linux-kernel - Re: [PATCH] usb: dwc3: Clear DWC3_EVENT

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Date:   Mon, 9 Jan 2023 18:28:18 +0000
From:   Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To:     Linyu Yuan <quic_linyyuan@...cinc.com>
CC:     정재훈 <jh0801.jung@...sung.com>,
        'Felipe Balbi' <balbi@...nel.org>,
        'Greg Kroah-Hartman' <gregkh@...uxfoundation.org>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        "'open list:USB XHCI DRIVER'" <linux-usb@...r.kernel.org>,
        'open list' <linux-kernel@...r.kernel.org>,
        'Seungchull Suh' <sc.suh@...sung.com>,
        'Daehwan Jung' <dh10.jung@...sung.com>
Subject: Re: [PATCH] usb: dwc3: Clear DWC3_EVENT_PENDING when count is 0

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@...cinc.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?

> 
> 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.

see 7441b273388b ("usb: dwc3: gadget: Fix event pending check")

The change JaeHun Jung did should be fine.

BR,
Thinh