Re: [PATCH v2 2/2] Revert "usb: dwc3: Don't switch OTG -> peripheral if extcon is present"

[Andrey Smirnov]

On Mon, Oct 10, 2022 at 12:13 AM Andy Shevchenko
<andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:
>
> On Sun, Oct 09, 2022 at 10:02:26PM -0700, Andrey Smirnov wrote:
> > On Fri, Oct 7, 2022 at 6:07 AM Ferry Toth <fntoth@xxxxxxxxx> wrote:
>
> Thank you for the testing on your side!
>
> ...
>
> > OK, Ferry, I think I'm going to need clarification on specifics on
> > your test setup. Can you share your kernel config, maybe your
> > "/proc/config.gz", somewhere? When you say you are running vanilla
> > Linux, do you mean it or do you mean vanilla tree + some patch delta?
> >
> > The reason I'm asking is because I'm having a hard time reproducing
> > the problem on my end. In fact, when I build v6.0
> > (4fe89d07dcc2804c8b562f6c7896a45643d34b2f) and then do a
> >
> > git revert 8bd6b8c4b100 0f0101719138 (original revert proposed by Andy)
> >
> > I get an infinite loop of reprobing that looks something like (some
> > debug tracing, function name + line number, included):
>
> Yes, this is (one of) known drawback(s) of deferred probe hack. I think
> the kernel that Ferry runs has a patch that basically reverts one from
> 2014 [1] and allows to have extcon as a module. (1)
>
> [1]: 58b116bce136 ("drivercore: deferral race condition fix")
>
> > which renders the system completely unusable, but USB host is
> > definitely going to be broken too. Now, ironically, with my patch
> > in-place, an attempt to probe extcon that ends up deferring the probe
> > happens before the ULPI driver failure (which wasn't failing driver
> > probe prior to https://lore.kernel.org/all/20220213130524.18748-7-hdegoede@xxxxxxxxxx/),
> > there no "driver binding" event that re-triggers deferred probe
> > causing the loop, so the system progresses to a point where extcon is
> > available and dwc3 driver eventually loads.
> >
> > After that, and I don't know if I'm doing the same test, USB host
> > seems to work as expected. lsusb works, my USB stick enumerates as
> > expected. Switching the USB mux to micro-USB and back shuts the host
> > functionality down and brings it up as expected. Now I didn't try to
> > load any gadgets to make sure USB gadget works 100%, but since you
> > were saying it was USB host that was broken, I wasn't concerned with
> > that. Am I doing the right test?
>
> Hmm... What you described above sounds more like a yet another attempt to
> workaround (1). _If_ this is the case, we probably can discuss how to fix
> it in generic way (somewhere in dd.c, rather than in the certain driver).
>

No, I'm not describing an attempt to fix anything. Just how vanilla
v6.0 (where my patch is not reverted) works and where my patch, fixing
a logical problem in which extcon was requested too late causing a
forced OTG -> "gadget only" switch, also changed the ordering enough
to accidentally avoid the loop.

> That said, the real test case should be performed on top of clean kernel
> before judging if it's good or bad.
>

Given your level of involvemnt with this particular platform and you
being the author of
https://github.com/edison-fw/meta-intel-edison/blob/master/meta-intel-edison-bsp/recipes-kernel/linux/files/0043b-TODO-driver-core-Break-infinite-loop-when-deferred-p.patch
I assumed/expected you to double check this before sending this revert
out. Please do so next time.