[PATCH v3] Add virtio input device specification.

[Gerd Hoffmann <kraxel@redhat.com>]

Support has been added to the linux kernel version 4.1
and to qemu version 2.4.

Signed-off-by: Ladi Prosek <lprosek@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
v2->v3:
* add missing abs field to virtio_input_absinfo.

v1->v2 (by Ladi):
* added VIRTIO_INPUT_CFG_ID_DEVIDS / virtio_input_devids
* added normative statements and moved them all to
  \devicenormative and \drivernormative sections
* made it clearer that this specifies virtio transport,
  not evdev itself
* Michael's feedback on the incremental patch
* minor tweaks
---
 conformance.tex  |  18 ++++++
 content.tex      |   2 +
 virtio-input.tex | 194 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 214 insertions(+)
 create mode 100644 virtio-input.tex

diff --git a/conformance.tex b/conformance.tex
index 7b7df32..2486e9a 100644
--- a/conformance.tex
+++ b/conformance.tex
@@ -145,6 +145,15 @@ An SCSI host driver MUST conform to the following normative statements:
 \item \ref{drivernormative:Device Types / SCSI Host Device / Device Operation / Device Operation: eventq}
 \end{itemize}
 
+\subsection{Input Driver Conformance}\label{sec:Conformance / Driver Conformance / Input Driver Conformance}
+
+An input driver MUST conform to the following normative statements:
+
+\begin{itemize}
+\item \ref{drivernormative:Device Types / Input Device / Device Initialization}
+\item \ref{drivernormative:Device Types / Input Device / Device Operation}
+\end{itemize}
+
 \section{Device Conformance}\label{sec:Conformance / Device Conformance}
 
 A device MUST conform to the following normative statements:
@@ -265,6 +274,15 @@ An SCSI host device MUST conform to the following normative statements:
 \item \ref{devicenormative:Device Types / SCSI Host Device / Device Operation / Device Operation: eventq}
 \end{itemize}
 
+\subsection{Input Device Conformance}\label{sec:Conformance / Device Conformance / Input Device Conformance}
+
+An input device MUST conform to the following normative statements:
+
+\begin{itemize}
+\item \ref{devicenormative:Device Types / Input Device / Device Initialization}
+\item \ref{devicenormative:Device Types / Input Device / Device Operation}
+\end{itemize}
+
 \section{Legacy Interface: Transitional Device and
 Transitional Driver Conformance}\label{sec:Conformance / Legacy
 Interface: Transitional Device and 
diff --git a/content.tex b/content.tex
index d989d98..4c0c4c9 100644
--- a/content.tex
+++ b/content.tex
@@ -5641,6 +5641,8 @@ descriptor for the \field{sense_len}, \field{residual},
 \field{status_qualifier}, \field{status}, \field{response} and
 \field{sense} fields.
 
+\input{virtio-input.tex}
+
 \chapter{Reserved Feature Bits}\label{sec:Reserved Feature Bits}
 
