linux-kernel - Re: [PATCH] soc/tegra: fuse: Fix bitwise vs. logical OR warning

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Date:   Wed, 17 Nov 2021 10:21:05 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, Anders Roxell <anders.roxell@...aro.org>
Subject: Re: [PATCH] soc/tegra: fuse: Fix bitwise vs. logical OR warning

+ Anders (combining
https://lore.kernel.org/all/20211117142115.694316-1-anders.roxell@linaro.org/).

On Thu, Oct 21, 2021 at 2:45 PM Nathan Chancellor <nathan@...nel.org> wrote:
>
> A new warning in clang points out two instances where boolean
> expressions are being used with a bitwise OR instead of logical OR:
>
> drivers/soc/tegra/fuse/speedo-tegra20.c:72:9: warning: use of bitwise '|' with boolean operands [-Wbitwise-instead-of-logical]
>                 reg = tegra_fuse_read_spare(i) |
>                       ^~~~~~~~~~~~~~~~~~~~~~~~~~
>                                                ||
> drivers/soc/tegra/fuse/speedo-tegra20.c:72:9: note: cast one or both operands to int to silence this warning
> drivers/soc/tegra/fuse/speedo-tegra20.c:87:9: warning: use of bitwise '|' with boolean operands [-Wbitwise-instead-of-logical]
>                 reg = tegra_fuse_read_spare(i) |
>                       ^~~~~~~~~~~~~~~~~~~~~~~~~~
>                                                ||
> drivers/soc/tegra/fuse/speedo-tegra20.c:87:9: note: cast one or both operands to int to silence this warning
> 2 warnings generated.
>
> The motivation for the warning is that logical operations short circuit
> while bitwise operations do not. In this case, it does not seem like
> short circuiting is harmful so implement the suggested fix of changing
> to a logical operation to fix the warning.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1488
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>

Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
Fixes: 25cd5a391478 ("ARM: tegra: Add speedo-based process identification")

> ---
>  drivers/soc/tegra/fuse/speedo-tegra20.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/soc/tegra/fuse/speedo-tegra20.c b/drivers/soc/tegra/fuse/speedo-tegra20.c
> index 2546bddbab93..4984246605ae 100644
> --- a/drivers/soc/tegra/fuse/speedo-tegra20.c
> +++ b/drivers/soc/tegra/fuse/speedo-tegra20.c
> @@ -69,7 +69,7 @@ void __init tegra20_init_speedo_data(struct tegra_sku_info *sku_info)
>
>         val = 0;
>         for (i = CPU_SPEEDO_MSBIT; i >= CPU_SPEEDO_LSBIT; i--) {
> -               reg = tegra_fuse_read_spare(i) |
> +               reg = tegra_fuse_read_spare(i) ||
>                         tegra_fuse_read_spare(i + CPU_SPEEDO_REDUND_OFFS);
>                 val = (val << 1) | (reg & 0x1);
>         }
> @@ -84,7 +84,7 @@ void __init tegra20_init_speedo_data(struct tegra_sku_info *sku_info)
>
>         val = 0;
>         for (i = SOC_SPEEDO_MSBIT; i >= SOC_SPEEDO_LSBIT; i--) {
> -               reg = tegra_fuse_read_spare(i) |
> +               reg = tegra_fuse_read_spare(i) ||
>                         tegra_fuse_read_spare(i + SOC_SPEEDO_REDUND_OFFS);
>                 val = (val << 1) | (reg & 0x1);
>         }
>
> base-commit: 519d81956ee277b4419c723adfb154603c2565ba
> --
> 2.33.1.637.gf443b226ca
>


-- 
Thanks,
~Nick Desaulniers