Documentation: usb: HID function testing

3. ECM subset function

4. EEM function

5. FFS function

6. HID function

1. ACM function

On the device: start the function's userspace daemon, enable the gadget

On the host: use the USB function provided by the device

6. HID function

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The function is provided by usb_f_hid.ko module.

Function-specific configfs interface

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The function name to use when creating the function directory is "hid".

The HID function provides these attributes in its function directory:

	protocol	- HID protocol to use

	report_desc	- data to be used in HID reports, except data

			passed with /dev/hidg<X>

	report_length	- HID report length

	subclass	- HID subclass to use

For a keyboard the protocol and the subclass are 1, the report_length is 8,

while the report_desc is:

$ hd my_report_desc

00000000  05 01 09 06 a1 01 05 07  19 e0 29 e7 15 00 25 01  |..........)...%.|

00000010  75 01 95 08 81 02 95 01  75 08 81 03 95 05 75 01  |u.......u.....u.|

00000020  05 08 19 01 29 05 91 02  95 01 75 03 91 03 95 06  |....).....u.....|

00000030  75 08 15 00 25 65 05 07  19 00 29 65 81 00 c0     |u...%e....)e...|

0000003f

Such a sequence of bytes can be stored to the attribute with echo:

$ echo -ne \\x05\\x01\\x09\\x06\\xa1.....

Testing the HID function

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Device:

- create the gadget

- connect the gadget to a host, preferably not the one used

to control the gadget

- run a program which writes to /dev/hidg<N>, e.g.

a userspace program found in Documentation/usb/gadget_hid.txt:

$ ./hid_gadget_test /dev/hidg0 keyboard

Host:

- observe the keystrokes from the gadget