Re: [PATCH v2 1/1] virtio-video: Add virtio video device specification

Keiichi Watanabe
2020-01-07T13:24:47Z

Hi Dmitry,

On Mon, Jan 6, 2020 at 11:59 PM Dmitry Sepp <dmitry.sepp@opensynergy.com> wrote:
>
> Hi,
>
> a couple of new comments:
>
> On Mittwoch, 18. Dezember 2019 14:02:14 CET Keiichi Watanabe wrote:
> > From: Dmitry Sepp <dmitry.sepp@opensynergy.com>
> >
> > The virtio video encoder device and decoder device provide functionalities
> > to encode and decode video stream respectively.
> > Though video encoder and decoder are provided as different devices, they use
> > a same protocol.
> >
> > Signed-off-by: Dmitry Sepp <dmitry.sepp@opensynergy.com>
> > Signed-off-by: Keiichi Watanabe <keiichiw@chromium.org>
> > ---
> > content.tex | 1 +
> > virtio-video.tex | 579 +++++++++++++++++++++++++++++++++++++++++++++++
> > 2 files changed, 580 insertions(+)
> > create mode 100644 virtio-video.tex
> >
> > diff --git a/content.tex b/content.tex
> > index 556b373..9e56839 100644
> > --- a/content.tex
> > +++ b/content.tex
> > @@ -5743,6 +5743,7 @@ \subsubsection{Legacy Interface: Framing
> > Requirements}\label{sec:Device \input{virtio-vsock.tex}
> > \input{virtio-fs.tex}
> > \input{virtio-rpmb.tex}
> > +\input{virtio-video.tex}
> >
> > \chapter{Reserved Feature Bits}\label{sec:Reserved Feature Bits}
> >
> > diff --git a/virtio-video.tex b/virtio-video.tex
> > new file mode 100644
> > index 0000000..30e728d
> > --- /dev/null
> > +++ b/virtio-video.tex
> > @@ -0,0 +1,579 @@
> > +\section{Video Device}\label{sec:Device Types / Video Device}
> > +
> > +The virtio video encoder device and decoder device are virtual devices that
> > +supports encoding and decoding respectively. Though the encoder and the
> > decoder +are different devices, they use the same protocol.
> > +
> > +\subsection{Device ID}\label{sec:Device Types / Video Device / Device ID}
> > +
> > +\begin{description}
> > +\item[30] encoder device
> > +\item[31] decoder device
> > +\end{description}
> > +
> > +\subsection{Virtqueues}\label{sec:Device Types / Video Device / Virtqueues}
> > +
> > +\begin{description}
> > +\item[0] controlq - queue for sending control commands.
> > +\item[1] eventq - queue for sending events happened in the device.
> > +\end{description}
> > +
> > +\subsection{Feature bits}\label{sec:Device Types / Video Device / Feature
> > bits} +
> > +\begin{description}
> > +\item[VIRTIO_VIDEO_F_RESOURCE_GUEST_PAGES (0)] Guest pages can be used for
> > video + buffers.
> > +\end{description}
> > +
> > +\devicenormative{\subsubsection}{Feature bits}{Device Types / Video Device
> > / Feature bits} +
> > +The device MUST offer at least one of feature bits.
> > +
> > +\subsection{Device configuration layout}\label{sec:Device Types / Video
> > Device / Device configuration layout} +
> > +Video device configuration uses the following layout structure:
> > +
> > +\begin{lstlisting}
> > +struct virtio_video_config {
> > + le32 max_cap_len;
> > +};
> > +\end{lstlisting}
> > +
> > +\begin{description}
