linux-kernel - Re: [PATCH] net: ethernet: sun: Remove redundant code

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Date:   Thu, 3 Mar 2022 15:22:43 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Jiapeng Chong <jiapeng.chong@...ux.alibaba.com>
Cc:     davem@...emloft.net, kuba@...nel.org, gustavoars@...nel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Abaci Robot <abaci@...ux.alibaba.com>
Subject: Re: [PATCH] net: ethernet: sun: Remove redundant code

On Thu, Mar 03, 2022 at 05:14:40PM +0800, Jiapeng Chong wrote:
> Because CAS_FLAG_REG_PLUS is assigned a value of 1, it never enters
> these for loops.

Please can you expand this comment, it is not clear to my what you
mean here. When i look at:

/* check pci invariants */
static void cas_check_pci_invariants(struct cas *cp)
{
        struct pci_dev *pdev = cp->pdev;

        cp->cas_flags = 0;
        if ((pdev->vendor == PCI_VENDOR_ID_SUN) &&
            (pdev->device == PCI_DEVICE_ID_SUN_CASSINI)) {
                if (pdev->revision >= CAS_ID_REVPLUS)
                        cp->cas_flags |= CAS_FLAG_REG_PLUS;

it is not obvious why it could not enter these loops.

   Andrew

> 
> Clean up the following smatch warning:
> 
> drivers/net/ethernet/sun/cassini.c:3513 cas_start_dma() warn: we never
> enter this loop.
> 
> drivers/net/ethernet/sun/cassini.c:1239 cas_init_rx_dma() warn: we never
> enter this loop.
> 
> drivers/net/ethernet/sun/cassini.c:1247 cas_init_rx_dma() warn: we never
> enter this loop.
> 
> Reported-by: Abaci Robot <abaci@...ux.alibaba.com>
> Signed-off-by: Jiapeng Chong <jiapeng.chong@...ux.alibaba.com>
> ---
>  drivers/net/ethernet/sun/cassini.c | 16 ----------------
>  1 file changed, 16 deletions(-)
> 
> diff --git a/drivers/net/ethernet/sun/cassini.c b/drivers/net/ethernet/sun/cassini.c
> index 947a76a788c7..153edc5eadad 100644
> --- a/drivers/net/ethernet/sun/cassini.c
> +++ b/drivers/net/ethernet/sun/cassini.c
> @@ -1235,19 +1235,6 @@ static void cas_init_rx_dma(struct cas *cp)
>  	 */
>  	readl(cp->regs + REG_INTR_STATUS_ALIAS);
>  	writel(INTR_RX_DONE | INTR_RX_BUF_UNAVAIL, cp->regs + REG_ALIAS_CLEAR);
> -	if (cp->cas_flags & CAS_FLAG_REG_PLUS) {
> -		for (i = 1; i < N_RX_COMP_RINGS; i++)
> -			readl(cp->regs + REG_PLUS_INTRN_STATUS_ALIAS(i));
> -
> -		/* 2 is different from 3 and 4 */
> -		if (N_RX_COMP_RINGS > 1)
> -			writel(INTR_RX_DONE_ALT | INTR_RX_BUF_UNAVAIL_1,
> -			       cp->regs + REG_PLUS_ALIASN_CLEAR(1));
> -
> -		for (i = 2; i < N_RX_COMP_RINGS; i++)
> -			writel(INTR_RX_DONE_ALT,
> -			       cp->regs + REG_PLUS_ALIASN_CLEAR(i));
> -	}
>  
>  	/* set up pause thresholds */
>  	val  = CAS_BASE(RX_PAUSE_THRESH_OFF,
> @@ -3509,9 +3496,6 @@ static inline void cas_start_dma(struct cas *cp)
>  		if (N_RX_DESC_RINGS > 1)
>  			writel(RX_DESC_RINGN_SIZE(1) - 4,
>  			       cp->regs + REG_PLUS_RX_KICK1);
> -
> -		for (i = 1; i < N_RX_COMP_RINGS; i++)
> -			writel(0, cp->regs + REG_PLUS_RX_COMPN_TAIL(i));
>  	}
>  }
>  
> -- 
> 2.20.1.7.g153144c
>