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

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Date:	Thu, 29 Aug 2013 08:51:13 -0500
From:	David Barksdale <dbarksdale@...ogix.com>
To:	Jiri Kosina <jkosina@...e.cz>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Benjamin Tissoires <benjamin.tissoires@...hat.com>
Subject: Re: [PATCH RESEND] HID: New hid-cp2112 driver.

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@...ogix.com>
>>
>> ---
>>   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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