> > +\item[\field{max_cap_len}] defines the maximum length of a descriptor
> > + required to call VIRTIO_VIDEO_GET_CAPABILITY in bytes. The device
> > + MUST set this value.
> > +\end{description}
> > +
> > +\subsection{Device Initialization}\label{sec:Device Types / Video Device /
> > Device Initialization} +
> > +\devicenormative{\subsubsection}{Device Initialization}{Device Types /
> > Video Device / Device Initialization} +
> > +The driver SHOULD query device capability by using the
> > +VIRTIO_VIDEO_T_GET_CAPABILITY and use that information for the initial
> > +setup.
> > +
> > +\subsection{Device Operation}\label{sec:Device Types / Video Device /
> > Device Operation} +
> > +The driver allocates input and output buffers and queues the buffers
> > +to the device. The device performs operations on the buffers according
> > +to the function in question.
> > +
> > +\subsubsection{Device Operation: Create stream}
> > +
> > +To process buffers, the device needs to associate them with a certain
> > +video stream (essentially, a context). Streams are created by
> > +VIRTIO_VIDEO_T_STREAM_CREATE with a default set of parameters
> > +determined by the device.
> > +
> > +\subsubsection{Device Operation: Create buffers}
> > +
> > +Buffers are used to store the actual data as well as the relevant
> > +metadata. Scatter lists are supported, so the buffer doesn't need to
> > +be contiguous in guest physical memory.
> > +
> > +\begin{itemize*}
> > +\item Use VIRTIO_VIDEO_T_RESOURCE_CREATE to create a virtio video
> > + resource that is backed by a buffer allocated from the driver's
> > + memory.
> > +\item Use VIRTIO_VIDEO_T_RESOURCE_DESTROY to destroy a resource that
> > + is no longer needed.
> > +\end{itemize*}
> > +
> > +\subsubsection{Device Operation: Stream parameter control}
> > +
> > +\begin{itemize*}
> > +\item Use VIRTIO_VIDEO_T_GET_PARAMS to get the current stream parameters
> > for + input and output streams from the device.
> > +\item Use VIRTIO_VIDEO_T_SET_PARAMS to provide new stream parameters to the
> > + device.
> > +\item After setting stream parameters, the driver may issue
> > + VIRTIO_VIDEO_T_GET_PARAMS as some parameters of both input and output can
> > be + changed implicitly by the device during the set operation.
> > +\end{itemize*}
> > +
> > +\subsubsection{Device Operation: Process buffers}
> > +
> > +\begin{itemize*}
> > +\item If the function and the buffer type require so, write data to
> > +the buffer memory.
> > +\item Use VIRTIO_VIDEO_T_RESOURCE_QUEUE to queue the buffer for
> > +processing in the device.
> > +\item The request completes asynchronously when the device has
> > +finished with the buffer.
> > +\end{itemize*}
> > +
> > +\subsubsection{Device Operation: Buffer processing control}
> > +
> > +\begin{itemize*}
> > +\item Use VIRTIO_VIDEO_T_STREAM_DRAIN to ask the device to process and
> > + return all of the already queued buffers.
> > +\item Use VIRTIO_VIDEO_T_QUEUE_CLEAR to ask the device to return back
