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Message-ID: <20240831005046.5lndwdr7cfm3k3to@synopsys.com>
Date: Sat, 31 Aug 2024 00:50:55 +0000
From: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To: Selvarasu Ganesan <selvarasu.g@...sung.com>
CC: Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"jh0801.jung@...sung.com" <jh0801.jung@...sung.com>,
"dh10.jung@...sung.com" <dh10.jung@...sung.com>,
"naushad@...sung.com" <naushad@...sung.com>,
"akash.m5@...sung.com" <akash.m5@...sung.com>,
"rc93.raju@...sung.com" <rc93.raju@...sung.com>,
"taehyun.cho@...sung.com" <taehyun.cho@...sung.com>,
"hongpooh.kim@...sung.com" <hongpooh.kim@...sung.com>,
"eomji.oh@...sung.com" <eomji.oh@...sung.com>,
"shijie.cai@...sung.com" <shijie.cai@...sung.com>
Subject: Re: [PATCH] usb: dwc3: Potential fix of possible dwc3 interrupt storm
Hi Selvarasu,
On Fri, Aug 30, 2024, Selvarasu Ganesan wrote:
>
> On 8/10/2024 5:12 AM, Thinh Nguyen wrote:
> > On Thu, Aug 08, 2024, Selvarasu Ganesan wrote:
> >> On 8/8/2024 6:45 AM, Thinh Nguyen wrote:
> >>> On Wed, Aug 07, 2024, Selvarasu Ganesan wrote:
> >>>> On 8/7/2024 6:08 AM, Thinh Nguyen wrote:
> >>>>> On Fri, Jul 19, 2024, Selvarasu Ganesan wrote:
> >>>>>> In certain scenarios, there is a chance that the CPU may not be
> >>>>>> scheduled the bottom half of dwc3 interrupt. This is because the CPU
> >>>>>> may hang up where any work queue lockup has happened for the same CPU
> >>>>>> that is trying to schedule the dwc3 thread interrupt. In this scenario,
> >>>>>> the USB can enter runtime suspend as the bus may idle for a longer time
> >>>>>> , or user can reconnect the USB cable. Then, the dwc3 event interrupt
> >>>>>> can be enabled when runtime resume is happening with regardless of the
> >>>>>> previous event status. This can lead to a dwc3 IRQ storm due to the
> >>>>>> return from the interrupt handler by checking only the evt->flags as
> >>>>>> DWC3_EVENT_PENDING, where the same flag was set as DWC3_EVENT_PENDING
> >>>>>> in previous work queue lockup.
> >>>>>> Let's consider the following sequences in this scenario,
> >>>>>>
> >>>>>> Call trace of dwc3 IRQ after workqueue lockup scenario
> >>>>>> ======================================================
> >>>>>> IRQ #1:
> >>>>>> ->dwc3_interrupt()
> >>>>>> ->dwc3_check_event_buf()
> >>>>>> ->if (evt->flags & DWC3_EVENT_PENDING)
> >>>>>> return IRQ_HANDLED;
> >>>>>> ->evt->flags |= DWC3_EVENT_PENDING;
> >>>>>> ->/* Disable interrupt by setting DWC3_GEVNTSIZ_INTMASK in
> >>>>>> DWC3_GEVNTSIZ
> >>>>>> ->return IRQ_WAKE_THREAD; // No workqueue scheduled for dwc3
> >>>>>> thread_fu due to workqueue lockup
> >>>>>> even after return IRQ_WAKE_THREAD
> >>>>>> from top-half.
> >>>>>>
> >>>>>> Thread #2:
> >>>>>> ->dwc3_runtime_resume()
> >>>>>> ->dwc3_resume_common()
> >>>>>> ->dwc3_gadget_resume()
> >>>>>> ->dwc3_gadget_soft_connect()
> >>>>>> ->dwc3_event_buffers_setup()
> >>>>>> ->/*Enable interrupt by clearing DWC3_GEVNTSIZ_INTMASK in
> >>>>>> DWC3_GEVNTSIZ*/
> >>>>>>
> >>>>>> Start IRQ Storming after enable dwc3 event in resume path
> >>>>>> =========================================================
> >>>>>> CPU0: IRQ
> >>>>>> dwc3_interrupt()
> >>>>>> dwc3_check_event_buf()
> >>>>>> if (evt->flags & DWC3_EVENT_PENDING)
> >>>>>> return IRQ_HANDLED;
> >>>>>>
> >>>>>> CPU0: IRQ
> >>>>>> dwc3_interrupt()
> >>>>>> dwc3_check_event_buf()
> >>>>>> if (evt->flags & DWC3_EVENT_PENDING)
> >>>>>> return IRQ_HANDLED;
> >>>>>> ..
> >>>>>> ..
> >>>>>>
> >>>>>> To fix this issue by avoiding enabling of the dwc3 event interrupt in
> >>>>>> the runtime resume path if dwc3 event processing is in progress.
