linux-kernel - Re: [PATCH] net: macb: Remove redundant assignment to w0

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Message-ID: <80a97aa9-0bf4-d6c5-597e-4440b07ecdaf@microchip.com>
Date:   Thu, 29 Apr 2021 18:55:11 +0200
From:   Nicolas Ferre <nicolas.ferre@...rochip.com>
To:     Jiapeng Chong <jiapeng.chong@...ux.alibaba.com>,
        Rafal Ozieblo <rafalo@...ence.com>
CC:     <claudiu.beznea@...rochip.com>, <davem@...emloft.net>,
        <kuba@...nel.org>, <linux@...linux.org.uk>, <palmer@...belt.com>,
        <paul.walmsley@...ive.com>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-riscv@...ts.infradead.org>,
        Michal Simek <michal.simek@...inx.com>
Subject: Re: [PATCH] net: macb: Remove redundant assignment to w0

On 29/04/2021 at 12:26, Jiapeng Chong wrote:
> Variable w0 is set to zero but these values is not used as it is
> overwritten later on, hence redundant assignment can be removed.
> 
> Cleans up the following clang-analyzer warning:
> 
> drivers/net/ethernet/cadence/macb_main.c:3265:3: warning: Value stored
> to 'w0' is never read [clang-analyzer-deadcode.DeadStores].
> 
> drivers/net/ethernet/cadence/macb_main.c:3251:3: warning: Value stored
> to 'w0' is never read [clang-analyzer-deadcode.DeadStores].
> 
> Reported-by: Abaci Robot <abaci@...ux.alibaba.com>
> Signed-off-by: Jiapeng Chong <jiapeng.chong@...ux.alibaba.com>

NACK: there seems to be a massive bug in this code as I have the strong 
feeling that '=' must be replaces by '|=' in subsequent assignment of 
w0, W1... otherwise I don't understand the meaning of all this!

I don't know how RX filtering must be done in this controller neither 
how to test it so if nobody steps in to fix this, I'll probably have to 
do a patch based on datasheet only.

Please comment if you have a view on this.

Best regards,
   Nicolas

> ---
>   drivers/net/ethernet/cadence/macb_main.c | 2 --
>   1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
> index 0f6a6cb..741b2e3 100644
> --- a/drivers/net/ethernet/cadence/macb_main.c
> +++ b/drivers/net/ethernet/cadence/macb_main.c
> @@ -3248,7 +3248,6 @@ static void gem_prog_cmp_regs(struct macb *bp, struct ethtool_rx_flow_spec *fs)
>          /* ignore field if any masking set */
>          if (tp4sp_m->ip4src == 0xFFFFFFFF) {
>                  /* 1st compare reg - IP source address */
> -               w0 = 0;
>                  w1 = 0;
>                  w0 = tp4sp_v->ip4src;
>                  w1 = GEM_BFINS(T2DISMSK, 1, w1); /* 32-bit compare */
> @@ -3262,7 +3261,6 @@ static void gem_prog_cmp_regs(struct macb *bp, struct ethtool_rx_flow_spec *fs)
>          /* ignore field if any masking set */
>          if (tp4sp_m->ip4dst == 0xFFFFFFFF) {
>                  /* 2nd compare reg - IP destination address */
> -               w0 = 0;
>                  w1 = 0;
>                  w0 = tp4sp_v->ip4dst;
>                  w1 = GEM_BFINS(T2DISMSK, 1, w1); /* 32-bit compare */
> --
> 1.8.3.1
> 


-- 
Nicolas Ferre