.h
include from bug.h by separating panic-related definitions into
a new header. There were still cycles coming from the notifier.h
which I had to include for panic notifier...
Reviewed-by: Dinan Gunawardena <dinan.gunawardena@...ronome.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
---
include/linux/bitfield.h | 93 ++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/bug.h | 3 ++
2 files changed, 96 insertions(+)
create mode 100644 include/linux/bitfield.h
diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h
new file mode 100644
index 000000000000..32ca8863e66d
--- /dev/null
+++ b/include/linux/bitfield.h
@@ -0,0 +1,93 @@
+/*
+ * Copyright (C) 2014 Felix Fietkau <nbd@....name>
+ * Copyright (C) 2004 - 2009 Ivo van Doorn <IvDoorn@...il.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2
+ * as published by the Free Software Foundation
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ */
+
+#ifndef _LINUX_BITFIELD_H
+#define _LINUX_BITFIELD_H
+
+#include <linux/bug.h>
+
+/*
+ * Bitfield access macros
+ *
+ * FIELD_{GET,PREP} macros take as first parameter shifted mask
+ * from which they extract the base mask and shift amount.
+ * Mask must be a compilation time constant.
+ *
+ * Example:
+ *
+ * #define REG_FIELD_A GENMASK(6, 0)
+ * #define REG_FIELD_B BIT(7)
+ * #define REG_FIELD_C GENMASK(15, 8)
+ * #define REG_FIELD_D GENMASK(31, 16)
+ *
+ * Get:
+ * a = FIELD_GET(REG_FIELD_A, reg);
+ * b = FIELD_GET(REG_FIELD_B, reg);
+ *
+ * Set:
+ * reg = FIELD_PREP(REG_FIELD_A, 1) |
+ * FIELD_PREP(REG_FIELD_B, 0) |
+ * FIELD_PREP(REG_FIELD_C, c) |
+ * FIELD_PREP(REG_FIELD_D, 0x40);
+ *
+ * Modify:
+ * reg &= ~REG_FIELD_C;
+ * reg |= FIELD_PREP(REG_FIELD_C, c);
+ */
+
+#define _bf_shf(x) (__builtin_ffsll(x) - 1)
+
+#define _BF_FIELD_CHECK(_mask, _reg, _val, _pfx) \
+ ({ \
+ BUILD_BUG_ON_MSG(!__builtin_constant_p(_mask), \
+ _pfx "mask is not constant"); \
+ BUILD_BUG_ON_MSG(!(_mask), _pfx "mask is zero"); \
+ BUILD_BUG_ON_MSG(__builtin_constant_p(_val) ? \
+ ~((_mask) >> _bf_shf(_mask)) & (_val) : 0, \
+ _pfx "value too large for the field"); \
+ BUILD_BUG_ON_MSG((_mask) > (typeof(_reg))~0ull, \
+ _pfx "type of reg too small for mask"); \
+ __BUILD_BUG_ON_NOT_POWER_OF_2((_mask) + \
+ (1ULL << _bf_shf(_mask))); \
+ })
+
+/**
+ * FIELD_PREP() - prepare a bitfield element
+ * @_mask: shifted mask defining the field's length and position
+ * @_val: value to put in the field
+ *
+ * FIELD_PREP() masks and shifts up the value. The result should
+ * be combined with other fields of the bitfield using logical OR.
+ */
+#define FIELD_PREP(_mask, _val) \
+ ({ \
+ _BF_FIELD_CHECK(_mask, 0ULL, _val, "FIELD_PREP: "); \
+ ((typeof(_mask))(_val) << _bf_shf(_mask)) & (_mask); \
+ })
+
+/**
+ * FIELD_GET() - extract a bitfield element
+ * @_mask: shifted mask defining the field's length and position
+ * @_reg: 32bit value of entire bitfield
+ *
+ * FIELD_GET() extracts the field specified by @_mask from the
+ * bitfield passed in as @_reg by masking and shifting it down.
+ */
+#define FIELD_GET(_mask, _reg) \
+ ({ \
+ _BF_FIELD_CHECK(_mask, _reg, 0U, "FIELD_GET: "); \
+ (typeof(_mask))(((_reg) & (_mask)) >> _bf_shf(_mask)); \
+ })
+
+#endif
diff --git a/include/linux/bug.h b/include/linux/bug.h
index e51b0709e78d..292d6a10b0c2 100644
--- a/include/linux/bug.h
+++ b/include/linux/bug.h
@@ -13,6 +13,7 @@ enum bug_trap_type {
struct pt_regs;
#ifdef __CHECKER__
+#define __BUILD_BUG_ON_NOT_POWER_OF_2(n) (0)
#define BUILD_BUG_ON_NOT_POWER_OF_2(n) (0)
#define BUILD_BUG_ON_ZERO(e) (0)
#define BUILD_BUG_ON_NULL(e) ((void*)0)
@@ -24,6 +25,8 @@ struct pt_regs;
#else /* __CHECKER__ */
/* Force a compilation error if a constant expression is not a power of 2 */
+#define __BUILD_BUG_ON_NOT_POWER_OF_2(n) \
+ BUILD_BUG_ON(((n) & ((n) - 1)) != 0)
#define BUILD_BUG_ON_NOT_POWER_OF_2(n) \
BUILD_BUG_ON((n) == 0 || (((n) & ((n) - 1)) != 0))
--
1.9.1
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