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From: Arnd Bergmann <arnd@kernel.org>
To: Russell King <linux@armlinux.org.uk>
Cc: Arnd Bergmann <arnd@arndb.de>,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com
Subject: [PATCH] ARM: delay: avoid clang -Wtautological-constant warning
Date: Tue, 23 Mar 2021 14:20:23 +0100	[thread overview]
Message-ID: <20210323132031.2858996-1-arnd@kernel.org> (raw)

From: Arnd Bergmann <arnd@arndb.de>

Passing an 8-bit constant into delay() triggers a warning when building
with 'make W=1' using clang:

drivers/clk/actions/owl-pll.c:182:2: error: result of comparison of constant 2000 with expression of type 'u8' (aka 'unsigned char') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
        udelay(pll_hw->delay);
        ^~~~~~~~~~~~~~~~~~~~~
arch/arm/include/asm/delay.h:84:9: note: expanded from macro 'udelay'
          ((n) > (MAX_UDELAY_MS * 1000) ? __bad_udelay() :              \
           ~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~
arch/arm/mach-omap2/wd_timer.c:89:3: error: result of comparison of constant 2000 with expression of type 'u8' (aka 'unsigned char') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
                udelay(oh->class->sysc->srst_udelay);
                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Shut up the warning by adding a cast to a 64-bit number. A cast to 'int'
would usually be sufficient, but would fail to cause a link-time error
for large 64-bit constants.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 arch/arm/include/asm/delay.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/delay.h b/arch/arm/include/asm/delay.h
index 4f80b72372b4..1bb6417a3a83 100644
--- a/arch/arm/include/asm/delay.h
+++ b/arch/arm/include/asm/delay.h
@@ -81,7 +81,7 @@ extern void __bad_udelay(void);
 
 #define udelay(n)							\
 	(__builtin_constant_p(n) ?					\
-	  ((n) > (MAX_UDELAY_MS * 1000) ? __bad_udelay() :		\
+	  ((u64)(n) > (MAX_UDELAY_MS * 1000) ? __bad_udelay() :		\
 			__const_udelay((n) * UDELAY_MULT)) :		\
 	  __udelay(n))
 
-- 
2.29.2


WARNING: multiple messages have this Message-ID (diff)
From: Arnd Bergmann <arnd@kernel.org>
To: Russell King <linux@armlinux.org.uk>
Cc: Arnd Bergmann <arnd@arndb.de>,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com
Subject: [PATCH] ARM: delay: avoid clang -Wtautological-constant warning
Date: Tue, 23 Mar 2021 14:20:23 +0100	[thread overview]
Message-ID: <20210323132031.2858996-1-arnd@kernel.org> (raw)

From: Arnd Bergmann <arnd@arndb.de>

Passing an 8-bit constant into delay() triggers a warning when building
with 'make W=1' using clang:

drivers/clk/actions/owl-pll.c:182:2: error: result of comparison of constant 2000 with expression of type 'u8' (aka 'unsigned char') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
        udelay(pll_hw->delay);
        ^~~~~~~~~~~~~~~~~~~~~
arch/arm/include/asm/delay.h:84:9: note: expanded from macro 'udelay'
          ((n) > (MAX_UDELAY_MS * 1000) ? __bad_udelay() :              \
           ~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~
arch/arm/mach-omap2/wd_timer.c:89:3: error: result of comparison of constant 2000 with expression of type 'u8' (aka 'unsigned char') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
                udelay(oh->class->sysc->srst_udelay);
                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Shut up the warning by adding a cast to a 64-bit number. A cast to 'int'
would usually be sufficient, but would fail to cause a link-time error
for large 64-bit constants.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 arch/arm/include/asm/delay.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/delay.h b/arch/arm/include/asm/delay.h
index 4f80b72372b4..1bb6417a3a83 100644
--- a/arch/arm/include/asm/delay.h
+++ b/arch/arm/include/asm/delay.h
@@ -81,7 +81,7 @@ extern void __bad_udelay(void);
 
 #define udelay(n)							\
 	(__builtin_constant_p(n) ?					\
-	  ((n) > (MAX_UDELAY_MS * 1000) ? __bad_udelay() :		\
+	  ((u64)(n) > (MAX_UDELAY_MS * 1000) ? __bad_udelay() :		\
 			__const_udelay((n) * UDELAY_MULT)) :		\
 	  __udelay(n))
 
-- 
2.29.2


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             reply	other threads:[~2021-03-23 13:21 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-23 13:20 Arnd Bergmann [this message]
2021-03-23 13:20 ` [PATCH] ARM: delay: avoid clang -Wtautological-constant warning Arnd Bergmann
2021-03-23 13:30 ` Russell King - ARM Linux admin
2021-03-23 13:30   ` Russell King - ARM Linux admin
2021-03-24 23:14 ` David Laight
2021-03-24 23:14   ` David Laight

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