> >>>>>>
> >>>>>> Signed-off-by: Selvarasu Ganesan <selvarasu.g@...sung.com>
> >>>>>> ---
> >>>>>> drivers/usb/dwc3/core.c | 8 ++++++--
> >>>>>> 1 file changed, 6 insertions(+), 2 deletions(-)
> >>>>>>
> >>>>>> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> >>>>>> index cb82557678dd..610792a70805 100644
> >>>>>> --- a/drivers/usb/dwc3/core.c
> >>>>>> +++ b/drivers/usb/dwc3/core.c
> >>>>>> @@ -549,8 +549,12 @@ int dwc3_event_buffers_setup(struct dwc3 *dwc)
> >>>>>> lower_32_bits(evt->dma));
> >>>>>> dwc3_writel(dwc->regs, DWC3_GEVNTADRHI(0),
> >>>>>> upper_32_bits(evt->dma));
> >>>>>> - dwc3_writel(dwc->regs, DWC3_GEVNTSIZ(0),
> >>>>>> - DWC3_GEVNTSIZ_SIZE(evt->length));
> >>>>>> +
> >>>>>> + /* Skip enable dwc3 event interrupt if event is processing in middle */
> >>>>>> + if (!(evt->flags & DWC3_EVENT_PENDING))
> >>>>>> + dwc3_writel(dwc->regs, DWC3_GEVNTSIZ(0),
> >>>>>> + DWC3_GEVNTSIZ_SIZE(evt->length));
> >>>>>> +
> >>>>>> dwc3_writel(dwc->regs, DWC3_GEVNTCOUNT(0), 0);
> >>>>>>
> >>>>>> return 0;
> >>>>>> --
> >>>>>> 2.17.1
> >>>>>>
> >>>>> We're not waking up from a hibernation. So after a soft-reset and
> >>>>> resume, the events that weren't processed are stale. They should be
> >>>>> processed prior to entering suspend or be discarded before resume.
> >>>>>
> >>>>> The synchronize_irq() during suspend() was not sufficient to prevent
> >>>>> this? What are we missing here.
> >>>>>
> >>>>> Thanks,
> >>>>> Thinh
> >>>> I don’t think the triggering of interrupt would not be stopped even if
> >>>> do soft reset. It's because of event count is may be valid .
> >>> Ok. I think I see what you're referring to when you say "event is
> >>> processing in the middle" now.
> >>>
> >>> What you want to check is probably this in dwc3_event_buffers_setup().
> >>> Please confirm:
> >>>
> >>> if (dwc->pending_events)
> >>> dwc3_writel(dwc->regs, DWC3_GEVNTSIZ(0),
> >>> DWC3_GEVNTSIZ_INTMASK | DWC3_GEVNTSIZ_SIZE(evt->length));
> >>> else
> >>> dwc3_writel(dwc->regs, DWC3_GEVNTSIZ(0), DWC3_GEVNTSIZ_SIZE(evt->length));
> >> Yes, we are expecting the same. But, we must verify the status of
> >> evt->flags, which will indicate whether the event is currently
> >> processing in middle or not. The below code is for the reference.
> >>
> >> if (!(evt->flags & DWC3_EVENT_PENDING))
> >> dwc3_writel(dwc->regs, DWC3_GEVNTSIZ(0),
> >> DWC3_GEVNTSIZ_SIZE(evt->length));
> >> else
> >> dwc3_writel(dwc->regs, DWC3_GEVNTSIZ(0),
> >> DWC3_GEVNTSIZ_INTMASK | DWC3_GEVNTSIZ_SIZE(evt->length));
> > So, this happens while pending_events is set right? I need to review
> > this runtime suspend flow next week. Something doesn't look right. When
> > there's a suspend/resume runtime or not, there's a soft disconnect. We
> > shouldn't be processing any event prior to going into suspend. Also, we
> > shouldn't be doing soft-disconnect while connected and in operation
> > unless we specifically tell it to.
> HI Thinh,
>
> Would you be able to review this runtime suspend flow?
>
> From our end, after conducting multiple regression tests, we have
> determined that the resetting of "evt->flags" are sufficient when
> attempting to enable event IRQ masks instead of enable event IRQ mask
> based on pending event flags. There is a possibility that reconnecting
> USB with the host PC may cause event interrupts to be missed by the CPU
> if disable event IRQ mask. So, The fix should be as follow. Could you
> please review this once from your end?
>
> diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> index ccc3895dbd7f..3b2441608e9e 100644
> --- a/drivers/usb/dwc3/core.c
> +++ b/drivers/usb/dwc3/core.c
> @@ -554,6 +554,15 @@ int dwc3_event_buffers_setup(struct dwc3 *dwc)
> lower_32_bits(evt->dma));
> dwc3_writel(dwc->regs, DWC3_GEVNTADRHI(0),
> upper_32_bits(evt->dma));
> +
> + /*
> + * The DWC3_EVENT_PENDING flag is cleared if it has
> + * already been set when enabling the event IRQ mask
> + * to prevent possibly of an IRQ storm.
> + */
> + if (evt->flags & DWC3_EVENT_PENDING)
> + evt->flags &= ~DWC3_EVENT_PENDING;
> +
> dwc3_writel(dwc->regs, DWC3_GEVNTSIZ(0),
> DWC3_GEVNTSIZ_SIZE(evt->length));
> dwc3_writel(dwc->regs, DWC3_GEVNTCOUNT(0), 0);
>
Sorry for the delay response.
In addition to that, please rework and rename
dwc3_gadget_process_pending_event(). We're not supposed to handle any
left-over event. So remove the manual calls to the interrupt handlers
there.
On runtime suspend, the device is soft disconnected. So any interrupt
assertion to notify a new connection must be a custom configuration of
your platform. No event should be generated while the run_stop bit is
cleared.
On runtime resume, we will initiate soft-reset and soft-connect to
restore the run_stop bit. A new connection event will be generated then.
Thanks,
Thinh
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