linux-kernel - Re: [PATCH v6 4/4] drivers: net: Add APM X-Gene SoC ethernet driver support.

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Date:	Tue, 17 Jun 2014 13:07:42 -0700
From:	Iyappan Subramanian <isubramanian@....com>
To:	Florian Fainelli <f.fainelli@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	netdev <netdev@...r.kernel.org>, patches <patches@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"jcm@...hat.com" <jcm@...hat.com>,
	Keyur Chudgar <kchudgar@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Ravi Patel <rapatel@....com>
Subject: Re: [PATCH v6 4/4] drivers: net: Add APM X-Gene SoC ethernet driver support.

On Tue, Jun 17, 2014 at 12:24 PM, Florian Fainelli <f.fainelli@...il.com> wrote:
> 2014-06-17 12:21 GMT-07:00 Iyappan Subramanian <isubramanian@....com>:
>> On Mon, Jun 16, 2014 at 9:42 PM, David Miller <davem@...emloft.net> wrote:
>>> From: Iyappan Subramanian <isubramanian@....com>
>>> Date: Mon, 16 Jun 2014 17:18:46 -0700
>>>
>>>> +static netdev_tx_t xgene_enet_start_xmit(struct sk_buff *skb,
>>>> +                                      struct net_device *ndev)
>>>> +{
>>>> +     struct xgene_enet_pdata *pdata = netdev_priv(ndev);
>>>> +     struct xgene_enet_desc_ring *tx_ring = pdata->tx_ring;
>>>> +     struct xgene_enet_desc_ring *cp_ring = tx_ring->cp_ring;
>>>> +     u32 tx_level, cq_level;
>>>> +
>>>> +     tx_level = xgene_enet_ring_len(tx_ring);
>>>> +     cq_level = xgene_enet_ring_len(cp_ring);
>>>> +     if (unlikely(tx_level > pdata->tx_qcnt_hi ||
>>>> +                  cq_level > pdata->cp_qcnt_hi)) {
>>>> +             netif_stop_queue(ndev);
>>>> +             return NETDEV_TX_BUSY;
>>>> +     }
>>>> +
>>>> +     if (xgene_enet_setup_tx_desc(tx_ring, skb))
>>>> +             return NETDEV_TX_OK;
>>>
>>> If you return NETDEV_TX_OK, it is your responsibility to deal with the
>>> SKB, because you own it.
>>>
>>> In particular, you have to free the packet.
>>
>> skb freeing happens in xgene_enet_tx_completion().
>
> I have not looked at what xgenet_enet_setup_tx_desc() does, but
> David's point is that, if this function fails and has not yet been
> able to queue the SKB for transmission at the HW, you should make sure
> that you free the SKB. Is xgene_enet_tx_completion() called if the
> driver failed to prepare a descriptor for a SKB?

Thanks for the explanation.  I will free up skb when
xgene_enet_setup_tx_desc() fails
and submit the next patch shortly.

> --
> Florian
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