netdev - Re: [PATCH v4] lpc32xx: Added ethernet driver

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Date:	Tue, 06 Mar 2012 09:53:45 +0100
From:	Roland Stigge <stigge@...com.de>
To:	Ben Hutchings <bhutchings@...arflare.com>
CC:	davem@...emloft.net, jeffrey.t.kirsher@...el.com,
	alexander.h.duyck@...el.com, eilong@...adcom.com,
	ian.campbell@...rix.com, netdev@...r.kernel.org,
	w.sang@...gutronix.de, linux-kernel@...r.kernel.org,
	kevin.wells@....com, linux-arm-kernel@...ts.infradead.org,
	arnd@...db.de, baruch@...s.co.il, joe@...ches.com
Subject: Re: [PATCH v4] lpc32xx: Added ethernet driver

Hi Ben,

thank you for your review!

On 03/05/2012 11:45 PM, Ben Hutchings wrote:
> [...]
>> +static int lpc_eth_poll(struct napi_struct *napi, int budget)
>> +{
>> +	struct netdata_local *pldat = container_of(napi,
>> +			struct netdata_local, napi);
>> +	struct net_device *ndev = pldat->ndev;
>> +	unsigned long flags;
>> +	int rx_done = 0;
>> +
>> +	spin_lock_irqsave(&pldat->lock, flags);
>> +
>> +	__lpc_handle_xmit(ndev);
>> +	rx_done = __lpc_handle_recv(ndev, budget);
>> +
>> +	if (rx_done < budget) {
>> +		napi_complete(napi);
>> +		lpc_eth_enable_int(pldat->net_base);
>> +	}
>> +
>> +	spin_unlock_irqrestore(&pldat->lock, flags);
>
> This is really sad.  You implement NAPI but then take away most of the
> benefits of that by disabling interrupts.
>
> It looks like you could safely unlock pldat->lock before calling
> __lpc_handle_recv - nothing else manipulates RX queue state so no lock
> is required.
>
> As for the TX side, you can probably use the TX queue lock
> (__netif_tx_lock, __netif_tx_unlock) to serialise with
> lpc_eth_hard_start_xmit() and avoid taking pldat->lock in either
> __lpc_handle_xmit() or here.

Sounds reasonable, and will do it.

However, I implemented it from the example of
drivers/net/ethernet/via/via-velocity.c:velocity_poll() - is there a
good reason for doing it that way in the velocity driver or is it done
incorrectly there, also?

Thanks,

Roland
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