59 lines
2.2 KiB
Diff
59 lines
2.2 KiB
Diff
From e2192de59e457aef8d1f055a452131f0b3e5d097 Mon Sep 17 00:00:00 2001
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From: Johannes Berg <johannes.berg@intel.com>
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Date: Wed, 18 Jan 2023 14:26:53 +0100
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Subject: [PATCH] bitfield: add FIELD_PREP_CONST()
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Neither FIELD_PREP() nor *_encode_bits() can be used
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in constant contexts (such as initializers), but we
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don't want to define shift constants for all masks
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just for use in initializers, and having checks that
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the values fit is also useful.
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Therefore, add FIELD_PREP_CONST() which is a smaller
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version of FIELD_PREP() that can only take constant
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arguments and has less friendly (but not less strict)
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error checks, and expands to a constant value.
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Signed-off-by: Johannes Berg <johannes.berg@intel.com>
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Link: https://lore.kernel.org/r/20230118142652.53f20593504b.Iaeea0aee77a6493d70e573b4aa55c91c00e01e4b@changeid
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Signed-off-by: Johannes Berg <johannes.berg@intel.com>
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---
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include/linux/bitfield.h | 26 ++++++++++++++++++++++++++
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1 file changed, 26 insertions(+)
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--- a/include/linux/bitfield.h
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+++ b/include/linux/bitfield.h
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@@ -115,6 +115,32 @@
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((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask); \
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})
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+#define __BF_CHECK_POW2(n) BUILD_BUG_ON_ZERO(((n) & ((n) - 1)) != 0)
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+
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+/**
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+ * FIELD_PREP_CONST() - prepare a constant bitfield element
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+ * @_mask: shifted mask defining the field's length and position
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+ * @_val: value to put in the field
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+ *
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+ * FIELD_PREP_CONST() masks and shifts up the value. The result should
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+ * be combined with other fields of the bitfield using logical OR.
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+ *
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+ * Unlike FIELD_PREP() this is a constant expression and can therefore
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+ * be used in initializers. Error checking is less comfortable for this
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+ * version, and non-constant masks cannot be used.
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+ */
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+#define FIELD_PREP_CONST(_mask, _val) \
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+ ( \
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+ /* mask must be non-zero */ \
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+ BUILD_BUG_ON_ZERO((_mask) == 0) + \
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+ /* check if value fits */ \
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+ BUILD_BUG_ON_ZERO(~((_mask) >> __bf_shf(_mask)) & (_val)) + \
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+ /* check if mask is contiguous */ \
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+ __BF_CHECK_POW2((_mask) + (1ULL << __bf_shf(_mask))) + \
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+ /* and create the value */ \
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+ (((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask)) \
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+ )
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+
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/**
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* FIELD_GET() - extract a bitfield element
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* @_mask: shifted mask defining the field's length and position
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