> > + already queued buffers from the input or the output queue. This also
> > + includes input or output buffers that can be currently owned by the
> > + device's processing pipeline.
> > +\end{itemize*}
> > +
> > +\subsubsection{Device Operation: Asynchronous events}
> > +
> > +While processing buffers, the device can send asynchronous event
> > +notifications to the driver. The behaviour depends on the exact
> > +stream. For example, the decoder device sends a resolution change
> > +event when it encounters new resolution metadata in the stream.
> > +
> > +\subsubsection{Device Operation: Request header}
> > +
> > +All requests and responses on the control virt queue have a fixed
> > +header using the following layout structure and definitions:
> > +
> > +\begin{lstlisting}
> > +enum virtio_video_ctrl_type {
> > + VIRTIO_VIDEO_CTRL_UNDEFINED = 0,
> > +
> > + /* request */
> > + VIRTIO_VIDEO_T_GET_CAPABILITY = 0x0100,
> > + VIRTIO_VIDEO_T_STREAM_CREATE,
> > + VIRTIO_VIDEO_T_STREAM_DESTROY,
> > + VIRTIO_VIDEO_T_STREAM_DRAIN,
> > + VIRTIO_VIDEO_T_RESOURCE_CREATE,
> > + VIRTIO_VIDEO_T_RESOURCE_DESTROY,
> > + VIRTIO_VIDEO_T_RESOURCE_QUEUE,
> > + VIRTIO_VIDEO_T_QUEUE_CLEAR,
> > + VIRTIO_VIDEO_T_SET_PARAMS,
> > + VIRTIO_VIDEO_T_GET_PARAMS,
> > +
> > + /* response */
> > + VIRTIO_VIDEO_S_OK = 0x0200,
> > + VIRTIO_VIDEO_S_OK_RESOURCE_QUEUE,
> > + VIRTIO_VIDEO_S_OK_GET_PARAMS,
> > +
> > + VIRTIO_VIDEO_S_ERR_UNSPEC = 0x0300,
> > + VIRTIO_VIDEO_S_ERR_OUT_OF_MEMORY,
> > + VIRTIO_VIDEO_S_ERR_INVALID_RESOURCE_ID,
> > + VIRTIO_VIDEO_S_ERR_INVALID_STREAM_ID,
> > + VIRTIO_VIDEO_S_ERR_INVALID_PARAMETER,
> > +};
> > +
> > +struct virtio_video_ctrl_hdr {
> > + le32 type;
> > + le32 stream_id;
> > + le32 len; /* Length of the structure in bytes. */
> > +};
> > +\end{lstlisting}
> > +
> > +\begin{description}
> > +\item[\field{type}] is the type of the driver request or the device
> > +response.
> > +\item[\field{stream_id}] specifies a target stream.
> > +\item[\field{len}] is the length of data in bytes, which includes
> > +length of the header.
> > +\end{description}
> > +
> > +\subsubsection{Device Operation: controlq}
> > +
> > +\begin{description}
> > +
> > +\item[VIRTIO_VIDEO_T_GET_CAPABILITY] Retrieve information about
> > +supported formats.
> > +
> > +The driver uses \field{struct virtio_video_get_capability} to send a
> > +query request.
> > +
> > +\begin{lstlisting}
> > +enum virtio_video_buf_type {
> > + VIRTIO_VIDEO_BUF_TYPE_INPUT,
> > + VIRTIO_VIDEO_BUF_TYPE_OUTPUT,
> > +};
> > +
> > +struct virtio_video_get_capability {
> > + struct virtio_video_ctrl_hdr hdr;
> > + enum virtio_video_buf_type buf_type;
> > +};
> > +\end{lstlisting}
> > +\begin{description}
> > +\item[\field{buf_type}] is the buffer type that the driver asks
> > +information about. The driver MUST set either
> > +\field{VIRTIO_VIDEO_BUF_TYPE_INPUT} or
> > \field{VIRTIO_VIDEO_BUF_TYPE_OUTPUT}. +\end{description}
> > +
> > +The device responds a capability by using \field{struct
> > +virtio_video_get_capability_resp}.
