diff --git a/Documentation/input/userio.txt b/Documentation/input/userio.txt
new file mode 100644
index 0000000000000000000000000000000000000000..0880c0f447a6cee8158432fff7bb6c30c6af8d8c
--- /dev/null
+++ b/Documentation/input/userio.txt
@@ -0,0 +1,70 @@
+ 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
diff --git a/MAINTAINERS b/MAINTAINERS
index 797236befd279bef6bf7c0c074b132d4bf6f9380..ba59bd7b3557ccc8fcf25e6c2667bd311dee53f2 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -11100,6 +11100,12 @@ S: Maintained
F: drivers/media/v4l2-core/videobuf2-*
F: include/media/videobuf2-*
+VIRTUAL SERIO DEVICE DRIVER
+M: Stephen Chandler Paul <thatslyude@gmail.com>
+S: Maintained
+F: drivers/input/serio/userio.c
+F: include/uapi/linux/userio.h
+
VIRTIO CONSOLE DRIVER
M: Amit Shah <amit.shah@redhat.com>
L: virtualization@lists.linux-foundation.org
diff --git a/drivers/input/serio/Kconfig b/drivers/input/serio/Kconfig
index 200841b77edb85b22caf110f4693443957354915..c3d05b4d3118d908434eb594659a97e0b4703b05 100644
--- a/drivers/input/serio/Kconfig
+++ b/drivers/input/serio/Kconfig
@@ -292,4 +292,18 @@ config SERIO_SUN4I_PS2
To compile this driver as a module, choose M here: the
module will be called sun4i-ps2.
+config USERIO
+ tristate "User space serio port driver support"
+ help
+ Say Y here if you want to support user level drivers for serio
+ subsystem accessible under char device 10:240 - /dev/userio. Using
+ this facility userspace programs can implement serio ports that
+ will be used by the standard in-kernel serio consumer drivers,
+ such as psmouse and atkbd.
+
+ To compile this driver as a module, choose M here: the module will be
+ called userio.
+
+ If you are unsure, say N.
+
endif
diff --git a/drivers/input/serio/Makefile b/drivers/input/serio/Makefile
index c600089b7a349f2c05a624d27b5bbaeb646c9c45..2374ef9b33d788cee5693bb52905aabcd965df61 100644
--- a/drivers/input/serio/Makefile
+++ b/drivers/input/serio/Makefile
@@ -30,3 +30,4 @@ obj-$(CONFIG_SERIO_APBPS2) += apbps2.o
obj-$(CONFIG_SERIO_OLPC_APSP) += olpc_apsp.o
obj-$(CONFIG_HYPERV_KEYBOARD) += hyperv-keyboard.o
obj-$(CONFIG_SERIO_SUN4I_PS2) += sun4i-ps2.o
+obj-$(CONFIG_USERIO) += userio.o
diff --git a/drivers/input/serio/userio.c b/drivers/input/serio/userio.c
new file mode 100644
index 0000000000000000000000000000000000000000..df1fd41860ac90591a6927b927ef2638c7491861
--- /dev/null
+++ b/drivers/input/serio/userio.c
@@ -0,0 +1,285 @@
+/*
+ * userio kernel serio device emulation module
+ * Copyright (C) 2015 Red Hat
+ * Copyright (C) 2015 Stephen Chandler Paul <thatslyude@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or (at
+ * your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
+ * General Public License for more details.
