Re: User space raw hid support

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Hi Chen

On Wed, Mar 14, 2012 at 12:47 PM, Ganir, Chen <chen.ganir@xxxxxx> wrote:
> Hi all.
>
> I'm currently working on a HID Over GATT Implementation (HID over Bluetooth Low energy).
>
> As part of the design, it is required to configure the HID subsystem from user space, configure a report descriptor with input/output/feature report points, and send/receive data from and to the kernel HID Subsystem, from user space.
>
> Is there anything already supporting this feature ? I was looking at hid-raw, but it is used to send raw data from user space to the hid device - I need to send raw hid from the device to the kernel.

What do you mean with that? hidraw uses the
hid_input/output_raw_report() callbacks which HIDP/USBHID provide.
They provide direct access to the HID channels. With the
Bluetooth-backend you can directly write to the L2CAP channels. I
don't understand what you mean with "device to the kernel".

Do you need something more low-level or more high-level? Currently,
HIDP/USBHID provide the transport layer and register themselves with
the HID core. The HID core parses the HID protocol and provides input
devices on top of it. I don't understand where in-between of this you
want the hooks to be?

> Our basic idea was to develop a new misc char driver, at /dev/uhid. This device will be opened for each remote device we have access to, configured, and then read/write the raw HID packets from the device directly to this driver. We would like our solution to be a simple proxy between the device and the HID system, and we do not want to include a HID parser in our code, to make sure latency stays as low as possible.

Does that mean you want to sit on top of the kernel HID parser or you
don't want any parser in between? /dev/uhid looks like a HID-backend
like HIDP/usbhid so hidraw seems to be perfect for this.

> Thanks for your assistance,
>
> Chen Ganir
> Texas Instruments.

Regards
David
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