> > +\begin{lstlisting}
> > +enum virtio_video_format {
> > + VIRTIO_VIDEO_FORMAT_UNDEFINED = 0,
> > + /* Raw formats */
> > + VIRTIO_VIDEO_FORMAT_NV12 = 1,
> > + VIRTIO_VIDEO_FORMAT_YUV420,
> > + VIRTIO_VIDEO_FORMAT_YVU420,
> > +
> > + /* Compressed formats */
> > + VIRTIO_VIDEO_FORMAT_H264 = 0x1001,
> > + VIRTIO_VIDEO_FORMAT_VP8 = 0x1002,
> > + VIRTIO_VIDEO_FORMAT_VP9 = 0x1003,
> > +};
> > +
> > +enum virtio_video_profile {
> > + VIRTIO_VIDEO_PROFILE_UNDEFINED = 0,
> > +
> > + /* H.264 */
> > + VIRTIO_VIDEO_PROFILE_H264_MIN = 0x100,
> > + VIRTIO_VIDEO_PROFILE_H264_BASELINE =
> > VIRTIO_VIDEO_PROFILE_H264_BASELINE, +
> > VIRTIO_VIDEO_PROFILE_H264_MAIN,
> > + VIRTIO_VIDEO_PROFILE_H264_EXTENDED,
> > + VIRTIO_VIDEO_PROFILE_H264_HIGH,
> > + VIRTIO_VIDEO_PROFILE_H264_HIGH10PROFILE,
> > + VIRTIO_VIDEO_PROFILE_H264_HIGH422PROFILE,
> > + VIRTIO_VIDEO_PROFILE_H264_HIGH444PREDICTIVEPROFILE,
> > + VIRTIO_VIDEO_PROFILE_H264_SCALABLEBASELINE,
> > + VIRTIO_VIDEO_PROFILE_H264_SCALABLEHIGH,
> > + VIRTIO_VIDEO_PROFILE_H264_STEREOHIGH,
> > + VIRTIO_VIDEO_PROFILE_H264_MULTIVIEWHIGH,
> > + VIRTIO_VIDEO_PROFILE_H264_MAX =
> > VIRTIO_VIDEO_PROFILE_H264_MULTIVIEWHIGH, +
> > + /* VP8 */
> > + VIRTIO_VIDEO_PROFILE_VP8_MIN = 0x200,
> > + VIRTIO_VIDEO_PROFILE_VP8_ANY = VIRTIO_VIDEO_PROFILE_VP8_MIN,
> > + VIRTIO_VIDEO_PROFILE_VP8_MAX = VIRTIO_VIDEO_PROFILE_VP8_ANY,
> > +
> > + /* VP9 */
> > + VIRTIO_VIDEO_PROFILE_VP9_MIN = 0x300,
> > + VIRTIO_VIDEO_PROFILE_VP9_PROFILE0 = VIRTIO_VIDEO_PROFILE_VP9_MIN,
> > + VIRTIO_VIDEO_PROFILE_VP9_PROFILE1,
> > + VIRTIO_VIDEO_PROFILE_VP9_PROFILE2,
> > + VIRTIO_VIDEO_PROFILE_VP9_PROFILE3,
> > + VIRTIO_VIDEO_PROFILE_VP9_MAX = VIRTIO_VIDEO_PROFILE_VP9_PROFILE3,
> > +};
> > +
> > +struct virtio_video_format_range {
> > + le32 min;
> > + le32 max;
> > + le32 step;
> > + u8 paddings[4];
> > +};
> > +
> > +struct virtio_video_format_desc {
> > + le32 format; /* One of VIRTIO_VIDEO_FORMAT_* types */
> > + le32 profile; /* One of VIRTIO_VIDEO_PROFILE_* types */
> > + le64 mask;
> > + struct virtio_video_format_range width;
> > + struct virtio_video_format_range height;
> > + le32 num_rates;
> > + u8 padding[4];
> > + /* Followed by struct virtio_video_frame_rate frame_rates[] */
> > +};
> > +
> > +struct virtio_video_get_capability_resp {
> > + struct virtio_video_ctrl_hdr hdr;
> > + le32 num_descs;
> > + /* Followed by struct virtio_video_format_desc desc[] */
> > +};
> > +\end{lstlisting}
> > +
> > +The format description \field{struct virtio_video_format_desc}
> > +includes the following fields:
> > +\begin{description}
> > +\item[\field{format}] specifies an image format. The device MUST set one
> > + of \field{enum virtio_video_format}.
> > +\item[\field{profile}] specifies a profile of the compressed image format
> > + specified in \field{format}. The driver SHOULD ignore this value if
> > + \field{format} is a raw format.
>
> So how should this be used? The spec does not define any way to set profile for
> the device. It is very important for encoder.
>

