linux-kernel - Re: [PATCH] MIPS: Compare __SYNC_loongson3

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Date:   Fri, 15 Jan 2021 15:39:01 +0100
From:   Thomas Bogendoerfer <tsbogend@...ha.franken.de>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] MIPS: Compare __SYNC_loongson3_war against 0

On Thu, Jan 14, 2021 at 10:34:16AM -0700, Nathan Chancellor wrote:
> When building with clang when CONFIG_CPU_LOONGSON3_WORKAROUNDS is
> enabled:
> 
>  In file included from lib/errseq.c:4:
>  In file included from ./include/linux/atomic.h:7:
>  ./arch/mips/include/asm/atomic.h:52:1: warning: converting the result of
>  '<<' to a boolean always evaluates to true
>  [-Wtautological-constant-compare]
>  ATOMIC_OPS(atomic64, s64)
>  ^
>  ./arch/mips/include/asm/atomic.h:40:9: note: expanded from macro
>  'ATOMIC_OPS'
>          return cmpxchg(&v->counter, o, n);
>                 ^
>  ./arch/mips/include/asm/cmpxchg.h:194:7: note: expanded from macro
>  'cmpxchg'
>          if (!__SYNC_loongson3_war)
>               ^
>  ./arch/mips/include/asm/sync.h:147:34: note: expanded from macro
>  '__SYNC_loongson3_war'
>  # define __SYNC_loongson3_war   (1 << 31)
>                                     ^
> 
> While it is not wrong that the result of this shift is always true in a
> boolean context, it is not a problem here. Regardless, the warning is
> really noisy so rather than making the shift a boolean implicitly, use
> it in an equality comparison so the shift is used as an integer value.
> 
> Fixes: 4d1dbfe6cbec ("MIPS: atomic: Emit Loongson3 sync workarounds within asm")
> Fixes: a91f2a1dba44 ("MIPS: cmpxchg: Omit redundant barriers for Loongson3")
> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> ---
>  arch/mips/include/asm/atomic.h  | 2 +-
>  arch/mips/include/asm/cmpxchg.h | 6 +++---
>  2 files changed, 4 insertions(+), 4 deletions(-)

applied ti mips-next.

Thomas.

-- 
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