+ */
+
+#include <linux/circ_buf.h>
+#include <linux/mutex.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/serio.h>
+#include <linux/slab.h>
+#include <linux/fs.h>
+#include <linux/miscdevice.h>
+#include <linux/sched.h>
+#include <linux/poll.h>
+#include <uapi/linux/userio.h>
+
+#define USERIO_NAME "userio"
+#define USERIO_BUFSIZE 16
+
+static struct miscdevice userio_misc;
+
+struct userio_device {
+ struct serio *serio;
+ struct mutex mutex;
+
+ bool running;
+
+ u8 head;
+ u8 tail;
+
+ spinlock_t buf_lock;
+ unsigned char buf[USERIO_BUFSIZE];
+
+ wait_queue_head_t waitq;
+};
+
+/**
+ * userio_device_write - Write data from serio to a userio device in userspace
+ * @id: The serio port for the userio device
+ * @val: The data to write to the device
+ */
+static int userio_device_write(struct serio *id, unsigned char val)
+{
+ struct userio_device *userio = id->port_data;
+ unsigned long flags;
+
+ spin_lock_irqsave(&userio->buf_lock, flags);
+
+ userio->buf[userio->head] = val;
+ userio->head = (userio->head + 1) % USERIO_BUFSIZE;
+
+ if (userio->head == userio->tail)
+ dev_warn(userio_misc.this_device,
+ "Buffer overflowed, userio client isn't keeping up");
+
+ spin_unlock_irqrestore(&userio->buf_lock, flags);
+
+ wake_up_interruptible(&userio->waitq);
+
+ return 0;
+}
+
+static int userio_char_open(struct inode *inode, struct file *file)
+{
+ struct userio_device *userio;
+
+ userio = kzalloc(sizeof(struct userio_device), GFP_KERNEL);
+ if (!userio)
+ return -ENOMEM;
+
+ mutex_init(&userio->mutex);
+ spin_lock_init(&userio->buf_lock);
+ init_waitqueue_head(&userio->waitq);
+
+ userio->serio = kzalloc(sizeof(struct serio), GFP_KERNEL);
+ if (!userio->serio) {
+ kfree(userio);
+ return -ENOMEM;
+ }
+
+ userio->serio->write = userio_device_write;
+ userio->serio->port_data = userio;
+
+ file->private_data = userio;
+
+ return 0;
+}
+
+static int userio_char_release(struct inode *inode, struct file *file)
+{
+ struct userio_device *userio = file->private_data;
+
+ if (userio->running) {
+ /*
+ * Don't free the serio port here, serio_unregister_port()
+ * does it for us.
+ */
+ serio_unregister_port(userio->serio);
+ } else {
+ kfree(userio->serio);
+ }
+
+ kfree(userio);
+
+ return 0;
+}
+
+static ssize_t userio_char_read(struct file *file, char __user *user_buffer,
+ size_t count, loff_t *ppos)
+{
+ struct userio_device *userio = file->private_data;
+ int error;
+ size_t nonwrap_len, copylen;
+ unsigned char buf[USERIO_BUFSIZE];
+ unsigned long flags;
+
+ /*
+ * By the time we get here, the data that was waiting might have
+ * been taken by another thread. Grab the buffer lock and check if
+ * there's still any data waiting, otherwise repeat this process
+ * until we have data (unless the file descriptor is non-blocking
+ * of course).
+ */
+ for (;;) {
+ spin_lock_irqsave(&userio->buf_lock, flags);
+
+ nonwrap_len = CIRC_CNT_TO_END(userio->head,
+ userio->tail,
+ USERIO_BUFSIZE);
+ copylen = min(nonwrap_len, count);
+ if (copylen) {
+ memcpy(buf, &userio->buf[userio->tail], copylen);
+ userio->tail = (userio->tail + copylen) %
+ USERIO_BUFSIZE;
+ }
+
+ spin_unlock_irqrestore(&userio->buf_lock, flags);
+
+ if (nonwrap_len)
+ break;
+
+ /* buffer was/is empty */
+ if (file->f_flags & O_NONBLOCK)
+ return -EAGAIN;
+
+ /*
+ * count == 0 is special - no IO is done but we check
+ * for error conditions (see above).
