Input: add userio module

Debugging input devices, specifically laptop touchpads, can be tricky
without having the physical device handy. Here we try to remedy that
with userio. This module allows an application to connect to a character
device provided by the kernel, and emulate any serio device. In
combination with userspace programs that can record PS/2 devices and
replay them through the /dev/userio device, this allows developers to
debug driver issues on the PS/2 level with devices simply by requesting
a recording from the user experiencing the issue without having to have
the physical hardware in front of them.

Signed-off-by: Stephen Chandler Paul <cpaul@redhat.com>
Reviewed-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

1 files changed, 70 insertions, 0 deletions

diff --git a/Documentation/input/userio.txt b/Documentation/input/userio.txt
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+			      The userio Protocol
+	     (c) 2015 Stephen Chandler Paul <thatslyude@gmail.com>
+			      Sponsored by Red Hat
+--------------------------------------------------------------------------------
+
+1. Introduction
+~~~~~~~~~~~~~~~
+  This module is intended to try to make the lives of input driver developers
+easier by allowing them to test various serio devices (mainly the various
+touchpads found on laptops) without having to have the physical device in front
+of them. userio accomplishes this by allowing any privileged userspace program
+to directly interact with the kernel's serio driver and control a virtual serio
+port from there.
+
+2. Usage overview
+~~~~~~~~~~~~~~~~~
+  In order to interact with the userio kernel module, one simply opens the
+/dev/userio character device in their applications. Commands are sent to the
+kernel module by writing to the device, and any data received from the serio
+driver is read as-is from the /dev/userio device. All of the structures and
+macros you need to interact with the device are defined in <linux/userio.h> and
+<linux/serio.h>.
+
+3. Command Structure
+~~~~~~~~~~~~~~~~~~~~
+  The struct used for sending commands to /dev/userio is as follows:
+
+	struct userio_cmd {
+		__u8 type;
+		__u8 data;
+	};
+
+  "type" describes the type of command that is being sent. This can be any one
+of the USERIO_CMD macros defined in <linux/userio.h>. "data" is the argument
+that goes along with the command. In the event that the command doesn't have an
+argument, this field can be left untouched and will be ignored by the kernel.
+Each command should be sent by writing the struct directly to the character
+device. In the event that the command you send is invalid, an error will be
+returned by the character device and a more descriptive error will be printed
+to the kernel log. Only one command can be sent at a time, any additional data
+written to the character device after the initial command will be ignored.
+  To close the virtual serio port, just close /dev/userio.
+
+4. Commands
+~~~~~~~~~~~
+
+4.1 USERIO_CMD_REGISTER
+~~~~~~~~~~~~~~~~~~~~~~~
+  Registers the port with the serio driver and begins transmitting data back and
+forth. Registration can only be performed once a port type is set with
+USERIO_CMD_SET_PORT_TYPE. Has no argument.
+
+4.2 USERIO_CMD_SET_PORT_TYPE
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+  Sets the type of port we're emulating, where "data" is the port type being
+set. Can be any of the macros from <linux/serio.h>. For example: SERIO_8042
+would set the port type to be a normal PS/2 port.
+
+4.3 USERIO_CMD_SEND_INTERRUPT
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+  Sends an interrupt through the virtual serio port to the serio driver, where
+"data" is the interrupt data being sent.
+
+5. Userspace tools
+~~~~~~~~~~~~~~~~~~
+  The userio userspace tools are able to record PS/2 devices using some of the
+debugging information from i8042, and play back the devices on /dev/userio. The
+latest version of these tools can be found at:
+
+	https://github.com/Lyude/ps2emu