linux-kernel - Re: [PATCH v2] net: add Faraday FTMAC100 10/100 Ethernet driver

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Message-ID: <AANLkTikDkvcDhjEpVL+VK=UTHb5M19Mw167R_z0QwDVW@mail.gmail.com>
Date:	Wed, 19 Jan 2011 17:20:38 +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,
	ratbert@...aday-tech.com, bhutchings@...arflare.com,
	joe@...ches.com, dilinger@...ued.net
Subject: Re: [PATCH v2] net: add Faraday FTMAC100 10/100 Ethernet driver

Dear Eric,

On Tue, Jan 18, 2011 at 2:21 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> Le lundi 17 janvier 2011 à 17:21 +0800, Po-Yu Chuang a écrit :
>> +     spin_lock_irqsave(&priv->tx_lock, flags);
>> +     ftmac100_txdes_set_skb(txdes, skb);
>> +     ftmac100_txdes_set_dma_addr(txdes, map);
>> +
>> +     ftmac100_txdes_set_first_segment(txdes);
>> +     ftmac100_txdes_set_last_segment(txdes);
>> +     ftmac100_txdes_set_txint(txdes);
>> +     ftmac100_txdes_set_buffer_size(txdes, len);
>
> I wonder if its not too expensive to read/modify/write txdes->txdes1
>
> Maybe you should use a temporary u32 var and perform one final write on
> txdes->txdes1 (with the set_dma_own)

That's OK, the compiler combines these bits updates together and write once
since txdes is not volatile. (I checked the object file)
It's not expensive.

BTW, DMA_OWN bit is at txdes0

>> +     priv->tx_pending++;
>> +     if (priv->tx_pending == TX_QUEUE_ENTRIES) {
>> +             if (net_ratelimit())
>> +                     netdev_info(netdev, "tx queue full\n");
>> +
>> +             netif_stop_queue(netdev);
>> +     }
>> +
>> +     /* start transmit */
>> +     ftmac100_txdes_set_dma_own(txdes);
>
>        txdes->txdes1 = txdes1;
>
> BTW, shouldnt you use cpu_to_be32() or cpu_to_le32(), if this driver is
> multi platform ?

OK, but I am not sure if I use them the right way.
Please check my v3 patch later.

Thanks,
Po-Yu Chuang
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