Re: [RFC][PATCH] usb: typec: tcpci_rt1711h: Try to avoid screaming irq causing boot hangs

[Jun Li]

Hi,
John Stultz <john.stultz@xxxxxxxxxx> ä2020å6æ2æåä äå4:39åéï
>
> On Sat, May 30, 2020 at 3:30 AM Jun Li <lijun.kernel@xxxxxxxxx> wrote:
> >
> > Hi John,
> >
> > John Stultz <john.stultz@xxxxxxxxxx> ä2020å5æ30æåå äå12:02åéï
> > >
> > > I've recently (since 5.7-rc1) started noticing very rare hangs
> > > pretty early in bootup on my HiKey960 board.
> > >
> > > They have been particularly difficult to debug, as the system
> > > seems to not respond at all to sysrq- commands. However, the
> > > system is alive as I'll occaionally see firmware loading timeout
> > > errors after awhile. Adding changes like initcall_debug and
> > > lockdep weren't informative, as it tended to cause the problem
> > > to hide.
> > >
> > > I finally tried to dig in a bit more on this today, and noticed
> > > that the last dmesg output before the hang was usually:
> > >   "random: crng init done"
> > >
> > > So I dumped the stack at that point, and saw it was being called
> > > from the pl061 gpio irq, and the hang always occurred when the
> > > crng init finished on cpu 0. Instrumenting that more I could see
> > > that when the issue triggered, we were getting a stream of irqs.
> > >
> > > Chasing further, I found the screaming irq was for the rt1711h,
> > > and narrowed down that we were hitting the !chip->tcpci check
> > > which immediately returns IRQ_HANDLED, but does not stop the
> > > irq from triggering immediately afterwards.
> > >
> > > This patch slightly reworks the logic, so if we hit the irq
> > > before the chip->tcpci has been assigned, we still read and
> > > write the alert register, but just skip calling tcpci_irq().
> > >
> > > With this change, I haven't managed to trip over the problem
> > > (though it hasn't been super long - but I did confirm I hit
> > > the error case and it didn't hang the system).
> > >
> > > I still have some concern that I don't know why this cropped
> > > up since 5.7-rc, as there haven't been any changes to the
> > > driver since 5.4 (or before). It may just be the initialization
> > > timing has changed due to something else, and its just exposed
> > > this issue? I'm not sure, and that's not super re-assuring.
> > >
> > > Anyway, I'd love to hear your thoughts if this looks like a sane
> > > fix or not.
> >
> > I think a better solution may be move the irq request after port register,
> > we should fire the irq after everything is setup.
> > does below change works for you?
>
> Unfortunately the patch didn't seem to apply, but I recreated it by
> hand. I agree this looks like it should address the issue and I've not
> managed to trigger the problem in my (admittedly somewhat brief)
> attempts at testing.
>
> Thanks for sending it out. Do you want to submit the patch and I'll
> provide a Tested-by tag, or would it help for me to submit your
> suggested change?

OK, I will send out a patch against Greg's tree.

Li Jun
>
> thanks
> -john