linux-kernel - [PATCH v2] arm64/prefetch: fix a -Wtype-limits warning

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Date:   Fri,  2 Aug 2019 20:33:58 -0400
From:   Qian Cai <cai@....pw>
To:     will@...nel.org, catalin.marinas@....com
Cc:     rrichter@...ium.com, robin.murphy@....com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Qian Cai <cai@....pw>
Subject: [PATCH v2] arm64/prefetch: fix a -Wtype-limits warning

The commit d5370f754875 ("arm64: prefetch: add alternative pattern for
CPUs without a prefetcher") introduced MIDR_IS_CPU_MODEL_RANGE() to be
used in has_no_hw_prefetch() with rv_min=0 which generates a compilation
warning from GCC,

In file included from ./arch/arm64/include/asm/cache.h:8,
                from ./include/linux/cache.h:6,
                from ./include/linux/printk.h:9,
                from ./include/linux/kernel.h:15,
                from ./include/linux/cpumask.h:10,
                from arch/arm64/kernel/cpufeature.c:11:
arch/arm64/kernel/cpufeature.c: In function 'has_no_hw_prefetch':
./arch/arm64/include/asm/cputype.h:59:26: warning: comparison of
unsigned expression >= 0 is always true [-Wtype-limits]
 _model == (model) && rv >= (rv_min) && rv <= (rv_max);  \
                         ^~
arch/arm64/kernel/cpufeature.c:889:9: note: in expansion of macro
'MIDR_IS_CPU_MODEL_RANGE'
 return MIDR_IS_CPU_MODEL_RANGE(midr, MIDR_THUNDERX,
        ^~~~~~~~~~~~~~~~~~~~~~~

Fix it by making "rv" a "s32".

Signed-off-by: Qian Cai <cai@....pw>
---

v2: Use "s32" for "rv", so "variant 0/revision 0" can be covered.

 arch/arm64/include/asm/cputype.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/cputype.h b/arch/arm64/include/asm/cputype.h
index e7d46631cc42..d52fe8651c2d 100644
--- a/arch/arm64/include/asm/cputype.h
+++ b/arch/arm64/include/asm/cputype.h
@@ -54,7 +54,7 @@
 #define MIDR_IS_CPU_MODEL_RANGE(midr, model, rv_min, rv_max)		\
 ({									\
 	u32 _model = (midr) & MIDR_CPU_MODEL_MASK;			\
-	u32 rv = (midr) & (MIDR_REVISION_MASK | MIDR_VARIANT_MASK);	\
+	s32 rv = (midr) & (MIDR_REVISION_MASK | MIDR_VARIANT_MASK);	\
 									\
 	_model == (model) && rv >= (rv_min) && rv <= (rv_max);		\
  })
-- 
2.20.1 (Apple Git-117)