Re: [PATCH] usb: dwc3: Clear DWC3_EVENT_PENDING when count is 0

From: Linyu Yuan <quic_linyyuan@quicinc.com>
To: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
Cc: 정재훈 <jh0801.jung@samsung.com>,
	"'Felipe Balbi'" <balbi@kernel.org>,
	"'Greg Kroah-Hartman'" <gregkh@linuxfoundation.org>,
	"'open list:USB XHCI DRIVER'" <linux-usb@vger.kernel.org>,
	"'open list'" <linux-kernel@vger.kernel.org>,
	"'Seungchull Suh'" <sc.suh@samsung.com>,
	"'Daehwan Jung'" <dh10.jung@samsung.com>
Subject: Re: [PATCH] usb: dwc3: Clear DWC3_EVENT_PENDING when count is 0
Date: Tue, 10 Jan 2023 09:56:14 +0800	[thread overview]
Message-ID: <e7217471-5b08-eee6-fba8-06e879118d77@quicinc.com> (raw)
In-Reply-To: <20230109182813.sle5h34wdgglnlph@synopsys.com>

On 1/10/2023 2:28 AM, Thinh Nguyen wrote:
> On Fri, Jan 06, 2023, Linyu Yuan wrote:
>> On 1/5/2023 5:54 PM, 정재훈 wrote:
>>>> -----Original Message-----
>>>> From: Linyu Yuan [mailto:quic_linyyuan@quicinc.com]
>>>> Sent: Thursday, January 5, 2023 12:35 PM
>>>> To: JaeHun Jung; Felipe Balbi; Greg Kroah-Hartman; Thinh Nguyen
>>>> Cc: open list:USB XHCI DRIVER; open list; Seungchull Suh; Daehwan Jung
>>>> Subject: Re: [PATCH] usb: dwc3: Clear DWC3_EVENT_PENDING when count is 0
>>>>
>>>>
>>>> On 1/5/2023 11:29 AM, Linyu Yuan wrote:
>>>>> On 1/2/2023 1:08 PM, JaeHun Jung wrote:
>>>>>> Sometimes very rarely, The count is 0 and the DWC3 flag is set has
>>>>>> status.
>>>>>> It must not have these status. Because, It can make happen interrupt
>>>>>> storming status.
>>>>> could you help explain without clear the flag, how interrupt storming
>>>>> happen ?
>>>>>
>>>>> as your change didn't touch any hardware register, i don't know how it
>>>>> fix storming.
>>>>>
>>> H/W interrupts are still occur on IP.
>> I guess we should fix it from IP layer.
>>
> How are you certain the problem is from IP layer?

I think all IRQ is from DWC3 controller IP. if it is not IP layer, could 
you share how to prevent from SW layer ?

seem IRQ can happen when event count is zero ,  why this can happen ? 
does it mean event count register is not trust ?

>
>> but when checking DWC3_EVENT_PENDING flag, it will auto clear in dwc3 thread
>> irq handler.
>>
>> there is one possible root cause is it cleared only after irq enabled in
>> dwc3_process_event_buf(),
>>
>> we should move unmask irq operation at end of this function.
>>
> This interrupt storm can happen because we clear the evt->flags _after_
> we unmask the interrupt. This was done to prevent false interrupt from
> delay interrupt deassertion, which can be a problem for legacy pci
> interrupt.
thanks for explain, i didn't know that.
>
> see 7441b273388b ("usb: dwc3: gadget: Fix event pending check")
>
> The change JaeHun Jung did should be fine.
agree.
> BR,
> Thinh