linux-kernel - Re: [PATCH v3] net: add Faraday FTMAC100 10/100 Ethernet driver

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Date:	Thu, 20 Jan 2011 23:54:35 +0800
From:	Po-Yu Chuang <ratbert.chuang@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	bhutchings@...arflare.com, joe@...ches.com, dilinger@...ued.net,
	Po-Yu Chuang <ratbert@...aday-tech.com>
Subject: Re: [PATCH v3] net: add Faraday FTMAC100 10/100 Ethernet driver

Dear Eric,

On Thu, Jan 20, 2011 at 11:41 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> Le jeudi 20 janvier 2011 à 23:30 +0800, Po-Yu Chuang a écrit :
>
>> +static bool ftmac100_tx_complete_packet(struct ftmac100 *priv)
>> +{
>> +     struct net_device *netdev = priv->netdev;
>> +     struct ftmac100_txdes *txdes;
>> +     struct sk_buff *skb;
>> +     dma_addr_t map;
>> +
>> +     if (priv->tx_pending == 0)
>> +             return false;
>> +
>> +     txdes = ftmac100_current_clean_txdes(priv);
>> +
>> +     if (ftmac100_txdes_owned_by_dma(txdes))
>> +             return false;
>> +
>> +     skb = ftmac100_txdes_get_skb(txdes);
>> +     map = ftmac100_txdes_get_dma_addr(txdes);
>> +
>> +     if (unlikely(ftmac100_txdes_excessive_collision(txdes) ||
>> +                  ftmac100_txdes_late_collision(txdes))) {
>> +             /*
>> +              * packet transmitted to ethernet lost due to late collision
>> +              * or excessive collision
>> +              */
>> +             netdev->stats.tx_aborted_errors++;
>> +     } else {
>> +             netdev->stats.tx_packets++;
>> +             netdev->stats.tx_bytes += skb->len;
>> +     }
>> +
>> +     dma_unmap_single(priv->dev, map, skb_headlen(skb), DMA_TO_DEVICE);
>> +
>> +     dev_kfree_skb_irq(skb);
>> +
>> +     ftmac100_txdes_reset(txdes);
>> +
>> +     ftmac100_tx_clean_pointer_advance(priv);
>> +
>> +     priv->tx_pending--;
>> +     netif_wake_queue(netdev);
>> +
>> +     return true;
>> +}
>> +
>> +static void ftmac100_tx_complete(struct ftmac100 *priv)
>> +{
>> +     unsigned long flags;
>> +
>> +     spin_lock_irqsave(&priv->tx_lock, flags);
>> +     while (ftmac100_tx_complete_packet(priv))
>> +             ;
>> +     spin_unlock_irqrestore(&priv->tx_lock, flags);
>> +}
>> +
>
> I dont understand why you still block hard IRQS, after full NAPI
> conversion.
>
> Now you run from NAPI, and softirq handler, are you sure you still need
> to block hard IRQ and tx_lock ?
>
> It seems to me ftmac100_xmit() could only block softirqs (but they
> already are blocked by caller), so you could use spin_lock() from
> ftmac100_xmit()

I was not quite clear about when to use what kinds of locking.
After your explanation, now I understand.
I will submit v4 tomorrow.

really appreciate,
Po-Yu Chuang
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