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 <20190813173448.109859-1-nhuck@google.com>
In-Reply-To: <20190813173448.109859-1-nhuck@google.com>
From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Tue, 13 Aug 2019 13:43:03 -0700
Message-ID: <CAKwvOdmFc3RfHMVxdym9upmck=h6AnNW58ho+0ferOUVkaxajw@mail.gmail.com>
Subject: Re: [PATCH v2] dmaengine: mv_xor_v2: Fix -Wshift-negative-value
To:     Nathan Huckleberry <nhuck@google.com>
Cc:     Dan Williams <dan.j.williams@intel.com>,
        Vinod Koul <vkoul@kernel.org>, dmaengine@vger.kernel.org,
        LKML <linux-kernel@vger.kernel.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>
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Sender: linux-kernel-owner@vger.kernel.org
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On Tue, Aug 13, 2019 at 10:35 AM 'Nathan Huckleberry' via Clang Built
Linux <clang-built-linux@googlegroups.com> wrote:
>
> Clang produces the following warning
>
> drivers/dma/mv_xor_v2.c:264:40: warning: shifting a negative signed value
>         is undefined [-Wshift-negative-value]
>         reg &= (~MV_XOR_V2_DMA_IMSG_THRD_MASK <<
>         MV_XOR_V2_DMA_IMSG_THRD_SHIFT);
>                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^
> drivers/dma/mv_xor_v2.c:271:46: warning: shifting a negative signed value
>         is undefined [-Wshift-negative-value]
>         reg &= (~MV_XOR_V2_DMA_IMSG_TIMER_THRD_MASK <<
>                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^
>
> Upon further investigation MV_XOR_V2_DMA_IMSG_THRD_SHIFT and
> MV_XOR_V2_DMA_IMSG_TIMER_THRD_SHIFT are both 0. Since shifting by 0 does
> nothing, these variables can be removed.
>
> Cc: clang-built-linux@googlegroups.com
> Link: https://github.com/ClangBuiltLinux/linux/issues/521
> Signed-off-by: Nathan Huckleberry <nhuck@google.com>

Thanks for sending a v2:
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

> ---
>  drivers/dma/mv_xor_v2.c | 11 ++++-------
>  1 file changed, 4 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/dma/mv_xor_v2.c b/drivers/dma/mv_xor_v2.c
> index fa5dab481203..e3850f04f676 100644
> --- a/drivers/dma/mv_xor_v2.c
> +++ b/drivers/dma/mv_xor_v2.c
> @@ -33,7 +33,6 @@
>  #define MV_XOR_V2_DMA_IMSG_CDAT_OFF                    0x014
>  #define MV_XOR_V2_DMA_IMSG_THRD_OFF                    0x018
>  #define   MV_XOR_V2_DMA_IMSG_THRD_MASK                 0x7FFF
> -#define   MV_XOR_V2_DMA_IMSG_THRD_SHIFT                        0x0
>  #define   MV_XOR_V2_DMA_IMSG_TIMER_EN                  BIT(18)
>  #define MV_XOR_V2_DMA_DESQ_AWATTR_OFF                  0x01C
>    /* Same flags as MV_XOR_V2_DMA_DESQ_ARATTR_OFF */
> @@ -50,7 +49,6 @@
>  #define MV_XOR_V2_DMA_DESQ_ADD_OFF                     0x808
>  #define MV_XOR_V2_DMA_IMSG_TMOT                                0x810
>  #define   MV_XOR_V2_DMA_IMSG_TIMER_THRD_MASK           0x1FFF
> -#define   MV_XOR_V2_DMA_IMSG_TIMER_THRD_SHIFT          0
>
>  /* XOR Global registers */
>  #define MV_XOR_V2_GLOB_BW_CTRL                         0x4
> @@ -261,16 +259,15 @@ void mv_xor_v2_enable_imsg_thrd(struct mv_xor_v2_device *xor_dev)
>
>         /* Configure threshold of number of descriptors, and enable timer */
>         reg = readl(xor_dev->dma_base + MV_XOR_V2_DMA_IMSG_THRD_OFF);
> -       reg &= (~MV_XOR_V2_DMA_IMSG_THRD_MASK << MV_XOR_V2_DMA_IMSG_THRD_SHIFT);
> -       reg |= (MV_XOR_V2_DONE_IMSG_THRD << MV_XOR_V2_DMA_IMSG_THRD_SHIFT);
> +       reg &= ~MV_XOR_V2_DMA_IMSG_THRD_MASK;
> +       reg |= MV_XOR_V2_DONE_IMSG_THRD;
>         reg |= MV_XOR_V2_DMA_IMSG_TIMER_EN;
>         writel(reg, xor_dev->dma_base + MV_XOR_V2_DMA_IMSG_THRD_OFF);
>
>         /* Configure Timer Threshold */
>         reg = readl(xor_dev->dma_base + MV_XOR_V2_DMA_IMSG_TMOT);
> -       reg &= (~MV_XOR_V2_DMA_IMSG_TIMER_THRD_MASK <<
> -               MV_XOR_V2_DMA_IMSG_TIMER_THRD_SHIFT);
> -       reg |= (MV_XOR_V2_TIMER_THRD << MV_XOR_V2_DMA_IMSG_TIMER_THRD_SHIFT);
> +       reg &= ~MV_XOR_V2_DMA_IMSG_TIMER_THRD_MASK;
> +       reg |= MV_XOR_V2_TIMER_THRD;
>         writel(reg, xor_dev->dma_base + MV_XOR_V2_DMA_IMSG_TMOT);
>  }
>
> --
> 2.23.0.rc1.153.gdeed80330f-goog
>
> --
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-- 
Thanks,
~Nick Desaulniers