linux-kernel - [PATCH 08/22] bitops: introduce MANY

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Message-Id: <20220510154750.212913-9-yury.norov@gmail.com>
Date:   Tue, 10 May 2022 08:47:36 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        David Laight <David.Laight@...LAB.COM>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Joe Perches <joe@...ches.com>,
        Julia Lawall <Julia.Lawall@...ia.fr>,
        Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        Nicholas Piggin <npiggin@...il.com>,
        Nicolas Palix <nicolas.palix@...g.fr>,
        Peter Zijlstra <peterz@...radead.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Matti Vaittinen <Matti.Vaittinen@...rohmeurope.com>,
        linux-kernel@...r.kernel.org
Cc:     Yury Norov <yury.norov@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Chris Zankel <chris@...kel.net>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>,
        Max Filippov <jcmvbkbc@...il.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        linux-xtensa@...ux-xtensa.org
Subject: [PATCH 08/22] bitops: introduce MANY_BITS() macro

arch/xtensa/kernel/traps.c and include/linux/log2.h define very similar
functions with different behaviour. XTENSA defines IS_POW2(), and
log2.h defines is_power_of_2(). The difference is that IS_POW2()
considers 0 as power of 2, while is_power_of_2() - does not.

This discrepancy may confuse reader. From mathematical point of view,
0 is not a power of 2. So let's introduce macro MANY_BITS(), which
returns true if 2 or more bits are set in a number (which is what
XTENSA actually needs), and use it in is_power_of_2().

CC: Alexei Starovoitov <ast@...nel.org>
CC: Andrew Morton <akpm@...ux-foundation.org>
CC: Chris Zankel <chris@...kel.net>
CC: Christophe Leroy <christophe.leroy@...roup.eu>
CC: Eric W. Biederman <ebiederm@...ssion.com>
CC: Kumar Kartikeya Dwivedi <memxor@...il.com>
CC: Max Filippov <jcmvbkbc@...il.com>
CC: Toke Høiland-Jørgensen <toke@...hat.com>
CC: linux-xtensa@...ux-xtensa.org
CC: linux-kernel@...r.kernel.org
Signed-off-by: Yury Norov <yury.norov@...il.com>
---
 arch/xtensa/kernel/traps.c | 5 +----
 include/linux/bitops.h     | 3 +++
 include/linux/log2.h       | 2 +-
 3 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/xtensa/kernel/traps.c b/arch/xtensa/kernel/traps.c
index 138a86fbe9d7..040ec38bfce2 100644
--- a/arch/xtensa/kernel/traps.c
+++ b/arch/xtensa/kernel/traps.c
@@ -203,10 +203,7 @@ static void do_multihit(struct pt_regs *regs)
 
 #if XTENSA_FAKE_NMI
 
-#define IS_POW2(v) (((v) & ((v) - 1)) == 0)
-
-#if !(PROFILING_INTLEVEL == XCHAL_EXCM_LEVEL && \
-      IS_POW2(XTENSA_INTLEVEL_MASK(PROFILING_INTLEVEL)))
+#if (MANY_BITS(XTENSA_INTLEVEL_MASK(PROFILING_INTLEVEL)) || PROFILING_INTLEVEL != XCHAL_EXCM_LEVEL)
 #warning "Fake NMI is requested for PMM, but there are other IRQs at or above its level."
 #warning "Fake NMI will be used, but there will be a bugcheck if one of those IRQs fire."
 
diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index 7aaed501f768..96bc6a2552d6 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -21,6 +21,9 @@
 #define BITS_TO_U32(nr)		__KERNEL_DIV_ROUND_UP(nr, BITS_PER_TYPE(u32))
 #define BITS_TO_BYTES(nr)	__KERNEL_DIV_ROUND_UP(nr, BITS_PER_TYPE(char))
 
+/* Return: nonzero if 2 or more bits are set */
+#define MANY_BITS(n)		((n) & ((n) - 1))
+
 extern unsigned int __sw_hweight8(unsigned int w);
 extern unsigned int __sw_hweight16(unsigned int w);
 extern unsigned int __sw_hweight32(unsigned int w);
diff --git a/include/linux/log2.h b/include/linux/log2.h
index 9f30d087a128..335b9dbd302d 100644
--- a/include/linux/log2.h
+++ b/include/linux/log2.h
@@ -44,7 +44,7 @@ int __ilog2_u64(u64 n)
 static inline __attribute__((const))
 bool is_power_of_2(unsigned long n)
 {
-	return (n != 0 && ((n & (n - 1)) == 0));
+	return n != 0 && !MANY_BITS(n);
 }
 
 /**
-- 
2.32.0