HID: hidraw: Add additional hidraw input/output report ioctls.

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>

1 files changed, 43 insertions, 2 deletions

diff --git a/Documentation/hid/hidraw.rst b/Documentation/hid/hidraw.rst
index 4a4a0ba1f362..f41c1f0f6252 100644
--- a/Documentation/hid/hidraw.rst
+++ b/Documentation/hid/hidraw.rst
@@ -123,8 +123,49 @@ HIDIOCGFEATURE(len):
 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).
+reports, set the first byte to 0.  The returned report buffer will contain the
+report number in the first byte, followed by the report data read from the
+device.  For devices which do not use numbered reports, the report data will
+begin at the first byte of the returned buffer.
+
+HIDIOCSINPUT(len):
+	Send an Input Report
+
+This ioctl will send an input report to the device, using the control endpoint.
+In most cases, setting an input HID report on a device is meaningless and has
+no effect, but some devices may choose to use this to set or reset an initial
+state of a report.  The format of the buffer issued with this report is identical
+to that of HIDIOCSFEATURE.
+
+HIDIOCGINPUT(len):
+	Get an Input Report
+
+This ioctl will request an input report from the device using the control
+endpoint.  This is slower on most devices where a dedicated In endpoint exists
+for regular input reports, but allows the host to request the value of a
+specific report number.  Typically, this is used to request the initial states of
+an input report of a device, before an application listens for normal reports via
+the regular device read() interface.  The format of the buffer issued with this report
+is identical to that of HIDIOCGFEATURE.
+
+HIDIOCSOUTPUT(len):
+	Send an Output Report
+
+This ioctl will send an output report to the device, using the control endpoint.
+This is slower on most devices where a dedicated Out endpoint exists for regular
+output reports, but is added for completeness.  Typically, this is used to set
+the initial states of an output report of a device, before an application sends
+updates via the regular device write() interface. The format of the buffer issued
+with this report is identical to that of HIDIOCSFEATURE.
+
+HIDIOCGOUTPUT(len):
+	Get an Output Report
+
+This ioctl will request an output report from the device using the control
+endpoint.  Typically, this is used to retrive the initial state of
+an output report of a device, before an application updates it as necessary either
+via a HIDIOCSOUTPUT request, or the regular device write() interface.  The format
+of the buffer issued with this report is identical to that of HIDIOCGFEATURE.
 
 Example
 -------