Re: [PATCH v1] usb: dwc3: gadget: Prevent irq storm when TH re-executes

[Thinh Nguyen <Thinh.Nguyen@synopsys.com>]

On Fri, Jan 24, 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 if
> IRQ_WAKE_THREAD is returned.
> 
> 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
> Fixes: d325a1de49d6 ("usb: dwc3: gadget: Prevent losing events in event cache")

I don't think this should be Cc to stable, at least not the way it is
right now.

> Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
> ---
>  drivers/usb/dwc3/gadget.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> index d27af65eb08a..376ab75adc4e 100644
> --- a/drivers/usb/dwc3/gadget.c
> +++ b/drivers/usb/dwc3/gadget.c
> @@ -4519,7 +4519,7 @@ static irqreturn_t dwc3_check_event_buf(struct dwc3_event_buffer *evt)
>  	 * losing events.
>  	 */
>  	if (evt->flags & DWC3_EVENT_PENDING)
> -		return IRQ_HANDLED;
> +		return IRQ_WAKE_THREAD;

This looks like a workaround to the issue we have. Have you tried to
enable imod instead? It's the feature to help avoid these kind of issue.

Thanks,
Thinh

>  
>  	count = dwc3_readl(dwc->regs, DWC3_GEVNTCOUNT(0));
>  	count &= DWC3_GEVNTCOUNT_MASK;
> 
> base-commit: 70cd0576aa39c55aabd227851cba0c601e811fb6
> -- 
> 2.48.1.262.g85cc9f2d1e-goog
>