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Date:	Mon, 16 Jun 2014 14:28:47 -0700
From:	Sören Brinkmann <soren.brinkmann@...inx.com>
To:	Jongsung Kim <neidhard.kim@....com>
CC:	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	"David S. Miller" <davem@...emloft.net>,
	Hayun Hwang <hwang.hayun@....com>,
	Youngkyu Choi <youngkyu7.choi@....com>
Subject: Re: [PATCH] net/cadence/macb: clear interrupts simply and correctly

On Thu, 2014-06-12 at 05:50PM +0900, Jongsung Kim wrote:
> The "Rx used bit read" interrupt is enabled but not cleared for some
> systems with the ISR (Interrupt Status Register) configured as clear-
> on-write. This interrupt may be asserted when the CPU does not handle
> Rx-complete interrupts for a long time. (e.g., if the CPU is stopped
> by debugger) Once asserted, it'll not be cleared, and the CPU will
> loop infinitly in the interrupt handler.
> 
> This patch forces to use a dedicated function for reading the ISR,
> and the function clears it if clear-on-write. So the ISR is always
> cleared after read, regardless of clear-on-write configuration.
> 
> Reported-by: Hayun Hwang <hwang.hayun@....com>
> Signed-off-by: Youngkyu Choi <youngkyu7.choi@....com>
> Signed-off-by: Jongsung Kim <neidhard.kim@....com>
> Tested-by: Hayun Hwang <hwang.hayun@....com>
> ---
>  drivers/net/ethernet/cadence/macb.c |   37 ++++++++++++++--------------------
>  1 files changed, 15 insertions(+), 22 deletions(-)
> 
[...]
> @@ -552,9 +562,6 @@ static void macb_tx_interrupt(struct macb *bp)
>  	status = macb_readl(bp, TSR);
>  	macb_writel(bp, TSR, status);
>  
> -	if (bp->caps & MACB_CAPS_ISR_CLEAR_ON_WRITE)
> -		macb_writel(bp, ISR, MACB_BIT(TCOMP));
> -
>  	netdev_vdbg(bp->dev, "macb_tx_interrupt status = 0x%03lx\n",
>  		(unsigned long)status);
>  
> @@ -883,13 +890,10 @@ static int macb_poll(struct napi_struct *napi, int budget)
>  
>  		/* Packets received while interrupts were disabled */
>  		status = macb_readl(bp, RSR);
> -		if (status) {
> -			if (bp->caps & MACB_CAPS_ISR_CLEAR_ON_WRITE)
> -				macb_writel(bp, ISR, MACB_BIT(RCOMP));
> +		if (status)
>  			napi_reschedule(napi);
> -		} else {
> +		else
>  			macb_writel(bp, IER, MACB_RX_INT_FLAGS);
> -		}
>  	}
>  
>  	/* TODO: Handle errors */
> @@ -903,7 +907,7 @@ static irqreturn_t macb_interrupt(int irq, void *dev_id)
>  	struct macb *bp = netdev_priv(dev);
>  	u32 status;
>  
> -	status = macb_readl(bp, ISR);
> +	status = macb_read_isr(bp);
>  
>  	if (unlikely(!status))
>  		return IRQ_NONE;
> @@ -928,8 +932,6 @@ static irqreturn_t macb_interrupt(int irq, void *dev_id)
>  			 * now.
>  			 */
>  			macb_writel(bp, IDR, MACB_RX_INT_FLAGS);
> -			if (bp->caps & MACB_CAPS_ISR_CLEAR_ON_WRITE)
> -				macb_writel(bp, ISR, MACB_BIT(RCOMP));
Shouldn't it be sufficient to replace 'MACB_BIT(RCOMP) with 'MACB_RX_INT_FLAGS'
to clear all the RX IRQ flags.

	Sören
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