linux-kernel - Re: [PATCH] ASoC: mchp-spdiftx: Fix clang -Wbitfield-constant-conversion

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Message-ID: <CAKwvOdmZvB_=JTeLg08uMFhEMpWga4FJey50QHjzCv_jMVpwkg@mail.gmail.com>
Date:   Wed, 10 Aug 2022 14:14:16 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Codrin Ciubotariu <codrin.ciubotariu@...rochip.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Claudiu Beznea <claudiu.beznea@...rochip.com>,
        Tom Rix <trix@...hat.com>, alsa-devel@...a-project.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH] ASoC: mchp-spdiftx: Fix clang -Wbitfield-constant-conversion

On Tue, Aug 9, 2022 at 6:08 PM Nathan Chancellor <nathan@...nel.org> wrote:
>
> A recent change in clang strengthened its -Wbitfield-constant-conversion
> to warn when 1 is assigned to a 1-bit signed integer bitfield, as it can
> only be 0 or -1, not 1:
>
>   sound/soc/atmel/mchp-spdiftx.c:505:20: error: implicit truncation from 'int' to bit-field changes value from 1 to -1 [-Werror,-Wbitfield-constant-conversion]
>           dev->gclk_enabled = 1;
>                             ^ ~
>   1 error generated.
>
> The actual value of the field is never checked, just that it is not
> zero, so there is not a real bug here. However, it is simple enough to
> silence the warning by making the bitfield unsigned, which matches the
> mchp-spdifrx driver.
>
> Fixes: 06ca24e98e6b ("ASoC: mchp-spdiftx: add driver for S/PDIF TX Controller")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1686
> Link: https://github.com/llvm/llvm-project/commit/82afc9b169a67e8b8a1862fb9c41a2cd974d6691
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>

Ah yes, my favorite, signed one bit integers...thanks for the patch.
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

grepping for `gclk_enabled`, we see three drivers with similar
duplication (single bit bitfields):

sound/soc/atmel/mchp-spdifrx.c
241: unsigned int gclk_enabled:1;

sound/soc/atmel/mchp-pdmc.c
118: u8 gclk_enabled:1;

sound/soc/atmel/mchp-spdiftx.c
200: int gclk_enabled:1;

> ---
>  sound/soc/atmel/mchp-spdiftx.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/sound/soc/atmel/mchp-spdiftx.c b/sound/soc/atmel/mchp-spdiftx.c
> index 4850a177803d..ab2d7a791f39 100644
> --- a/sound/soc/atmel/mchp-spdiftx.c
> +++ b/sound/soc/atmel/mchp-spdiftx.c
> @@ -196,7 +196,7 @@ struct mchp_spdiftx_dev {
>         struct clk                              *pclk;
>         struct clk                              *gclk;
>         unsigned int                            fmt;
> -       int                                     gclk_enabled:1;
> +       unsigned int                            gclk_enabled:1;
>  };
>
>  static inline int mchp_spdiftx_is_running(struct mchp_spdiftx_dev *dev)
>
> base-commit: 15205c2829ca2cbb5ece5ceaafe1171a8470e62b
> --
> 2.37.1
>


-- 
Thanks,
~Nick Desaulniers