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

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

On Mon, Feb 10, 2025, Badhri Jagan Sridharan wrote:
> .
> 
> 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://urldefense.com/v3/__https://elixir.bootlin.com/linux/v6.14-rc1/source/drivers/usb/dwc3/core.c*L1851__;Iw!!A4F2R9G_pg!Zar83WUe4sM-EF4c2wR2-vWBJHgYOCWEc1ijhOsWQHiXtzCF0d_t2gckS0YJUv4lAZgGZl2C-oSp1QMIx28$ 
> seems to already call dwc3_has_imod(). Do you prefer me to add an
> explicit check here as well ?
> 

Yes. I don't want to see dev_warn print when there shouldn't be any for
setup that don't support imod.

BR,
Thinh