Re: [PATCH v6 1/3] phy: mediatek: fix build warning caused by clang

Nick Desaulniers
2023-01-13T18:37:47Z

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