Re: [PATCH RESEND] HID: New hid-cp2112 driver.

[David Barksdale]

On 08/28/2013 07:57 AM, Jiri Kosina wrote:
>
> [ adding Benjamin to CC ]
>
> On Tue, 27 Aug 2013, David Barksdale wrote:
>
>> This patch adds support for the Silicon Labs CP2112 "Single-Chip
>> HID USB to SMBus Master Bridge."
>>
>> I wrote this to support a USB temperature and humidity sensor I've
>> been working on. It's been tested by using SMBus byte-read,
>> byte-data-read/write, and word-data-read transfer modes to talk to
>> an I2C sensor. The other transfer modes have not been tested.
>>
>> Signed-off-by: David Barksdale <dbarksdale@xxxxxxxxxxx>
>>
>> --- drivers/hid/Kconfig      |   6 + drivers/hid/Makefile     |
>> 1 + drivers/hid/hid-core.c   |   3 + drivers/hid/hid-cp2112.c |
>> 504 +++++++++++++++++++++++++++++++++++++++++++++++ 4 files
>> changed, 514 insertions(+)
>>
>> diff --git a/drivers/hid/Kconfig b/drivers/hid/Kconfig index
>> 14ef6ab..1833948 100644 --- a/drivers/hid/Kconfig +++
>> b/drivers/hid/Kconfig @@ -175,6 +175,12 @@ config HID_PRODIKEYS
>> multimedia keyboard, but will lack support for the musical keyboard
>> and some additional multimedia keys.
>>
>> +config HID_CP2112 +    tristate "Silicon Labs CP2112 HID
>> USB-to-SMBus Bridge support" +    depends on USB_HID +
>> ---help--- +    Support for Silicon Labs CP2112 HID USB to SMBus
>> Master Bridge. +
>
> Hi David,
>
> this is rather difficult to get by quickly looking at the code, so
> I'd like to have a slightly better overview of what the device
> really is.
>
> Is it talking HID protocol on the SMBus? (if so, there is a hid-i2c
> transport driver for it already). But I guess this is not really the
> case, as you seem to be using the USB HID functionality as well.
>
> Thanks in advance for some more background.
>

The CP2112 is a USB HID device that provides an SMBus controller.
The datasheet can be found here: 
http://www.silabs.com/Support%20Documents/TechnicalDocs/CP2112.pdf
The interface specification here: 
http://www.silabs.com/Support%20Documents/TechnicalDocs/AN495.pdf
The host communicates with the CP2112 via HID reports. Device 
configuration uses feature reports and data transfer uses output and 
event reports.
I prototyped this in userspace using the /dev/hidraw interface and then 
wrote this driver to provide a real i2c adapter device.
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