Thank you for pointing this.
These points are overlooked, as I didn't care about encoder usage enough.

After thinking it again, I think it's not a very good idea to include
supported profiles and levels in a struct for capability.
This is because these values are available only for limited number of formats.
Also, it's true that we need to have a way to set these values as
Dmitry pointed.

Instead, it would make more sense to have additional three types of
controls for profiles, levels, and bitrates:
(1) QUERY_CONTROL: Query values supported by the device
(2) GET_CONTROL: Read a value that is set in the device
(3) SET_CONTROL: Set a value in the device

These operations are similar to V4L2 controls.
(1), (2) and (3) would correspond VIDIOC_QUERY{CTRL,MENU}, S_CTRL, and
G_CTRL in V4L2, respectively.
Also, (3) would be similar to enum virtio_video_control_type in the
virtio-video v1 driver implementation in
https://markmail.org/message/dwghwdqsbl3gsjxu .

For QUERY_CONTROL, my idea is like this:

enum virtio_video_control_type {
VIRTIO_VIDEO_CONTROL_UNDEFINED = 0,

VIRTIO_VIDEO_CONTROL_BITRATE = 0x100,
VIRTIO_VIDEO_CONTROL_PROFILE,
VIRTIO_VIDEO_CONTROL_LEVEL,
};

struct virtio_video_query_control {
struct virtio_video_ctrl_hdr hdr;
le32 control; /* One of VIRTIO_VIDEO_CONTROL_* types */
le32 length;
/* Followed by additional data.
* If |control| is VIRTIO_VIDEO_CONTROL_PROFILE,
* the device must pass a codec format like H264 or VP9.
* The requred data must be defined in the specification.
*/
};

struct virtio_video_query_control_resp {
struct virtio_video_ctrl_hdr hdr;
le32 length;
u8 padding[4];
/* Followed by data corresponds to the specified control.
* The type of data must be defined in the spec.
* For example, if the driver queries profiles, this part should be
* an array of supported profiles of a given format.
*/
};

WDYT?

> Also, shouldn't the profile come together with level? Would make sense for
> encoders.

Yeah. So, in the above idea of QUERY_CONTROL, profile should be
required when querying supported levels.

>
> > +\item[\field{mask}] is a bitset that represents the supported
> > + combination of input and output format. If \textit{i}-th bit is set
> > + in \field{mask} of \textit{j}-th \field{struct
> > + virtio_video_format_desc} for input, the device supports encoding or
> > + decoding from the \textit{j}-th input format to \textit{i}-th output
> > + format.
> > +\item[\field{width, height}] represents a range of resolutions
> > + supported by the device. If its \field{step} is not applicable, its
> > + \field{min} is equal to its \field{max}.
> > +\item[\field{num_rates}] is the length of an array \field{frame_rates}. In
> > case of decoder, the driver SHOULD ignore this value.
> > +\item[\field{frame_rates}] is an array of supported frame rates.
> > +\end{description}
> > +
>
> I'd guess frame rates depend on the resolution as well. This dependency was
> clear in the v1 spec, but in the v2 there is no dependency anymore. I think we
> need to update this.

That's a good point. I missed that dependency when updating the structures.
So, let me update the structs like the following:

struct virtio_video_format_frame {
struct virtio_video_format_range width;
struct virtio_video_format_range height;
le32 num_rates;
u8 padding[4];
/* Followed by struct virtio_video_format_range frame_rates[] */
};

struct virtio_video_format_desc {
le64 mask;
le32 format; /* One of VIRTIO_VIDEO_FORMAT_* types */
le32 planes_layout; /* See the thread [v2 0/1] */
le32 num_frames;
u8 padding[4];
/* Followed by struct virtio_video_format_frame frames[] */
};

Best regards,
Keiichi.

