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

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

On Wed, Feb 12, 2025, Badhri Jagan Sridharan wrote:
> On Mon, Feb 10, 2025 at 4:55 PM Thinh Nguyen <Thinh.Nguyen@synopsys.com> wrote:
> >
> > 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.
> 
> Hi Thinh,
> 
> Looks like adding dwc3_has_imod() in dwc3_get_properties() would not
> be possible as the dwc->revision gets filled in much later at
> dwc3_core_is_valid():
> https://urldefense.com/v3/__https://elixir.bootlin.com/linux/v6.14-rc2/source/drivers/usb/dwc3/core.c*L2218__;Iw!!A4F2R9G_pg!d67RghVyoDYTtMqlnAcNgHywoW0ZfJnYX1NSjokyqaBnPrdiF4w0FlFgTGDEVcSZeUHfpBGIgQtx_UAa1t0$ ,
> also, the core is still not brought out of reset yet. Would it be
> reasonable to initialize dwc->imod_interval to 1 in
> dwc3_check_params() like below ?
> 
> +++ b/drivers/usb/dwc3/core.c
> @@ -1835,8 +1835,6 @@ 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 = 1;
> -
>         dwc->tx_fifo_resize_max_num = tx_fifo_resize_max_num;
>  }
> 
> @@ -1858,6 +1856,8 @@ static void dwc3_check_params(struct dwc3 *dwc)
>         if (dwc->imod_interval && !dwc3_has_imod(dwc)) {
>                 dev_warn(dwc->dev, "Interrupt moderation not supported\n");
>                 dwc->imod_interval = 0;
> +       } else if (!dwc->imod_interval && dwc3_has_imod(dwc)) {
> +               dwc->imod_interval = 1;
>         }
> 

Can you consolidate all the settings of IMOD to the below:

diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
index 423866b2ffaa..a485fef82301 100644
--- a/drivers/usb/dwc3/core.c
+++ b/drivers/usb/dwc3/core.c
@@ -2021,21 +2021,19 @@ static void dwc3_check_params(struct dwc3 *dwc)
        unsigned int hwparam_gen =
                DWC3_GHWPARAMS3_SSPHY_IFC(dwc->hwparams.hwparams3);
 
-       /* Check for proper value of imod_interval */
-       if (dwc->imod_interval && !dwc3_has_imod(dwc)) {
-               dev_warn(dwc->dev, "Interrupt moderation not supported\n");
-               dwc->imod_interval = 0;
-       }
-
        /*
+        * Enable IMOD for all supporting controllers.
+        *
+        * Particularly, DWC_usb3 v3.00a must enable this feature for
+        * the following reason:
+        *
         * Workaround for STAR 9000961433 which affects only version
         * 3.00a of the DWC_usb3 core. This prevents the controller
         * interrupt from being masked while handling events. IMOD
         * allows us to work around this issue. Enable it for the
         * affected version.
         */
-       if (!dwc->imod_interval &&
-           DWC3_VER_IS(DWC3, 300A))
+       if (dwc3_has_imod((dwc)))
                dwc->imod_interval = 1;


Thanks,
Thinh