linux-kernel - [PATCH -next] arm64: Optimize the comparison of unsigned expressions to avoid compiling error

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Date:   Tue, 21 Feb 2023 09:27:40 +0800
From:   Lin Yujun <linyujun809@...wei.com>
To:     <catalin.marinas@....com>, <will@...nel.org>, <broonie@...nel.org>,
        <kristina.martsenko@....com>, <mark.rutland@....com>,
        <james.morse@....com>, <maz@...nel.org>, <linyujun809@...wei.com>,
        <ardb@...nel.org>, <samitolvanen@...gle.com>,
        <andreyknvl@...il.com>, <masahiroy@...nel.org>,
        <joey.gouly@....com>, <anshuman.khandual@....com>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <wanghai38@...wei.com>
Subject: [PATCH -next] arm64: Optimize the comparison of unsigned expressions to avoid compiling error

while compile arch/arm64/include/asm/cpufeature.h with
-Werror=type-limits enabled, errors shown as below:

./arch/arm64/include/asm/cpufeature.h: In function 'system_supports_4kb_granule':
./arch/arm64/include/asm/cpufeature.h:653:14: error: comparison of unsigned expression >= 0 is always true [-Werror=type-limits]
  return (val >= ID_AA64MMFR0_TGRAN4_SUPPORTED_MIN) &&
              ^~
./arch/arm64/include/asm/cpufeature.h: In function 'system_supports_64kb_granule':
./arch/arm64/include/asm/cpufeature.h:666:14: error: comparison of unsigned expression >= 0 is always true [-Werror=type-limits]
  return (val >= ID_AA64MMFR0_TGRAN64_SUPPORTED_MIN) &&
              ^~
Modify the return judgment statement, use
"((val - min) < (val - max - 1))" to confirm that returns
true in “min <= val <= max” cases, false in other cases.

Fixes: 79d82cbcbb3d ("arm64/kexec: Test page size support with new TGRAN range values")
Signed-off-by: Lin Yujun <linyujun809@...wei.com>
---
 arch/arm64/include/asm/cpufeature.h | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 03d1c9d7af82..0a6bda025141 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -54,6 +54,9 @@ enum ftr_type {
 #define FTR_VISIBLE_IF_IS_ENABLED(config)		\
 	(IS_ENABLED(config) ? FTR_VISIBLE : FTR_HIDDEN)
 
+#define IN_RANGE_INCLUSIVE(val, min, max)		\
+	(((val) - (min)) < ((val) - (max) - 1))
+
 struct arm64_ftr_bits {
 	bool		sign;	/* Value is signed ? */
 	bool		visible;
@@ -693,8 +696,9 @@ static inline bool system_supports_4kb_granule(void)
 	val = cpuid_feature_extract_unsigned_field(mmfr0,
 						ID_AA64MMFR0_EL1_TGRAN4_SHIFT);
 
-	return (val >= ID_AA64MMFR0_EL1_TGRAN4_SUPPORTED_MIN) &&
-	       (val <= ID_AA64MMFR0_EL1_TGRAN4_SUPPORTED_MAX);
+	return IN_RANGE_INCLUSIVE(val,
+		ID_AA64MMFR0_EL1_TGRAN4_SUPPORTED_MIN,
+		ID_AA64MMFR0_EL1_TGRAN4_SUPPORTED_MAX);
 }
 
 static inline bool system_supports_64kb_granule(void)
@@ -706,8 +710,9 @@ static inline bool system_supports_64kb_granule(void)
 	val = cpuid_feature_extract_unsigned_field(mmfr0,
 						ID_AA64MMFR0_EL1_TGRAN64_SHIFT);
 
-	return (val >= ID_AA64MMFR0_EL1_TGRAN64_SUPPORTED_MIN) &&
-	       (val <= ID_AA64MMFR0_EL1_TGRAN64_SUPPORTED_MAX);
+	return IN_RANGE_INCLUSIVE(val,
+		ID_AA64MMFR0_EL1_TGRAN64_SUPPORTED_MIN,
+		ID_AA64MMFR0_EL1_TGRAN64_SUPPORTED_MAX);
 }
 
 static inline bool system_supports_16kb_granule(void)
@@ -719,8 +724,9 @@ static inline bool system_supports_16kb_granule(void)
 	val = cpuid_feature_extract_unsigned_field(mmfr0,
 						ID_AA64MMFR0_EL1_TGRAN16_SHIFT);
 
-	return (val >= ID_AA64MMFR0_EL1_TGRAN16_SUPPORTED_MIN) &&
-	       (val <= ID_AA64MMFR0_EL1_TGRAN16_SUPPORTED_MAX);
+	return IN_RANGE_INCLUSIVE(val,
+		ID_AA64MMFR0_EL1_TGRAN16_SUPPORTED_MIN,
+		ID_AA64MMFR0_EL1_TGRAN16_SUPPORTED_MAX);
 }
 
 static inline bool system_supports_mixed_endian_el0(void)
-- 
2.34.1