From: Johannes Berg <johannes@sipsolutions.net>
To: linux-wireless@vger.kernel.org
Cc: Felix Fietkau <nbd@nbd.name>, Jeff Johnson <jjohnson@kernel.org>,
ath11k@lists.infradead.org,
Johannes Berg <johannes.berg@intel.com>
Subject: [PATCH] bitfield: suppress "dubious: x & !y" sparse warning
Date: Fri, 23 Feb 2024 10:01:46 +0100 [thread overview]
Message-ID: <20240223100146.d243b6b1a9a1.I033828b1187c6bccf086e31400f7e933bb8373e7@changeid> (raw)
From: Johannes Berg <johannes.berg@intel.com>
There's a somewhat common pattern of using FIELD_PREP()
even for single bits, e.g.
cmd->info1 |= FIELD_PREP(HTT_SRNG_SETUP_CMD_INFO1_RING_FLAGS_MSI_SWAP,
!!(params.flags & HAL_SRNG_FLAGS_MSI_SWAP));
which might as well be written as
if (params.flags & HAL_SRNG_FLAGS_MSI_SWAP)
cmd->info1 |= HTT_SRNG_SETUP_CMD_INFO1_RING_FLAGS_MSI_SWAP;
(since info1 is fully initialized to start with), but in
a long chain of FIELD_PREP() this really seems fine.
However, it triggers a sparse warning, in the check in
the macro for whether a constant value fits into the mask,
as this contains a "& (_val)". In this case, this really
is always intentional, so just suppress the warning by
adding "0+" to the expression, indicating explicitly that
this is correct.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
include/linux/bitfield.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h
index ebfa12f69501..63928f173223 100644
--- a/include/linux/bitfield.h
+++ b/include/linux/bitfield.h
@@ -66,7 +66,8 @@
_pfx "mask is not constant"); \
BUILD_BUG_ON_MSG((_mask) == 0, _pfx "mask is zero"); \
BUILD_BUG_ON_MSG(__builtin_constant_p(_val) ? \
- ~((_mask) >> __bf_shf(_mask)) & (_val) : 0, \
+ ~((_mask) >> __bf_shf(_mask)) & \
+ (0 + (_val)) : 0, \
_pfx "value too large for the field"); \
BUILD_BUG_ON_MSG(__bf_cast_unsigned(_mask, _mask) > \
__bf_cast_unsigned(_reg, ~0ull), \
--
2.43.2
next reply other threads:[~2024-02-23 9:02 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-23 9:01 Johannes Berg [this message]
2024-02-28 11:54 ` [PATCH] bitfield: suppress "dubious: x & !y" sparse warning Kalle Valo
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