netdev - Re: KS8695: possible NAPI issue

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Date:	Sat, 06 Mar 2010 10:40:50 +0800
From:	"Figo.zhang" <figo1802@...il.com>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	Yegor Yefremov <yegorslists@...glemail.com>,
	Dick Hollenbeck <dick@...tplc.com>, netdev@...r.kernel.org,
	zealcook@...il.com
Subject: Re: KS8695: possible NAPI issue


> 
> One of the requirements for NAPI to work is that the IRQ is level triggered.
> Otherwise there can be a race between packet arrival and the end of
> NAPI processing:
> 
> static int ks8695_poll(struct napi_struct *napi, int budget)
> {
> 	struct ks8695_priv *ksp = container_of(napi, struct ks8695_priv, napi);
> 	unsigned long  work_done;
> 
> 	unsigned long isr = readl(KS8695_IRQ_VA + KS8695_INTEN);
> 	unsigned long mask_bit = 1 << ks8695_get_rx_enable_bit(ksp);
> 
> 	work_done = ks8695_rx(ksp, budget);
> 
> 	if (work_done < budget) {
> 		unsigned long flags;
> 		spin_lock_irqsave(&ksp->rx_lock, flags);
> >>> packet arrives >>
> 		/*enable rx interrupt*/
> 		writel(isr | mask_bit, KS8695_IRQ_VA + KS8695_INTEN);
> >>> or here >>
> 		__napi_complete(napi);
> 		spin_unlock_irqrestore(&ksp->rx_lock, flags);
> 

yes, it is right, it maybe a race condition. so you can motify
ks8695_poll() to try, like this:

		__napi_complete(napi);
		/*enable rx interrupt*/
		writel(isr | mask_bit, KS8695_IRQ_VA + KS8695_INTEN); 


Best,
Figo.zhang

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