Re: [PATCH v3] Add virtio input device specification.

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Oct 23, 2018 at 03:04:51PM +0200, Gerd Hoffmann wrote:
> 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>

Great, thank you!

> ---
> 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