linux-kernel - Re: [PATCH] net: macb: Change interrupt and napi enable order in open

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Date:   Tue, 7 May 2019 15:32:33 +0000
From:   <Nicolas.Ferre@...rochip.com>
To:     <harini.katakam@...inx.com>, <davem@...emloft.net>,
        <rafalo@...ence.com>
CC:     <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <michal.simek@...inx.com>, <harinikatakamlinux@...il.com>
Subject: Re: [PATCH] net: macb: Change interrupt and napi enable order in open

On 07/05/2019 at 16:29, Harini Katakam wrote:
> External E-Mail
> 
> 
> Current order in open:
> -> Enable interrupts (macb_init_hw)
> -> Enable NAPI
> -> Start PHY
> 
> Sequence of RX handling:
> -> RX interrupt occurs
> -> Interrupt is cleared and interrupt bits disabled in handler
> -> NAPI is scheduled
> -> In NAPI, RX budget is processed and RX interrupts are re-enabled
> 
> With the above, on QEMU or fixed link setups (where PHY state doesn't
> matter), there's a chance macb RX interrupt occurs before NAPI is
> enabled. This will result in NAPI being scheduled before it is enabled.
> Fix this macb open by changing the order.
> 
> Fixes: ae1f2a56d273 ("net: macb: Added support for many RX queues")
> Signed-off-by: Harini Katakam <harini.katakam@...inx.com>

it looks okay to me:
Acked-by: Nicolas Ferre <nicolas.ferre@...rochip.com>

> ---
>   drivers/net/ethernet/cadence/macb_main.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
> index 5d5c9d7..c049410 100644
> --- a/drivers/net/ethernet/cadence/macb_main.c
> +++ b/drivers/net/ethernet/cadence/macb_main.c
> @@ -2427,12 +2427,12 @@ static int macb_open(struct net_device *dev)
>   		goto pm_exit;
>   	}
>   
> -	bp->macbgem_ops.mog_init_rings(bp);
> -	macb_init_hw(bp);
> -
>   	for (q = 0, queue = bp->queues; q < bp->num_queues; ++q, ++queue)
>   		napi_enable(&queue->napi);
>   
> +	bp->macbgem_ops.mog_init_rings(bp);
> +	macb_init_hw(bp);
> +
>   	/* schedule a link state check */
>   	phy_start(dev->phydev);
>   
> 


-- 
Nicolas Ferre