Re: Question regarding CDC NCM and VNC performance issue

[Hiago De Franco <hiagofranco@gmail.com>]

From: Hiago De Franco <hiago.franco@toradex.com>

Hi Oliver,

On 06.12.23 13:21, Oliver Neukum wrote:
> Before we proceed, however, your patch raises a fundamental question:
> Are we talking about gadget or host mode here?
> Could you please describe your setup in detail?

Sure, I'm running a Apalis iMX6QD 512MB, which is basically an ARM 32-bits
device with NXP iMX6QD. This device is running Linux with wayland, weston
and the neatvnc server, so I can access my app using a vnc client on my
host PC (also running Linux, Debian 12).

The device is connected to my host pc using a USB cable. The gadget is my
ARM device, which I'm configuring using the libusbgx to create a new
gadget called 'gncm'. The host, in this case, is my Debian PC. My device
is automatically configured to use the ip 192.168.11.1 and give to my PC,
using the udhcpd from busybox, the ip 192.168.11.2.

Everything works, when I connect the ARM device to my PC with the USB
cable, my Debian automatically detects as a new interface and get the
192.168.11.2 ip:

39: enx4224347674f3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc
fq_codel state UP group default qlen 1000
    link/ether 42:24:34:76:74:f3 brd ff:ff:ff:ff:ff:ff
    inet 192.168.11.2/24 brd 192.168.11.255 scope global dynamic
    noprefixroute enx4224347674f3
       valid_lft 863996sec preferred_lft 863996sec
    inet6 fe80::8959:d7da:f1fc:774e/64 scope link noprefixroute
       valid_lft forever preferred_lft forever

While on the device:

/ #
3: usb0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast qlen
1000
    link/ether 7a:c5:38:46:21:e5 brd ff:ff:ff:ff:ff:ff
    inet 192.168.11.1/24 scope global usb0
       valid_lft forever preferred_lft forever

/ # cat /sys/class/udc/ci_hdrc.0/function
gncm
/ # ls /sys/kernel/config/usb_gadget/gncm/
UDC              bMaxPacketSize0  functions        os_desc
bDeviceClass     bcdDevice        idProduct        strings
bDeviceProtocol  bcdUSB           idVendor
bDeviceSubClass  configs          max_speed

Finally, I open a VNC client on my host PC and connect to 192.168.11.1,
where the issue begins with it being very slow/frozen. After applying the
patch on the device (Apalis iMX6), now VNC runs smoothly.

Now I will also try to debug the driver on the PC host side.

Thanks and regards,
Hiago