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Subject: Re: [PATCH v2 1/1] net: macb: ensure ordering write to re-enable RX
 smoothly
To: Zumeng Chen <zumeng.chen@windriver.com>
References: <1480341300-17384-1-git-send-email-zumeng.chen@windriver.com>
CC: <davem@davemloft.net>, <netdev@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>,
        Cyrille Pitchen <cyrille.pitchen@atmel.com>,
        Andrei Pistirica <Andrei.Pistirica@microchip.com>
From: Nicolas Ferre <nicolas.ferre@atmel.com>
Organization: atmel
Message-ID: <3d22926d-e892-e824-4bee-a52b4945f9ed@atmel.com>
Date: Mon, 28 Nov 2016 15:04:15 +0100
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Le 28/11/2016 ? 14:55, Zumeng Chen a ?crit :
> When a hardware issue happened as described by inline comments, the register
> write pattern looks like the following:
> 
> <write ~MACB_BIT(RE)>
> + wmb();
> <write MACB_BIT(RE)>
> 
> There might be a memory barrier between these two write operations, so add wmb
> to ensure an flip from 0 to 1 for NCR.
> 
> Signed-off-by: Zumeng Chen <zumeng.chen@windriver.com>

Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>

Thanks, best regards,

> ---
> 
> V2 changes:
> 
> Add the same wmb for at91ether as well based on reviewer's suggestion.
> 
> Cheers,
>  drivers/net/ethernet/cadence/macb.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/net/ethernet/cadence/macb.c b/drivers/net/ethernet/cadence/macb.c
> index 533653b..6d7cfa7 100644
> --- a/drivers/net/ethernet/cadence/macb.c
> +++ b/drivers/net/ethernet/cadence/macb.c
> @@ -1156,6 +1156,7 @@ static irqreturn_t macb_interrupt(int irq, void *dev_id)
>  		if (status & MACB_BIT(RXUBR)) {
>  			ctrl = macb_readl(bp, NCR);
>  			macb_writel(bp, NCR, ctrl & ~MACB_BIT(RE));
> +			wmb();
>  			macb_writel(bp, NCR, ctrl | MACB_BIT(RE));
>  
>  			if (bp->caps & MACB_CAPS_ISR_CLEAR_ON_WRITE)
> @@ -2770,6 +2771,7 @@ static irqreturn_t at91ether_interrupt(int irq, void *dev_id)
>  	if (intstatus & MACB_BIT(RXUBR)) {
>  		ctl = macb_readl(lp, NCR);
>  		macb_writel(lp, NCR, ctl & ~MACB_BIT(RE));
> +		wmb();
>  		macb_writel(lp, NCR, ctl | MACB_BIT(RE));
>  	}
>  
> 


-- 
Nicolas Ferre