[U-Boot] [PATCH 1/1] dwc2 USB controller hangs with lan78xx

[Peter Robinson]

On Tue, Jun 26, 2018 at 4:55 PM, Alexander Graf <agraf at suse.de> wrote:
> On 06/26/2018 02:47 PM, Peter Robinson wrote:
>>>>>
>>>>> This bug is the combination of dwc2 USB controller and lan78xx
>>>>> USB ethernet controller, which is the combination in use on
>>>>> the Raspberry Pi Model 3 B+.
>>>>>
>>>>> When the host attempts to receive a packet, but a packet has not
>>>>> arrived, the lan78xx controller responds by setting BIR
>>>>> (Bulk-In Empty Response) to NAK. Unfortunately, this hangs
>>>>> the USB controller and requires the USB controller to
>>>>> be reset.
>>>>>
>>>>> The fix proposed is to have the lan78xx controller respond
>>>>> by setting BIR to ZLP.
>>>>>
>>>>> Signed-off-by: Andrew Thomas <andrew.thomas at oracle.com>
>>>>
>>>> Tested-by: Peter Robinson <pbrobinson at gmail.com>
>>>>
>>>> Tested on the RPi 3B+ and certainly improves this situation a number
>>>> of Fedora users have seen.
>>>
>>>
>>>
>>> What exactly have you tested?
>>>
>>> Even with this patch, I am not reliably to reliably boot into grub. It
>>> almost seems as if the packet buffer keeps getting overwritten by newer
>>> packets so that by the time we process the old ones, the ones we wanted
>>> to
>>> see are gone.
>>
>> Booting to grub and then a local system, it's seemed improved in terms
>> of stability for me and a few other users, at least was more
>> consistent in getting to grub without "Rx: failed to receive: -5" but
>> then from the various testing different Fedora users have seen prior
>> to this patch it seems that the issue is very
>> network/cable/environment specific. I'm fairly certain that this patch
>> doesn't fix the problem but it at least appears from current reports
>> to improve the situation for some users.
>
>
> Improve, yes, but not solve it to a point where it's fully usable. And I
> don't think we have a full grasp on what's broken yet.

I completely agree, it makes the problem go away for a number of users
so it's not completely terrible and less people bothering me is a good
start IMO even if it's not the final fix.

> What I'm seeing here is that booting grub stalls within early bootup (where
> it loads modules) until I press any key on serial. Pressing a key on a USB
> keyboard does not help.
>
> Given that there are no interrupts enabled on the RPi at this point, I can
> only think of caches as the culprit for this breakage. But why did it work
> with the normal 3B then?

Different USB NIC, maybe the usb3 interface has a different impact on
the dwc2 interface. The lan78xx driver seemed to have had little use
in general before it landed in the 3B+ and had numerous issues in the
Linux driver that have been quickly addressed so I figured that the
u-boot driver is probably just as terrible. Due to other commitments
I've had little time to investigate that theory further though as my
understanding of low level usb isn't huge.

Peter