Message-ID: <20160829102402.GA3736@b29397-desktop>
Date:   Mon, 29 Aug 2016 18:24:03 +0800
From:   Peter Chen <hzpeterchen@...il.com>
To:     Clemens Gruber <clemens.gruber@...ruber.com>
Cc:     linux-usb@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: chipidea: udc: kernel panic in isr_setup_status_phase

On Sun, Aug 28, 2016 at 08:15:02PM +0200, Clemens Gruber wrote:
> On Sat, Aug 27, 2016 at 01:21:52AM +0800, Peter Chen wrote:
> > The gadget triggers UI interrupt due to host sends packet.
> > 
> > I really can't understand that, why host does not send bus reset
> > before sending packet (eg, GET_DESCRIPTOR)? It violates USB spec.
> > 
> > Are you sure the first interrupt is UI when the vbus from off to on?
> 
> Yes, if the error is present, the first interrupt is intr=0x1 (USBi_UI)
> and then the NULL pointer dereference would occur.
> (Also: Checking for ci->status == NULL and avoiding the dereference does
> not make the gadget work. It just avoids the kernel panic.)
> 
> But I also observed a situation where the first interrupt is intr=0x100
> (USBi_SLI) followed by 0x40 (USBi_URI), 0x4 (USBi_PCI) and three times
> 0x1 (USBi_UI).
> After this "g_ether gadget: suspend" appears and the sequence repeats,
> starting again with intr=0x100, followed by 0x40, ... until three times
> 0x1 and the g_ether gadget: suspend message.
> On the host, every 500ms a new message with incrementing device number
> appears:
> usb 1-4: new high-speed USB device number 41 using xhci_hcd
> usb 1-4: new high-speed USB device number 42 using xhci_hcd
> ...
> 
> In the case where everything works, it looks like this:
> intr=0x100 (USBi_SLI)
> intr=0x40 (USBi_URI)
> intr=0x4 (USBi_PCI)
> intr=0x1 (USBi_UI)
> intr=0x1 (USBi_UI)
> ci_hdrc ci_hdrc.0: freeing queued_request
> intr=0x41 (USBi_URI + USBi_UI)
> intr=0x4 (USBi_PCI)
> intr=0x1 (USBi_UI) <-- appears 17 times
> g_ether gadget: high-speed config #1: CDC Ethernet (EEM)
> intr=0x1 (USBi_UI) <-- appears 5 times
> IPv6: ADDRCONF(NETDEV_CHANGE): usb0: link becomes ready
> 
> --
> 
> Do you think this could be a hardware problem? We used the same method
> as in the MCIMX6Q-SDB schematics (SPF-27516_C5.pdf) to avoid any current
> flow through OTG VBUS to the inside when the board is powered off but a
> host PC is still connected via OTG.
> So we not just pass the VBUS signal through, there are two MOSFETs,
> which prevent that (if the internal 3.3V is low).
> Mostly the same logic as in said document on page 11 (top-left area).
> 
> Another possibility, I am investigating now, is a ground loop and a
> main-supply voltage-dependency, although the whole USB OTG part is
> on a completely different supply rail, the GNDs are shared.
> 
> I am investigating in all directions at the moment ;-)
> 

Would you please measure the voltage of vbus within 1s at below two
conditions:

- Just connect cable
- Just disconnect cable

> 
> I also switched to CDC/EEM to make sure it has nothing to do with RNDIS,
> and the problem is still present. So the error must be on a lower level.
> 
> --
> 
> You could try to reproduce it with a MCIMX6Q-SDB and varying the main
> supply voltage between minimum and maximum allowed voltage levels. For
> example: Plug OTG in once at the minimum and once at the maximum level,
> see if it behaves differently.
> But this is just one of my desperate theories at the moment..
> 

Sorry, I have no equipment which can change the voltage of main supplier
now.

-- 

Best Regards,
Peter Chen

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