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From: Will Deacon <will@kernel.org>
To: Qian Cai <cai@lca.pw>
Cc: catalin.marinas@arm.com, rrichter@cavium.com,
	robin.murphy@arm.com, linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] arm64/prefetch: fix a -Wtype-limits warning
Date: Mon, 5 Aug 2019 11:00:59 +0100	[thread overview]
Message-ID: <20190805100059.4gml6c4kclz2iin3@willie-the-truck> (raw)
In-Reply-To: <20190803003358.992-1-cai@lca.pw>

On Fri, Aug 02, 2019 at 08:33:58PM -0400, Qian Cai wrote:
> 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@lca.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);	\

Hmm, but this really isn't a signed quantity: it's two fields extracted
from an ID register. I think the code is fine. Are you explicitly enabling
-Wtype-limits somehow?

Will

WARNING: multiple messages have this Message-ID (diff)
From: Will Deacon <will@kernel.org>
To: Qian Cai <cai@lca.pw>
Cc: rrichter@cavium.com, catalin.marinas@arm.com,
	robin.murphy@arm.com, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2] arm64/prefetch: fix a -Wtype-limits warning
Date: Mon, 5 Aug 2019 11:00:59 +0100	[thread overview]
Message-ID: <20190805100059.4gml6c4kclz2iin3@willie-the-truck> (raw)
In-Reply-To: <20190803003358.992-1-cai@lca.pw>

On Fri, Aug 02, 2019 at 08:33:58PM -0400, Qian Cai wrote:
> 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@lca.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);	\

Hmm, but this really isn't a signed quantity: it's two fields extracted
from an ID register. I think the code is fine. Are you explicitly enabling
-Wtype-limits somehow?

Will

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  reply	other threads:[~2019-08-05 10:01 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-03  0:33 [PATCH v2] arm64/prefetch: fix a -Wtype-limits warning Qian Cai
2019-08-03  0:33 ` Qian Cai
2019-08-05 10:00 ` Will Deacon [this message]
2019-08-05 10:00   ` Will Deacon
2019-08-05 12:03   ` Qian Cai
2019-08-05 12:03     ` Qian Cai
2019-08-05 17:03     ` Will Deacon
2019-08-05 17:03       ` Will Deacon

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