+ */
+ if (count == 0)
+ return 0;
+
+ error = wait_event_interruptible(userio->waitq,
+ userio->head != userio->tail);
+ if (error)
+ return error;
+ }
+
+ if (copylen)
+ if (copy_to_user(user_buffer, buf, copylen))
+ return -EFAULT;
+
+ return copylen;
+}
+
+static ssize_t userio_char_write(struct file *file, const char __user *buffer,
+ size_t count, loff_t *ppos)
+{
+ struct userio_device *userio = file->private_data;
+ struct userio_cmd cmd;
+ int error;
+
+ if (count != sizeof(cmd)) {
+ dev_warn(userio_misc.this_device, "Invalid payload size\n");
+ return -EINVAL;
+ }
+
+ if (copy_from_user(&cmd, buffer, sizeof(cmd)))
+ return -EFAULT;
+
+ error = mutex_lock_interruptible(&userio->mutex);
+ if (error)
+ return error;
+
+ switch (cmd.type) {
+ case USERIO_CMD_REGISTER:
+ if (!userio->serio->id.type) {
+ dev_warn(userio_misc.this_device,
+ "No port type given on /dev/userio\n");
+
+ error = -EINVAL;
+ goto out;
+ }
+
+ if (userio->running) {
+ dev_warn(userio_misc.this_device,
+ "Begin command sent, but we're already running\n");
+ error = -EBUSY;
+ goto out;
+ }
+
+ userio->running = true;
+ serio_register_port(userio->serio);
+ break;
+
+ case USERIO_CMD_SET_PORT_TYPE:
+ if (userio->running) {
+ dev_warn(userio_misc.this_device,
+ "Can't change port type on an already running userio instance\n");
+ error = -EBUSY;
+ goto out;
+ }
+
+ userio->serio->id.type = cmd.data;
+ break;
+
+ case USERIO_CMD_SEND_INTERRUPT:
+ if (!userio->running) {
+ dev_warn(userio_misc.this_device,
+ "The device must be registered before sending interrupts\n");
+ error = -ENODEV;
+ goto out;
+ }
+
+ serio_interrupt(userio->serio, cmd.data, 0);
+ break;
+
+ default:
+ error = -EOPNOTSUPP;
+ goto out;
+ }
+
+out:
+ mutex_unlock(&userio->mutex);
+ return error ?: count;
+}
+
+static unsigned int userio_char_poll(struct file *file, poll_table *wait)
+{
+ struct userio_device *userio = file->private_data;
+
+ poll_wait(file, &userio->waitq, wait);
+
+ if (userio->head != userio->tail)
+ return POLLIN | POLLRDNORM;
+
+ return 0;
+}
+
+static const struct file_operations userio_fops = {
+ .owner = THIS_MODULE,
+ .open = userio_char_open,
+ .release = userio_char_release,
+ .read = userio_char_read,
+ .write = userio_char_write,
+ .poll = userio_char_poll,
+ .llseek = no_llseek,
+};
+
+static struct miscdevice userio_misc = {
+ .fops = &userio_fops,
+ .minor = USERIO_MINOR,
+ .name = USERIO_NAME,
+};
+module_driver(userio_misc, misc_register, misc_deregister);
+
+MODULE_ALIAS_MISCDEV(USERIO_MINOR);
+MODULE_ALIAS("devname:" USERIO_NAME);
+
+MODULE_AUTHOR("Stephen Chandler Paul <thatslyude@gmail.com>");
+MODULE_DESCRIPTION("Virtual Serio Device Support");
+MODULE_LICENSE("GPL");
diff --git a/include/linux/miscdevice.h b/include/linux/miscdevice.h
index 81f6e427ba6bbb9b65f52a5d5937c39aee0c0125..5430374659734ae74ea27e8fb28a126976482b26 100644
--- a/include/linux/miscdevice.h
+++ b/include/linux/miscdevice.h
@@ -49,6 +49,7 @@
#define LOOP_CTRL_MINOR 237
#define VHOST_NET_MINOR 238
#define UHID_MINOR 239
+#define USERIO_MINOR 240
#define MISC_DYNAMIC_MINOR 255
struct device;
diff --git a/include/uapi/linux/userio.h b/include/uapi/linux/userio.h
new file mode 100644
index 0000000000000000000000000000000000000000..37d147f0a13a72c873931c9f2e7eaf0bdf87c3c8
--- /dev/null
+++ b/include/uapi/linux/userio.h
@@ -0,0 +1,44 @@
+/*
+ * userio: virtual serio device support
+ * Copyright (C) 2015 Red Hat
+ * Copyright (C) 2015 Lyude (Stephen Chandler Paul) <cpaul@redhat.com>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ * FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
+ * details.
+ *
+ * This is the public header used for user-space communication with the userio
+ * driver. __attribute__((__packed__)) is used for all structs to keep ABI
+ * compatibility between all architectures.
+ */
+
+#ifndef _USERIO_H
+#define _USERIO_H
+
+#include <linux/types.h>
+
+enum userio_cmd_type {
+ USERIO_CMD_REGISTER = 0,
+ USERIO_CMD_SET_PORT_TYPE = 1,
+ USERIO_CMD_SEND_INTERRUPT = 2
+};
+
+/*
+ * userio Commands
+ * All commands sent to /dev/userio are encoded using this structure. The type
+ * field should contain a USERIO_CMD* value that indicates what kind of command
+ * is being sent to userio. The data field should contain the accompanying
+ * argument for the command, if there is one.
+ */
+struct userio_cmd {
+ __u8 type;
+ __u8 data;
+} __attribute__((__packed__));
+
+#endif /* !_USERIO_H */