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

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Date:   Thu, 2 Feb 2023 13:00:26 +0800
From:   Linyu Yuan <quic_linyyuan@...cinc.com>
To:     Thinh Nguyen <Thinh.Nguyen@...opsys.com>
CC:     정재훈 <jh0801.jung@...sung.com>,
        'Felipe Balbi' <balbi@...nel.org>,
        'Greg Kroah-Hartman' <gregkh@...uxfoundation.org>,
        "'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 2/2/2023 2:57 AM, Thinh Nguyen wrote:
> On Tue, Jan 31, 2023, Linyu Yuan wrote:
>> hi Thinh,
>>
>>
>> regarding your suggestion, assume it is not PCIe type,  still have one
>> question,
>>
>>
>> -       if (evt->flags & DWC3_EVENT_PENDING)
>> +       if (evt->flags & DWC3_EVENT_PENDING) {
>> +               if (!evt->count) {
>> +                       u32 reg = dwc3_readl(dwc->regs, DWC3_GEVNTSIZ(0));
>> +
>> +                       if (!(reg & DWC3_GEVNTSIZ_INTMASK))
>> +                               evt->flags &= ~DWC3_EVENT_PENDING;
>>
>> do we need to return IRQ_WAKE_THREAD  ?
> No, if evt->count is 0, but GEVNTCOUNT is > 0, the controller will
> generate interrupt. The evt->count will be updated and the events will
> be handled on the next interrupt.


when will next interrupt happen ?

as when enter here, i guess GEVENTCOUNT is already > 0, but we didn't 
read it.


>
>> +               }
>>                  return IRQ_HANDLED;
>>
>> as here return IRQ HANDLED, how can we make sure a new IRQ will be handled
>> after previous IRQ thread clean PENDING flag ?
> If evt->count > 0, that means the bottom half is still running. So,
> leave it be. If evt->count == 0, then the cached events are processed,
> we're safe to clear the PENDING flag. New interrupt will be generated if
> GEVNTCOUNT is > 0.
>
>> +       }
>>
>>
>> also for non-PCIe controller, consider IRQ mask register working correctly,
>>
>> consider a case IRQ happen before IRQ thread exit,  here just return
>> IRQ_HANDLED.
>>
>> once IRQ thread exit, it will clean PENDING flag, so next IRQ event will run
>> normally.
>>
>> if 정재훈 saw PENDING flag is not cleared, does it mean IRQ thread have no
>> chance to exit ?
> The PENDING flag should be cleared eventually when the bottom half
> completes. I don't expect the interrupt storm to block the IRQ thread
> forever, but I can't guarantee the device behavor. 정재훈 can confirm.
> This change should resolve the interrupt storm.
>
> BR,
> Thinh