Subject: Re: [PATCH v8 3/3] net: hisilicon: new hip04 ethernet driver

From: Ding Tianhong <[email-masked]>
Date: Wed, 10 Dec 2014 11:51:51 +0800

On 2014/12/8 4:09, Arnd Bergmann wrote:
> On Sunday 07 December 2014 10:49:12 Alexander Graf wrote:
>> On 07.12.14 04:28, Ding Tianhong wrote:
>>> On 2014/12/7 8:42, Alexander Graf wrote:
>>>> On 19.04.14 03:13, Zhangfei Gao wrote:
>>>>> Support Hisilicon hip04 ethernet driver, including 100M / 1000M controller.
>>>>> The controller has no tx done interrupt, reclaim xmitted buffer in the poll.
>>>>>
>>>>> Signed-off-by: Zhangfei Gao <[email-masked]>
>>>>
>>>> Is this driver still supposed to go upstream? I presume this was the
>>>> last submission and it's been quite some time ago 
>>>>
>>>
>>> yes, it is really a long time, but The hip04 did not support tx irq, 
>>> we couldn't get any better idea to fix this defect, do you have any suggestion?
>>
>> Well, if hardware doesn't have a TX irq I don't see there's anything we
>> can do to fix that ;).
> 
> I don't know if it's related to the ethernet on hip01, but I would assume
> it is, and that platform is currently being submitted for inclusion, so
> I'd definitely hope to see this driver get merged too eventually.
> 
> IIRC, the last revision of the patch set had basically fixed the problem,
> except for a race that would still allow the napi poll function to exit
> with poll_complete() but a full queue of TX descriptors and no fallback
> to clean them up. There was also still an open question about whether or
> not the driver should use skb_orphan, but I may be misremembering that part.
>  

Hi Arnd:

what about use a state machine to check the tx queue and free the skb, just like:

diff --git a/drivers/net/ethernet/hisilicon/hip04_eth.c b/drivers/net/ethernet/hisilicon/hip04_eth.c
index 8593658..71faca8 100644
--- a/drivers/net/ethernet/hisilicon/hip04_eth.c
+++ b/drivers/net/ethernet/hisilicon/hip04_eth.c
@@ -396,9 +396,25 @@ static int hip04_mac_start_xmit(struct sk_buff *skb, struct net_device *ndev)
        stats->tx_packets++;
        priv->tx_count++;

+
+       queue_delayed_work(priv->wq, &priv->tx_queue, delay);
+
        return NETDEV_TX_OK;
 }

+static void hip04_tx_queue_monitor(struct work_struct *work)
+{
+       struct hip04_priv *priv = container_of(work, struct hip04_priv,
+                                              queue_work.work);
+       struct net_device *dev = priv->ndev;
+       hip04_tx_reclain(ndev, false);
+
+       if (TX_QUEUE_IS_EMPRY(ndev))
+               return;
+
+       queue_delayed_work(priv->wq, &priv->tx_queue, delay);
+}
+
 static int hip04_rx_poll(struct napi_struct *napi, int budget)
 {
        struct hip04_priv *priv = container_of(napi, struct hip04_priv, napi);
@@ -736,6 +752,8 @@ static int hip04_mac_probe(struct platform_device *pdev)
                goto alloc_fail;
        }

+       INIT_DELAYED_WORK(&priv->tx_queue, hip04_tx_queue_monitor);
+
        return 0;

what do you think of this solution?

Regards
Ding

>> Dave, what's your take here? Should we keep a driver from going upstream
>> just because the hardware is partly broken? I'd really prefer to have an
>> upstream driver on that SoC rather than some random (eventually even
>> more broken) downstream code.
> 
> We can certainly have a slow driver for this hardware, and I'd much
> prefer slow over broken. I'd guess that some of the performance impact
> of the missing interrupts can now be offset with the xmit_more	 logic.
> 
> 	Arnd
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