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generic: 6.1: backport FIELD_PREP_CONST patch

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Backport FIELD_PREP_CONST patch needed for at803x backport patches to
correctly compile and work.

This MACRO is needed to treat values derived from FIELD_PREP usage as
const to be used by switch case or other needed usage.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
This commit is contained in:
Christian Marangi 2024-01-15 22:47:20 +01:00
parent 84a489b7cf
commit ef94541c07
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1 changed files with 58 additions and 0 deletions
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target/linux/generic/backport-6.1/200-v6.3-bitfield-add-FIELD_PREP_CONST.patch Normal file
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@ -0,0 +1,58 @@
From e2192de59e457aef8d1f055a452131f0b3e5d097 Mon Sep 17 00:00:00 2001
From: Johannes Berg <johannes.berg@intel.com>
Date: Wed, 18 Jan 2023 14:26:53 +0100
Subject: [PATCH] bitfield: add FIELD_PREP_CONST()
Neither FIELD_PREP() nor *_encode_bits() can be used
in constant contexts (such as initializers), but we
don't want to define shift constants for all masks
just for use in initializers, and having checks that
the values fit is also useful.
Therefore, add FIELD_PREP_CONST() which is a smaller
version of FIELD_PREP() that can only take constant
arguments and has less friendly (but not less strict)
error checks, and expands to a constant value.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Link: https://lore.kernel.org/r/20230118142652.53f20593504b.Iaeea0aee77a6493d70e573b4aa55c91c00e01e4b@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
include/linux/bitfield.h | 26 ++++++++++++++++++++++++++
1 file changed, 26 insertions(+)
--- a/include/linux/bitfield.h
+++ b/include/linux/bitfield.h
@@ -115,6 +115,32 @@
((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask); \
})
+#define __BF_CHECK_POW2(n) BUILD_BUG_ON_ZERO(((n) & ((n) - 1)) != 0)
+
+/**
+ * FIELD_PREP_CONST() - prepare a constant bitfield element
+ * @_mask: shifted mask defining the field's length and position
+ * @_val: value to put in the field
+ *
+ * FIELD_PREP_CONST() masks and shifts up the value. The result should
+ * be combined with other fields of the bitfield using logical OR.
+ *
+ * Unlike FIELD_PREP() this is a constant expression and can therefore
+ * be used in initializers. Error checking is less comfortable for this
+ * version, and non-constant masks cannot be used.
+ */
+#define FIELD_PREP_CONST(_mask, _val) \
+ ( \
+ /* mask must be non-zero */ \
+ BUILD_BUG_ON_ZERO((_mask) == 0) + \
+ /* check if value fits */ \
+ BUILD_BUG_ON_ZERO(~((_mask) >> __bf_shf(_mask)) & (_val)) + \
+ /* check if mask is contiguous */ \
+ __BF_CHECK_POW2((_mask) + (1ULL << __bf_shf(_mask))) + \
+ /* and create the value */ \
+ (((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask)) \
+ )
+
/**
* FIELD_GET() - extract a bitfield element
* @_mask: shifted mask defining the field's length and position