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Currently the hidraw module can only read and write feature HID reports on demand, via dedicated ioctls. Input reports are read from the device through the read() interface, while output reports are written through the write interface(). This is insufficient; it is desirable in many situations to be able to read and write input and output reports through the control interface to cover additional scenarios: - Reading an input report by its report ID, to get initial state - Writing an input report, to set initial input state in the device - Reading an output report by its report ID, to obtain current state - Writing an output report by its report ID, out of band This patch adds these missing ioctl requests to read and write the remaining HID report types. Note that not all HID backends will neccesarily support this (e.g. while the USB link layer supports setting Input reports, others may not). Also included are documentation and example updates. The current hidraw documentation states that feature reports read from the device does *not* include the report ID, however this is not the case and the returned report will have its report ID prepended by conforming HID devices, as the report data sent from the device over the control endpoint must be indentical in format to those sent over the regular transport. Signed-off-by: Dean Camera <dean@fourwalledcubicle.com> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
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7.3 KiB
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180 lines
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================================================================
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HIDRAW - Raw Access to USB and Bluetooth Human Interface Devices
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================================================================
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The hidraw driver provides a raw interface to USB and Bluetooth Human
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Interface Devices (HIDs). It differs from hiddev in that reports sent and
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received are not parsed by the HID parser, but are sent to and received from
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the device unmodified.
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Hidraw should be used if the userspace application knows exactly how to
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communicate with the hardware device, and is able to construct the HID
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reports manually. This is often the case when making userspace drivers for
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custom HID devices.
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Hidraw is also useful for communicating with non-conformant HID devices
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which send and receive data in a way that is inconsistent with their report
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descriptors. Because hiddev parses reports which are sent and received
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through it, checking them against the device's report descriptor, such
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communication with these non-conformant devices is impossible using hiddev.
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Hidraw is the only alternative, short of writing a custom kernel driver, for
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these non-conformant devices.
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A benefit of hidraw is that its use by userspace applications is independent
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of the underlying hardware type. Currently, Hidraw is implemented for USB
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and Bluetooth. In the future, as new hardware bus types are developed which
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use the HID specification, hidraw will be expanded to add support for these
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new bus types.
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Hidraw uses a dynamic major number, meaning that udev should be relied on to
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create hidraw device nodes. Udev will typically create the device nodes
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directly under /dev (eg: /dev/hidraw0). As this location is distribution-
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and udev rule-dependent, applications should use libudev to locate hidraw
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devices attached to the system. There is a tutorial on libudev with a
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working example at:
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http://www.signal11.us/oss/udev/
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The HIDRAW API
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---------------
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read()
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-------
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read() will read a queued report received from the HID device. On USB
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devices, the reports read using read() are the reports sent from the device
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on the INTERRUPT IN endpoint. By default, read() will block until there is
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a report available to be read. read() can be made non-blocking, by passing
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the O_NONBLOCK flag to open(), or by setting the O_NONBLOCK flag using
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fcntl().
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On a device which uses numbered reports, the first byte of the returned data
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will be the report number; the report data follows, beginning in the second
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byte. For devices which do not use numbered reports, the report data
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will begin at the first byte.
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write()
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-------
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The write() function will write a report to the device. For USB devices, if
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the device has an INTERRUPT OUT endpoint, the report will be sent on that
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endpoint. If it does not, the report will be sent over the control endpoint,
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using a SET_REPORT transfer.
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The first byte of the buffer passed to write() should be set to the report
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number. If the device does not use numbered reports, the first byte should
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be set to 0. The report data itself should begin at the second byte.
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ioctl()
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-------
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Hidraw supports the following ioctls:
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HIDIOCGRDESCSIZE:
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Get Report Descriptor Size
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This ioctl will get the size of the device's report descriptor.
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HIDIOCGRDESC:
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Get Report Descriptor
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This ioctl returns the device's report descriptor using a
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hidraw_report_descriptor struct. Make sure to set the size field of the
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hidraw_report_descriptor struct to the size returned from HIDIOCGRDESCSIZE.
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HIDIOCGRAWINFO:
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Get Raw Info
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This ioctl will return a hidraw_devinfo struct containing the bus type, the
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vendor ID (VID), and product ID (PID) of the device. The bus type can be one
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of::
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- BUS_USB
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- BUS_HIL
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- BUS_BLUETOOTH
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- BUS_VIRTUAL
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which are defined in uapi/linux/input.h.
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HIDIOCGRAWNAME(len):
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Get Raw Name
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This ioctl returns a string containing the vendor and product strings of
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the device. The returned string is Unicode, UTF-8 encoded.
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HIDIOCGRAWPHYS(len):
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Get Physical Address
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This ioctl returns a string representing the physical address of the device.
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For USB devices, the string contains the physical path to the device (the
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USB controller, hubs, ports, etc). For Bluetooth devices, the string
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contains the hardware (MAC) address of the device.
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HIDIOCSFEATURE(len):
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Send a Feature Report
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This ioctl will send a feature report to the device. Per the HID
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specification, feature reports are always sent using the control endpoint.
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Set the first byte of the supplied buffer to the report number. For devices
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which do not use numbered reports, set the first byte to 0. The report data
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begins in the second byte. Make sure to set len accordingly, to one more
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than the length of the report (to account for the report number).
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HIDIOCGFEATURE(len):
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Get a Feature Report
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This ioctl will request a feature report from the device using the control
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endpoint. The first byte of the supplied buffer should be set to the report
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number of the requested report. For devices which do not use numbered
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reports, set the first byte to 0. The returned report buffer will contain the
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report number in the first byte, followed by the report data read from the
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device. For devices which do not use numbered reports, the report data will
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begin at the first byte of the returned buffer.
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HIDIOCSINPUT(len):
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Send an Input Report
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This ioctl will send an input report to the device, using the control endpoint.
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In most cases, setting an input HID report on a device is meaningless and has
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no effect, but some devices may choose to use this to set or reset an initial
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state of a report. The format of the buffer issued with this report is identical
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to that of HIDIOCSFEATURE.
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HIDIOCGINPUT(len):
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Get an Input Report
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This ioctl will request an input report from the device using the control
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endpoint. This is slower on most devices where a dedicated In endpoint exists
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for regular input reports, but allows the host to request the value of a
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specific report number. Typically, this is used to request the initial states of
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an input report of a device, before an application listens for normal reports via
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the regular device read() interface. The format of the buffer issued with this report
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is identical to that of HIDIOCGFEATURE.
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HIDIOCSOUTPUT(len):
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Send an Output Report
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This ioctl will send an output report to the device, using the control endpoint.
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This is slower on most devices where a dedicated Out endpoint exists for regular
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output reports, but is added for completeness. Typically, this is used to set
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the initial states of an output report of a device, before an application sends
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updates via the regular device write() interface. The format of the buffer issued
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with this report is identical to that of HIDIOCSFEATURE.
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HIDIOCGOUTPUT(len):
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Get an Output Report
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This ioctl will request an output report from the device using the control
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endpoint. Typically, this is used to retrive the initial state of
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an output report of a device, before an application updates it as necessary either
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via a HIDIOCSOUTPUT request, or the regular device write() interface. The format
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of the buffer issued with this report is identical to that of HIDIOCGFEATURE.
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Example
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-------
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In samples/, find hid-example.c, which shows examples of read(), write(),
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and all the ioctls for hidraw. The code may be used by anyone for any
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purpose, and can serve as a starting point for developing applications using
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hidraw.
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Document by:
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Alan Ott <alan@signal11.us>, Signal 11 Software
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