 Currently there are three device-independent feature bits defined:
diff --git a/virtio-input.tex b/virtio-input.tex
new file mode 100644
index 0000000..044c714
--- /dev/null
+++ b/virtio-input.tex
@@ -0,0 +1,194 @@
+\section{Input Device}\label{sec:Device Types / Input Device}
+
+The virtio input device can be used to create virtual human interface
+devices such as keyboards, mice and tablets. An instance of the virtio
+device represents one such input device. Device behavior mirrors that
+of the evdev layer in Linux, making pass-through implementations on top
+of evdev easy.
+
+This specification defines how evdev events are transported
+over virtio and how the set of supported events is discovered by a driver.
+It does not, however, define the semantics of input events as this is
+dependent on the particular evdev implementation. For the list of events
+used by Linux input devices, see
+\href{https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/include/uapi/linux/input-event-codes.h}{include/uapi/linux/input-event-codes.h}
+in the Linux source tree.
+
+\subsection{Device ID}\label{sec:Device Types / Input Device / Device ID}
+
+18
+
+\subsection{Virtqueues}\label{sec:Device Types / Input Device / Virtqueues}
+
+\begin{description}
+\item[0] eventq
+\item[1] statusq
+\end{description}
+
+\subsection{Feature bits}\label{sec:Device Types / Input Device / Feature bits}
+
+None.
+
+\subsection{Device configuration layout}\label{sec:Device Types / Input Device / Device configuration layout}
+
+Device configuration holds all information the guest needs to handle
+the device, most importantly the events which are supported.
+
+\begin{lstlisting}
+enum virtio_input_config_select {
+	VIRTIO_INPUT_CFG_UNSET      = 0x00,
+	VIRTIO_INPUT_CFG_ID_NAME    = 0x01,
+	VIRTIO_INPUT_CFG_ID_SERIAL  = 0x02,
+	VIRTIO_INPUT_CFG_ID_DEVIDS  = 0x03,
+	VIRTIO_INPUT_CFG_PROP_BITS  = 0x10,
+	VIRTIO_INPUT_CFG_EV_BITS    = 0x11,
+	VIRTIO_INPUT_CFG_ABS_INFO   = 0x12,
+};
+
+struct virtio_input_absinfo {
+	le32  min;
+	le32  max;
+	le32  fuzz;
+	le32  flat;
+	le32  res;
+};
+
+struct virtio_input_devids {
+	le16  bustype;
+	le16  vendor;
+	le16  product;
+	le16  version;
+};
+
+struct virtio_input_config {
+	u8    select;
+	u8    subsel;
+	u8    size;
+	u8    reserved[5];
+	union {
+		char string[128];
+		u8   bitmap[128];
+		struct virtio_input_absinfo abs;
+		struct virtio_input_devids ids;
+	} u;
+};
+\end{lstlisting}
+
+To query a specific piece of information the driver sets
+\field{select} and \field{subsel} accordingly, then checks \field{size}
+to see how much information is available.  \field{size} can be
+zero if no information is available.  Strings do not include a
+NUL terminator. Related evdev ioctl names are provided for reference.
+\begin{description}
+
+\item[VIRTIO_INPUT_CFG_ID_NAME]
+\field{subsel} is zero.
+Returns the name of the device, in \field{u.string}.
+
+Similar to EVIOCGNAME ioctl for Linux evdev devices.
+
+\item[VIRTIO_INPUT_CFG_ID_SERIAL]
+\field{subsel} is zero.
+Returns the serial number of the device, in \field{u.string}.
+
+\item[VIRTIO_INPUT_CFG_ID_DEVIDS]
+\field{subsel} is zero.
+Returns ID information of the device, in \field{u.ids}.
+
+Similar to EVIOCGID ioctl for Linux evdev devices.
+
+\item[VIRTIO_INPUT_CFG_PROP_BITS]
+\field{subsel} is zero.
+Returns input properties of the device, in \field{u.bitmap}.
+Individual bits in the bitmap correspond to INPUT_PROP_*
+constants used by the underlying evdev implementation.
+
+Similar to EVIOCGPROP ioctl for Linux evdev devices.
+
+\item[VIRTIO_INPUT_CFG_EV_BITS]
+\field{subsel} specifies the event type using EV_*
+constants in the underlying evdev implementation. If
+\field{size} is non-zero the event type is supported and
+a bitmap of supported event codes is returned in \field{u.bitmap}.
+Individual bits in the bitmap correspond to
+implementation-defined input event codes, for example keys
+or pointing device axes.
+
+Similar to EVIOCGBIT ioctl for Linux evdev devices.
+
+\item[VIRTIO_INPUT_CFG_ABS_INFO]
+\field{subsel} specifies the absolute axis using ABS_*
+constants in the underlying evdev implementation.
+Information about the axis will be returned in \field{u.abs}.
+
+Similar to EVIOCGABS ioctl for Linux evdev devices.
+
+\end{description}
+
+\subsection{Device Initialization}\label{sec:Device Types / Input Device / Device Initialization}
+
+\begin{enumerate}
+\item The device is queried for supported event types and codes.
+\item The eventq is populated with receive buffers.
+\end{enumerate}
+
+\drivernormative{\subsubsection}{Device Initialization}{Device Types / Input Device / Device Initialization}
+A driver MUST set both \field{select} and \field{subsel} when querying
+  device configuration, in any order.
+
+A driver MUST NOT write to configuration fields other than \field{select}
+  and \field{subsel}.
+
+A driver SHOULD check the \field{size} field before accessing the
+  configuration information.
+
+\devicenormative{\subsubsection}{Device Initialization}{Device Types / Input Device / Device Initialization}
+A device MUST set the \field{size} field to zero if it doesn't support a
+  given \field{select} and \field{subsel} combination.
+
+\subsection{Device Operation}\label{sec:Device Types / Input Device / Device Operation}
+
+\begin{enumerate}
+\item Input events such as press and release events for keys and
+  buttons, and motion events for pointing devices are sent from
+  the device to the driver using the eventq.
+\item Status feedback such as keyboard LED updates are sent from the
+  driver to the device using the statusq.
+\item Both queues use the same virtio_input_event struct.
+  \field{type}, \field{code} and \field{value} are filled according to
+  the Linux input layer (evdev) interface, except that the fields are
+  in little endian byte order whereas the evdev ioctl interface uses
+  native endian-ness.
+\end{enumerate}
+
+\begin{lstlisting}
+struct virtio_input_event {
+	le16 type;
+	le16 code;
+	le32 value;
+};
+\end{lstlisting}
+
+\drivernormative{\subsubsection}{Device Operation}{Device Types / Input Device / Device Operation}
+
+A driver SHOULD keep the eventq populated with buffers. These buffers
+  MUST be device-writable and MUST be at least the size of
+  struct virtio_input_event.
+
+Buffers placed into the statusq by a driver MUST be at least the size
+  of struct virtio_input_event.
+
+A driver SHOULD ignore eventq input events it does not recognize. Note
+  that evdev devices generally maintain backward compatibility by sending
+  redundant events and relying on the consuming side using only the events
+  it understands and ignoring the rest.
+
+\devicenormative{\subsubsection}{Device Operation}{Device Types / Input Device / Device Operation}
+
+A device MAY drop input events if the eventq does not have enough
+  available buffers. It SHOULD NOT drop individual input events if
+  they are part of a sequence forming one input device update. For
+  example, a pointing device update typically consists of several
+  input events, one for each axis, and a terminating EV_SYN event.
+  A device SHOULD either buffer or drop the entire sequence.
+
-- 
2.9.3