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References: <20230104132646.7100-1-chunfeng.yun@mediatek.com>
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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Fri, 13 Jan 2023 10:36:27 -0800
Message-ID: <CAKwvOdnMF4LRhTnQ3Rg+q3hd7jm2tS0aTHmwU6isKJHL2u9Q-g@mail.gmail.com>
Subject: Re: [PATCH v6 1/3] phy: mediatek: fix build warning caused by clang
To:     Chunfeng Yun <chunfeng.yun@mediatek.com>
Cc:     Vinod Koul <vkoul@kernel.org>,
        Kishon Vijay Abraham I <kishon@kernel.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Nathan Chancellor <nathan@kernel.org>,
        Tom Rix <trix@redhat.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>,
        linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org, linux-phy@lists.infradead.org,
        linux-kernel@vger.kernel.org, llvm@lists.linux.dev,
        Eddie Hung <eddie.hung@mediatek.com>,
        kernel test robot <lkp@intel.com>,
        Arnd Bergmann <arnd@arndb.de>
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On Wed, Jan 4, 2023 at 5:26 AM Chunfeng Yun <chunfeng.yun@mediatek.com> wrote:
>
> Remove the temporary @mask_, this may cause build warning when use clang
> compiler for powerpc, but can't reproduce it when compile for arm64.
> the build warning is -Wtautological-constant-out-of-range-compare, and
> caused by
> "BUILD_BUG_ON_MSG(__bf_cast_unsigned(_mask, _mask)"

Can you please include the text of the observed warning?

>
> After removing @mask_, there is a "CHECK:MACRO_ARG_REUSE" when run
> checkpatch.pl, due to @mask is constant, no reuse problem will happen.
>
> Fixes: 84513eccd678 ("phy: mediatek: fix build warning of FIELD_PREP()")

Uh, why was 84513eccd678 sent/reviewed/merged if it didn't fix the
issue correctly in the first place?

Is the issue perhaps that your mask isn't wide enough in the first
place, and should be?  See:
commit cfd6fb45cfaf ("crypto: ccree - avoid out-of-range warnings from clang")
for inspiration.

> Reported-by: kernel test robot <lkp@intel.com>

Can you please include the Link: tag to the lore URL of the report?

> Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
> ---
> v6: modify the title
> v5: no changes
> v4 new patch, I'm not sure it can fix build warning, due to I don't cross compile
>     it for powerpc using clang in office.
> ---
>  drivers/phy/mediatek/phy-mtk-io.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/phy/mediatek/phy-mtk-io.h b/drivers/phy/mediatek/phy-mtk-io.h
> index d20ad5e5be81..58f06db822cb 100644
> --- a/drivers/phy/mediatek/phy-mtk-io.h
> +++ b/drivers/phy/mediatek/phy-mtk-io.h
> @@ -39,8 +39,8 @@ static inline void mtk_phy_update_bits(void __iomem *reg, u32 mask, u32 val)
>  /* field @mask shall be constant and continuous */
>  #define mtk_phy_update_field(reg, mask, val) \
>  ({ \
> -       typeof(mask) mask_ = (mask);    \
> -       mtk_phy_update_bits(reg, mask_, FIELD_PREP(mask_, val)); \
> +       BUILD_BUG_ON_MSG(!__builtin_constant_p(mask), "mask is not constant"); \
> +       mtk_phy_update_bits(reg, mask, FIELD_PREP(mask, val)); \
>  })
>
>  #endif
> --
> 2.18.0
>


-- 
Thanks,
~Nick Desaulniers