Not enough bandwidth with Magewell XI100DUSB-HDMI

[Philipp Zabel <philipp.zabel@gmail.com>]

Hi,

On Fri, Jan 19, 2018 at 2:10 PM, Michael Tretter
<m.tretter@pengutronix.de> wrote:
> I found the old thread and it sounds exactly like my issue. Different
> camera, but same xHCI controller.

I have exactly the same issue with the xHCI controller of my laptop and
"Oculus Sensor" USB3 isochronous mostly-UVC cameras:

00:14.0 USB controller: Intel Corporation Wildcat Point-LP USB xHCI
Controller (rev 03) (prog-if 30 [XHCI])
    Subsystem: Lenovo Wildcat Point-LP USB xHCI Controller
    Flags: bus master, medium devsel, latency 0, IRQ 44
    Memory at f2220000 (64-bit, non-prefetchable) [size=64K]
    Capabilities: [70] Power Management version 2
    Capabilities: [80] MSI: Enable+ Count=1/8 Maskable- 64bit+
    Kernel driver in use: xhci_hcd
    Kernel modules: xhci_pci

T:  Bus=02 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#=  4 Spd=5000 MxCh= 0
D:  Ver= 3.00 Cls=ef(misc ) Sub=02 Prot=01 MxPS= 9 #Cfgs=  1
P:  Vendor=2833 ProdID=0211 Rev= 0.00
S:  Manufacturer=Oculus VR
S:  Product=Rift Sensor
S:  SerialNumber=WMTD3034300BCT
C:* #Ifs= 2 Cfg#= 1 Atr=80 MxPwr=800mA
A:  FirstIf#= 0 IfCount= 2 Cls=ff(vend.) Sub=03 Prot=00
I:* If#= 0 Alt= 0 #EPs= 1 Cls=ff(vend.) Sub=01 Prot=00 Driver=uvcvideo
E:  Ad=83(I) Atr=03(Int.) MxPS=  32 Ivl=128ms
I:* If#= 1 Alt= 0 #EPs= 0 Cls=ff(vend.) Sub=02 Prot=00 Driver=uvcvideo
I:  If#= 1 Alt= 1 #EPs= 1 Cls=ff(vend.) Sub=02 Prot=00 Driver=uvcvideo
E:  Ad=81(I) Atr=05(Isoc) MxPS=1024 Ivl=125us
I:  If#= 1 Alt= 2 #EPs= 1 Cls=ff(vend.) Sub=02 Prot=00 Driver=uvcvideo
E:  Ad=81(I) Atr=05(Isoc) MxPS=1024 Ivl=125us

Any USB2 or USB3 device that I plug in while the first camera is streaming in
altsetting 1 or 2 causes the bandwidth error. The same happens when I try to
change the altsetting on an isochronous endpoint of an already plugged device.
While the camera is in altsetting 0, other devices can be probed and work.

> For some tests, I changed the xhci_change_max_exit_latency() function
> to ignore the requested MEL and set the MEL to 0. Now the USB devices
> are detected correctly.

Exactly the same thing helps here, as well. With this hack, streaming from two
of those cameras at the same time works without any apparent problem:

----------8<----------
        xhci_dbg_trace(xhci, trace_xhci_dbg_context_change,
---------->8----------

regards
Philipp
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diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index 297536c9fd00..3cb4a60d8822 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -4025,7 +4025,7 @@ static int __maybe_unused
xhci_change_max_exit_latency(struct xhci_hcd *xhci,
        ctrl_ctx->add_flags |= cpu_to_le32(SLOT_FLAG);
        slot_ctx = xhci_get_slot_ctx(xhci, command->in_ctx);
        slot_ctx->dev_info2 &= cpu_to_le32(~((u32) MAX_EXIT));
-       slot_ctx->dev_info2 |= cpu_to_le32(max_exit_latency);
+       slot_ctx->dev_info2 |= cpu_to_le32(0);
        slot_ctx->dev_state = 0;