mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-12-23 20:53:53 +08:00
c54ea4918c
Documenation for the hidraw driver, with sample program. Signed-off-by: Alan Ott <alan@signal11.us> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
120 lines
5.3 KiB
Plaintext
120 lines
5.3 KiB
Plaintext
HIDRAW - Raw Access to USB and Bluetooth Human Interface Devices
|
|
==================================================================
|
|
|
|
The hidraw driver provides a raw interface to USB and Bluetooth Human
|
|
Interface Devices (HIDs). It differs from hiddev in that reports sent and
|
|
received are not parsed by the HID parser, but are sent to and received from
|
|
the device unmodified.
|
|
|
|
Hidraw should be used if the userspace application knows exactly how to
|
|
communicate with the hardware device, and is able to construct the HID
|
|
reports manually. This is often the case when making userspace drivers for
|
|
custom HID devices.
|
|
|
|
Hidraw is also useful for communicating with non-conformant HID devices
|
|
which send and receive data in a way that is inconsistent with their report
|
|
descriptors. Because hiddev parses reports which are sent and received
|
|
through it, checking them against the device's report descriptor, such
|
|
communication with these non-conformant devices is impossible using hiddev.
|
|
Hidraw is the only alternative, short of writing a custom kernel driver, for
|
|
these non-conformant devices.
|
|
|
|
A benefit of hidraw is that its use by userspace applications is independent
|
|
of the underlying hardware type. Currently, Hidraw is implemented for USB
|
|
and Bluetooth. In the future, as new hardware bus types are developed which
|
|
use the HID specification, hidraw will be expanded to add support for these
|
|
new bus types.
|
|
|
|
Hidraw uses a dynamic major number, meaning that udev should be relied on to
|
|
create hidraw device nodes. Udev will typically create the device nodes
|
|
directly under /dev (eg: /dev/hidraw0). As this location is distribution-
|
|
and udev rule-dependent, applications should use libudev to locate hidraw
|
|
devices attached to the system. There is a tutorial on libudev with a
|
|
working example at:
|
|
http://www.signal11.us/oss/udev/
|
|
|
|
The HIDRAW API
|
|
---------------
|
|
|
|
read()
|
|
-------
|
|
read() will read a queued report received from the HID device. On USB
|
|
devices, the reports read using read() are the reports sent from the device
|
|
on the INTERRUPT IN endpoint. By default, read() will block until there is
|
|
a report available to be read. read() can be made non-blocking, by passing
|
|
the O_NONBLOCK flag to open(), or by setting the O_NONBLOCK flag using
|
|
fcntl().
|
|
|
|
On a device which uses numbered reports, the first byte of the returned data
|
|
will be the report number; the report data follows, beginning in the second
|
|
byte. For devices which do not use numbered reports, the report data
|
|
will begin at the first byte.
|
|
|
|
write()
|
|
--------
|
|
The write() function will write a report to the device. For USB devices, if
|
|
the device has an INTERRUPT OUT endpoint, the report will be sent on that
|
|
endpoint. If it does not, the report will be sent over the control endpoint,
|
|
using a SET_REPORT transfer.
|
|
|
|
The first byte of the buffer passed to write() should be set to the report
|
|
number. If the device does not use numbered reports, the first byte should
|
|
be set to 0. The report data itself should begin at the second byte.
|
|
|
|
ioctl()
|
|
--------
|
|
Hidraw supports the following ioctls:
|
|
|
|
HIDIOCGRDESCSIZE: Get Report Descriptor Size
|
|
This ioctl will get the size of the device's report descriptor.
|
|
|
|
HIDIOCGRDESC: Get Report Descriptor
|
|
This ioctl returns the device's report descriptor using a
|
|
hidraw_report_descriptor struct. Make sure to set the size field of the
|
|
hidraw_report_descriptor struct to the size returned from HIDIOCGRDESCSIZE.
|
|
|
|
HIDIOCGRAWINFO: Get Raw Info
|
|
This ioctl will return a hidraw_devinfo struct containing the bus type, the
|
|
vendor ID (VID), and product ID (PID) of the device. The bus type can be one
|
|
of:
|
|
BUS_USB
|
|
BUS_HIL
|
|
BUS_BLUETOOTH
|
|
BUS_VIRTUAL
|
|
which are defined in linux/input.h.
|
|
|
|
HIDIOCGRAWNAME(len): Get Raw Name
|
|
This ioctl returns a string containing the vendor and product strings of
|
|
the device. The returned string is Unicode, UTF-8 encoded.
|
|
|
|
HIDIOCGRAWPHYS(len): Get Physical Address
|
|
This ioctl returns a string representing the physical address of the device.
|
|
For USB devices, the string contains the physical path to the device (the
|
|
USB controller, hubs, ports, etc). For Bluetooth devices, the string
|
|
contains the hardware (MAC) address of the device.
|
|
|
|
HIDIOCSFEATURE(len): Send a Feature Report
|
|
This ioctl will send a feature report to the device. Per the HID
|
|
specification, feature reports are always sent using the control endpoint.
|
|
Set the first byte of the supplied buffer to the report number. For devices
|
|
which do not use numbered reports, set the first byte to 0. The report data
|
|
begins in the second byte. Make sure to set len accordingly, to one more
|
|
than the length of the report (to account for the report number).
|
|
|
|
HIDIOCGFEATURE(len): Get a Feature Report
|
|
This ioctl will request a feature report from the device using the control
|
|
endpoint. The first byte of the supplied buffer should be set to the report
|
|
number of the requested report. For devices which do not use numbered
|
|
reports, set the first byte to 0. The report will be returned starting at
|
|
the first byte of the buffer (ie: the report number is not returned).
|
|
|
|
Example
|
|
---------
|
|
In samples/, find hid-example.c, which shows examples of read(), write(),
|
|
and all the ioctls for hidraw. The code may be used by anyone for any
|
|
purpose, and can serve as a starting point for developing applications using
|
|
hidraw.
|
|
|
|
Document by:
|
|
Alan Ott <alan@signal11.us>, Signal 11 Software
|