CP2112 USB->I2C bridge not appearing in /dev

Question

I am trying to get a SiLabs CP2112 USB to I2C bridge working with my Pi. At some point in recent history I had it working just fine. I could plug in a CP2112 evaluation board and a new entry /dev/i2c-2 was created for a new I2C bus. For some reason this doesn't seem to work anymore. I've gone back to a stock Raspbian image and still can't get the device to appear as an I2C bus.

If I connect my CP2112 then lsusb gives me:

Bus 001 Device 006: ID 10c4:ea90 Cygnal Integrated Products, Inc.

dmesg shows nothing bad:

[ 87.010707] usb 1-1.5: Product: CP2112 HID USB-to-SMBus Bridge [ 87.010724] usb 1-1.5: Manufacturer: Silicon Laboratories [ 87.010740] usb 1-1.5: SerialNumber: 0043FFF3 [ 107.147142] usb 1-1.5: USB disconnect, device number 5 [ 1438.756308] usb 1-1.3: new full-speed USB device number 6 using dwc_otg [ 1438.864004] usb 1-1.3: New USB device found, idVendor=10c4, idProduct=ea90 [ 1438.864030] usb 1-1.3: New USB device strings: Mfr=1, Product=2, SerialNumber=3 [ 1438.864049] usb 1-1.3: Product: CP2112 HID USB-to-SMBus Bridge [ 1438.864066] usb 1-1.3: Manufacturer: Silicon Laboratories [ 1438.864082] usb 1-1.3: SerialNumber: 0043FFF3

And /var/log/syslog again shows nothing that looks bad:

Mar 11 12:40:58 raspberrypi kernel: [ 1438.756308] usb 1-1.3: new full-speed USB device number 6 using dwc_otg Mar 11 12:40:58 raspberrypi kernel: [ 1438.864004] usb 1-1.3: New USB device found, idVendor=10c4, idProduct=ea90 Mar 11 12:40:58 raspberrypi kernel: [ 1438.864030] usb 1-1.3: New USB device strings: Mfr=1, Product=2, SerialNumber=3 Mar 11 12:40:58 raspberrypi kernel: [ 1438.864049] usb 1-1.3: Product: CP2112 HID USB-to-SMBus Bridge Mar 11 12:40:58 raspberrypi kernel: [ 1438.864066] usb 1-1.3: Manufacturer: Silicon Laboratories Mar 11 12:40:58 raspberrypi kernel: [ 1438.864082] usb 1-1.3: SerialNumber: 0043FFF3 Mar 11 12:40:58 raspberrypi mtp-probe: checking bus 1, device 6: "/sys/devices/platform/soc/3f980000.usb/usb1/1-1/1-1.3" Mar 11 12:40:58 raspberrypi mtp-probe: bus: 1, device: 6 was not an MTP device

The i2c-dev module is loaded. I see there has been fairly recent work on the hid-cp2112 driver in the kernel, and others appear to be able to use the device with no problems.

Can anyone offer any help or advice? Thank you.

Answer 1

Answering my own questions to help others who may have the same problem.

The Kernel for the Pi is not compiled with the driver for the CP2112 selected as either a builtin or a loadable module. For the CP2112 to operate correctly as a USB->I2C bridge follow the guide here to rebuild the kernel, with the exception that before compiling/building you should modify the .config to allow the hid-cp2112 driver to be included as a builtin driver.

With the Kernel and modules built deploy them to your Pi/Pi2 by copying the built Kernel Image over the top of kernel.img/kernel7.img and copying the built lib folder to /lib of the Pi SD Card.

When connecting a CP2112 you should now see the I2C bus appear under /dev