Re: [PATCH] xhci: Fix HIK camera control timeout on Etron hosts

[Michal Pecio <michal.pecio@gmail.com>]

On Tue, 3 Nov 2026 09:01:50 +0800, Kuangyi Chiang wrote:
> However, we captured USB traces using a protocol analyzer and
> observed different behavior between the failing and successful
> cases.
> 
> In the failing case, the device ACKed the DATA stage but kept
> NAKing the STATUS stage until the transfer timed out.
> 
> In the successful case, the device initially NAKed the DATA stage,
> then ACKed it, and the STATUS stage completed successfully.
> 
> We haven't determined the root cause yet.
> 
> In our tests, adding a 1 ms delay to both the UAC and UVC
> control request paths prevented the timeouts.

Could it be a device bug triggered by timing? Some xHCI controllers
perform control transfers faster than others - we have seen anything
(IIRC) from complete transfer in a microframe, through one stage per
microframe, up to one stage per frame even for high-speed devices.
We are not aware of any way to influence this, besides delaying URB
submissions. I don't know how fast EHCI controllers are.

> > > So far, we have reproduced the issue with these xHCI hosts:
> > >
> > > ASMedia ASM1142 (1b21:1242)
> > > Etron EJ168 (1b6f:7023)
> > > Etron EJ188 (1b6f:7052)
> > > Intel xHCI (8086:8d31)  
> >
> > I don't know that Intel chip, but the others are quite buggy.
> >
> > Have you tried other HCs? Any successes?
> > IME, chips from NEC, Fresco, Renesas are more reliable.  
> 
> In our recent tests without the delay patches, we did not
> observe any timeouts on the following HCs:
> 
> AMD EHCI (1002:4396)
> AMD xHCI (1022:149c)
> ASMedia ASM1042A (1b21:1142)
> NEC xHCI (1033:0194)

ASM1042A surprises me, because ASMedia in general are among the fastest
ones, except AMD Promontory chipsets which are extremely slow. NEC was
slightly slower than the fastest chips IIRC. I'm not familiar with AMD
Matisse and have no idea what xHCI IP they put inside.

Purely out of curiosity, could you connect a USB 3.0 NIC like RTL8153
or AX88197 to Matisse and see if it breaks after a minute of:

  while :; do ifconfig <xxx> up ; ifconfig <xxx> down ; echo -n . ; done

I found this to be a 100% reliable way to detect ASMedia controllers,
including those in AMD Promontory chipsets. This is the periodic unlink
bug I mentioned, which is mostly mitigated by 7c0c31c66a7f9 in 7.3,
so the test is more effective on 7.2.

Regards,
Michal