netdev - Re: [PATCH net 6/7] net: hns3: fix VF reset fail issue

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Message-ID: <97732cc0a75c0be3f2354075085e7fa6d78e82bb.camel@redhat.com>
Date: Thu, 02 Nov 2023 17:24:14 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Jijie Shao <shaojijie@...wei.com>, yisen.zhuang@...wei.com, 
 salil.mehta@...wei.com, davem@...emloft.net, edumazet@...gle.com,
 kuba@...nel.org
Cc: shenjian15@...wei.com, wangjie125@...wei.com, liuyonglong@...wei.com, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net 6/7] net: hns3: fix VF reset fail issue

On Thu, 2023-11-02 at 20:16 +0800, Jijie Shao wrote:
> on 2023/11/2 18:45, Paolo Abeni wrote:
> > On Sat, 2023-10-28 at 10:59 +0800, Jijie Shao wrote:
> > >   
> > > -static void hclgevf_clear_event_cause(struct hclgevf_dev *hdev, u32 regclr)
> > > +static void hclgevf_clear_event_cause(struct hclgevf_dev *hdev, u32 regclr,
> > > +				      bool need_dalay)
> > >   {
> > > +#define HCLGEVF_RESET_DELAY		5
> > > +
> > > +	if (need_dalay)
> > > +		mdelay(HCLGEVF_RESET_DELAY);
> > 5ms delay in an interrupt handler is quite a lot. What about scheduling
> > a timer from the IH to clear the register when such delay is needed?
> > 
> > Thanks!
> > 
> > Paolo
> 
> Using timer in this case will complicate the code and make maintenance difficult.

Why? 

Would something alike the following be ok? (plus reset_timer
initialization at vf creation and cleanup at vf removal time):

---
diff --git a/drivers/net/ethernet/hisilicon/hns3/hns3vf/hclgevf_main.c b/drivers/net/ethernet/hisilicon/hns3/hns3vf/hclgevf_main.c
index a4d68fb216fb..626bc67065fc 100644
--- a/drivers/net/ethernet/hisilicon/hns3/hns3vf/hclgevf_main.c
+++ b/drivers/net/ethernet/hisilicon/hns3/hns3vf/hclgevf_main.c
@@ -1974,6 +1974,14 @@ static enum hclgevf_evt_cause hclgevf_check_evt_cause(struct hclgevf_dev *hdev,
 	return HCLGEVF_VECTOR0_EVENT_OTHER;
 }
 
+static void hclgevf_reset_timer(struct timer_list *t)
+{
+	struct hclgevf_dev *hdev = from_timer(hclgevf_dev, t, reset_timer);
+
+	hclgevf_clear_event_cause(hdev, HCLGEVF_VECTOR0_EVENT_RST);
+	hclgevf_reset_task_schedule(hdev);
+}
+
 static irqreturn_t hclgevf_misc_irq_handle(int irq, void *data)
 {
 	enum hclgevf_evt_cause event_cause;
@@ -1982,13 +1990,13 @@ static irqreturn_t hclgevf_misc_irq_handle(int irq, void *data)
 
 	hclgevf_enable_vector(&hdev->misc_vector, false);
 	event_cause = hclgevf_check_evt_cause(hdev, &clearval);
+	if (event_cause == HCLGEVF_VECTOR0_EVENT_RST)
+		mod_timer(hdev->reset_timer, jiffies + msecs_to_jiffies(5));
+
 	if (event_cause != HCLGEVF_VECTOR0_EVENT_OTHER)
 		hclgevf_clear_event_cause(hdev, clearval);
 
 	switch (event_cause) {
-	case HCLGEVF_VECTOR0_EVENT_RST:
-		hclgevf_reset_task_schedule(hdev);
-		break;
 	case HCLGEVF_VECTOR0_EVENT_MBX:
 		hclgevf_mbx_handler(hdev);
 		break;
---

> We consider reducing the delay time by polling. For example,
> the code cycles every 50 us to check whether the write register takes effect.
> If yes, the function returns immediately. or the code cycles until 5 ms.
> 
> Is this method appropriate?

IMHO such solution will not remove the problem. How frequent is
expected to be the irq generating such delay?

Thanks

Paolo