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[5.10.y-cip,02/19] bitfield: add FIELD_PREP_CONST()

Message ID 20240607140711.2497286-3-claudiu.beznea.uj@bp.renesas.com (mailing list archive)
State New
Headers show
Series Add suspend to RAM support for pin and IA55 IRQ controllers | expand

Commit Message

Claudiu Beznea June 7, 2024, 2:06 p.m. UTC 
From: Johannes Berg <johannes.berg@intel.com>

commit e2192de59e457aef8d1f055a452131f0b3e5d097 upstream.

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>
Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
---
 include/linux/bitfield.h | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)
diff mbox series

Patch

diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h
index 6093fa6db260..532442516bb4 100644
--- a/include/linux/bitfield.h
+++ b/include/linux/bitfield.h
@@ -112,6 +112,32 @@ 
 		((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