Re: [PATCH v2] usb: dwc3: gadget: Prevent irq storm when TH re-executes

Badhri Jagan Sridharan
2025-02-11T00:41:34Z

.

On Mon, Feb 10, 2025 at 4:22 PM Thinh Nguyen <Thinh.Nguyen@synopsys.com> wrote:
>
> On Sat, Feb 08, 2025, Badhri Jagan Sridharan wrote:
> > While commit d325a1de49d6 ("usb: dwc3: gadget: Prevent losing events in
> > event cache") makes sure that top half(TH) does not end up overwriting the
> > cached events before processing them when the TH gets invoked more than one
> > time, returning IRQ_HANDLED results in occasional irq storm where the TH
> > hogs the CPU. The irq storm can be prevented by clearing the flag before
> > event handler busy is cleared. Default enable interrupt moderation in all
> > versions which support them.
> >
> > ftrace event stub during dwc3 irq storm:
> > irq/504_dwc3-1111 ( 1111) [000] .... 70.000866: irq_handler_exit: irq=14 ret=handled
> > irq/504_dwc3-1111 ( 1111) [000] .... 70.000872: irq_handler_entry: irq=504 name=dwc3
> > irq/504_dwc3-1111 ( 1111) [000] .... 70.000874: irq_handler_exit: irq=504 ret=handled
> > irq/504_dwc3-1111 ( 1111) [000] .... 70.000881: irq_handler_entry: irq=504 name=dwc3
> > irq/504_dwc3-1111 ( 1111) [000] .... 70.000883: irq_handler_exit: irq=504 ret=handled
> > irq/504_dwc3-1111 ( 1111) [000] .... 70.000889: irq_handler_entry: irq=504 name=dwc3
> > irq/504_dwc3-1111 ( 1111) [000] .... 70.000892: irq_handler_exit: irq=504 ret=handled
> > irq/504_dwc3-1111 ( 1111) [000] .... 70.000898: irq_handler_entry: irq=504 name=dwc3
> > irq/504_dwc3-1111 ( 1111) [000] .... 70.000901: irq_handler_exit: irq=504 ret=handled
> > irq/504_dwc3-1111 ( 1111) [000] .... 70.000907: irq_handler_entry: irq=504 name=dwc3
> > irq/504_dwc3-1111 ( 1111) [000] .... 70.000909: irq_handler_exit: irq=504 ret=handled
> > irq/504_dwc3-1111 ( 1111) [000] .... 70.000915: irq_handler_entry: irq=504 name=dwc3
> > irq/504_dwc3-1111 ( 1111) [000] .... 70.000918: irq_handler_exit: irq=504 ret=handled
> > irq/504_dwc3-1111 ( 1111) [000] .... 70.000924: irq_handler_entry: irq=504 name=dwc3
> > irq/504_dwc3-1111 ( 1111) [000] .... 70.000927: irq_handler_exit: irq=504 ret=handled
> > irq/504_dwc3-1111 ( 1111) [000] .... 70.000933: irq_handler_entry: irq=504 name=dwc3
> > irq/504_dwc3-1111 ( 1111) [000] .... 70.000935: irq_handler_exit: irq=504 ret=handled
> > ....
> >
> > Cc: stable@kernel.org
> > Suggested-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
> > Fixes: d325a1de49d6 ("usb: dwc3: gadget: Prevent losing events in event cache")
> > Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
> > ---
> > drivers/usb/dwc3/core.c | 2 +-
> > drivers/usb/dwc3/gadget.c | 10 +++++++---
> > 2 files changed, 8 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> > index dfa1b5fe48dc..6df971ef7285 100644
> > --- a/drivers/usb/dwc3/core.c
> > +++ b/drivers/usb/dwc3/core.c
> > @@ -1835,7 +1835,7 @@ static void dwc3_get_properties(struct dwc3 *dwc)
> > dwc->tx_thr_num_pkt_prd = tx_thr_num_pkt_prd;
> > dwc->tx_max_burst_prd = tx_max_burst_prd;
> >
> > - dwc->imod_interval = 0;
> > + dwc->imod_interval = 1;
>
> Use dwc3_has_imod() to determine whether to set this. Otherwise we get
> a warning on setups that don't support imod.

Hi Thinh,

dwc3_check_params() which gets invoked after dwc3_get_properties() at
https://elixir.bootlin.com/linux/v6.14-rc1/source/drivers/usb/dwc3/core.c#L1851
seems to already call dwc3_has_imod(). Do you prefer me to add an
explicit check here as well ?

Thanks,
Badhri

>
> >
> > dwc->tx_fifo_resize_max_num = tx_fifo_resize_max_num;
> > }
> > diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> > index d27af65eb08a..fad115113d28 100644
> > --- a/drivers/usb/dwc3/gadget.c
> > +++ b/drivers/usb/dwc3/gadget.c
> > @@ -4467,14 +4467,18 @@ static irqreturn_t dwc3_process_event_buf(struct dwc3_event_buffer *evt)
> > dwc3_writel(dwc->regs, DWC3_GEVNTSIZ(0),
> > DWC3_GEVNTSIZ_SIZE(evt->length));
> >
> > + evt->flags &= ~DWC3_EVENT_PENDING;
> > + /*
> > + * Add an explicit write memory barrier to make sure that the update of
> > + * clearing DWC3_EVENT_PENDING is observed in dwc3_check_event_buf()
> > + */
> > + wmb();
> > +
> > if (dwc->imod_interval) {
> > dwc3_writel(dwc->regs, DWC3_GEVNTCOUNT(0), DWC3_GEVNTCOUNT_EHB);
> > dwc3_writel(dwc->regs, DWC3_DEV_IMOD(0), dwc->imod_interval);
> > }
> >
> > - /* Keep the clearing of DWC3_EVENT_PENDING at the end */
> > - evt->flags &= ~DWC3_EVENT_PENDING;
> > -
> > return ret;
> > }
> >
> >
> > base-commit: 9682c35ff6ecd76d9462d4749b8b413d3e8e605e
> > --
> > 2.48.1.502.g6dc24dfdaf-goog
> >
>
> The rest looks fine.
>
> Thanks,
> Thinh