Re: [PATCH] HID: multitouch: add support for Type Cover Pro 3

[Benjamin Tissoires <benjamin.tissoires@redhat.com>]

Hi,

On Jun 25 2016 or thereabouts, Dennis Chen wrote:
> On Fri, 2016-06-24 at 09:14 +0200, Benjamin Tissoires wrote:
> > Looks like the same issue Andy is seeing on the Surface Book. So I
> > think my patch must have a bug where it resets the quirks set by
> > usbhid. And this is why we are screwed here.
> > 
> 
> Yes, I think that's likely. There doesn't seem to be an issue most of
> the time, so it's not a huge deal. 

I spent a good amount of time trying to figure out where the bug was,
and I couldn't reproduce it either with uhid or even with usb_gadget.
Even KASan doesn't gives any wrong memory access, and I can't understand
why you get this faulty behavior.

So I must say, I am puzzled on why you end up calling
usbhid_init_reports() while the quirk HID_QUIRK_NO_INIT_REPORTS should
be in place.
Would you mind adding some printk() in hid-multitouch to dump the value
of hdev->quirks before and after calling hid_hw_start() in mt_probe()?

Also, ideally, if you could add a dump_stack() in
drivers/hid/usbhid/hid-core.c, right before leaving
usbhid_init_reports(), that would be awesome.

I would have prefer being able to understand myself what is going on,
but it looks like there is something different happening when I do not
have the device.

> 
> > Regarding your disconnect issue, what happens I think is that you
> > disconnect it before the timeout of usb_submit_urb(), and so the usb
> > layer is stuck trying to access the device and can't access the newly
> > plugged one. If you wait enough (initial timeout + new timeout -> 20
> > secs), then the device behaves properly again.
> > 
> 
> That is the behavior I have noticed. Is there any potential fix?
> 

The fix is to not fetch the buggy features that timeout. For that, we
usually set the flag HID_QUIRK_NO_INIT_REPORTS, which prevents it. But
in your case, the code says that the flag is set, while the code is
still called :(

Thanks,
Benjamin


--
To unsubscribe from this list: send the line "unsubscribe linux-input" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html