>
> Best regards,
> Dmitry.
>
> > +\item[VIRTIO_VIDEO_T_STREAM_CREATE] create a video stream (context)
> > + within the device.
> > +
> > +\begin{lstlisting}
> > +enum virtio_video_mem_type {
> > + VIRTIO_VIDEO_MEM_TYPE_GUEST_PAGES,
> > +};
> > +
> > +struct virtio_video_stream_create {
> > + struct virtio_video_ctrl_hdr hdr;
> > + le32 in_mem_type; /* One of VIRTIO_VIDEO_MEM_TYPE_* types */
> > + le32 out_mem_type; /* One of VIRTIO_VIDEO_MEM_TYPE_* types */
> > + char debug_name[64];
> > +};
> > +\end{lstlisting}
> > +
> > +\begin{description}
> > +\item[\field{in_mem_type}] is a type of buffer management for input
> > +buffers. The driver MUST set a value in \field{enum
> > +virtio_video_mem_type}.
> > +\item[\field{out_mem_type}] is a type of buffer management for output
> > +buffers. The driver MUST set a value in \field{enum
> > +virtio_video_mem_type}.
> > +\item[\field{debug_name}] is a text string for a debug purpose.
> > +\end{description}
> > +
> > +\item[VIRTIO_VIDEO_T_STREAM_DESTROY] destroy a video stream (context)
> > + within the device.
> > +
> > +\begin{lstlisting}
> > +struct virtio_video_stream_destroy {
> > + struct virtio_video_ctrl_hdr hdr;
> > +};
> > +\end{lstlisting}
> > +
> > +\item[VIRTIO_VIDEO_T_STREAM_DRAIN] ask the device to push all the
> > + queued buffers through the pipeline.
> > +
> > +\begin{lstlisting}
> > +struct virtio_video_stream_drain {
> > + struct virtio_video_ctrl_hdr hdr;
> > +};
> > +\end{lstlisting}
> > +
> > +\item[VIRTIO_VIDEO_T_RESOURCE_CREATE] create a resource descriptor
> > + within the device.
> > +
> > +\begin{lstlisting}
> > +struct virtio_video_mem_entry {
> > + le64 addr;
> > + le32 length;
> > + u8 padding[4];
> > +};
> > +
> > +struct virtio_video_resource_create {
> > + struct virtio_video_ctrl_hdr hdr;
> > + le32 resource_id;
> > + le32 nr_entries;
> > +};
> > +\end{lstlisting}
> > +
> > +\begin{description}
> > +\item[\field{resource_id}] internal id of the resource.
> > +\item[\field{nr_entries}] number of \field{struct
> > + virtio_video_mem_entry} memory entries.
> > +\end{description}
> > +
> > +\item[VIRTIO_VIDEO_T_RESOURCE_DESTROY] destroy a resource descriptor
> > + within the device.
> > +
> > +\begin{lstlisting}
> > +struct virtio_video_resource_destroy {
> > + struct virtio_video_ctrl_hdr hdr;
> > + le32 resource_id;
> > + u8 padding[4];
> > +};
> > +\end{lstlisting}
> > +
> > +\begin{description}
> > +\item[\field{resource_id}] internal id of the resource.
> > +\end{description}
> > +
> > +\item[VIRTIO_VIDEO_T_RESOURCE_QUEUE] Add a buffer to the device's
> > +queue.
> > +
> > +\begin{lstlisting}
> > +#define VIRTIO_VIDEO_MAX_PLANES 8
> > +
> > +struct virtio_video_resource_queue {
> > + struct virtio_video_ctrl_hdr hdr;
> > + le32 buf_type;
> > + le32 resource_id;
> > + le64 timestamp;
> > + le32 nr_data_size;
> > + le32 data_size[VIRTIO_VIDEO_MAX_PLANES];
> > +};
> > +\end{lstlisting}
> > +
> > +\begin{description}
> > +\item[\field{buf_type}] buf_type of the .
> > +\item[\field{resource_id}] internal id of the resource.
> > +\item[\field{timestamp}] an abstract sequence counter that can be used
> > + for synchronisation.
> > +\item[\field{nr_data_size}] number of \field{data_size} entries.
> > +\item[\field{data_size}] number of data bytes within a plane.
> > +\end{description}
> > +
> > +\begin{lstlisting}
> > +enum virtio_video_buffer_flag {
> > + VIRTIO_VIDEO_BUFFER_F_ERR = 0x0001,
> > + VIRTIO_VIDEO_BUFFER_F_EOS = 0x0002,
> > + /* Encoder only */
> > + VIRTIO_VIDEO_BUFFER_IFRAME = 0x0004,
> > + VIRTIO_VIDEO_BUFFER_PFRAME = 0x0008,
> > + VIRTIO_VIDEO_BUFFER_BFRAME = 0x0010,
> > +};
> > +
> > +struct virtio_video_resource_queue_resp {
> > + struct virtio_video_ctrl_hdr hdr;
> > + le64 timestamp;
> > + le32 flags; /* One of VIRTIO_VIDEO_BUFFER_* flags */
> > + le32 size; /* Encoded size */
> > +};
> > +\end{lstlisting}
> > +
> > +\begin{description}
> > +\item[\field{timestamp}] an abstract sequence counter that can be used
> > + for synchronisation.
> > +\item[\field{flags}] mark specific buffers in the sequence.
> > +\item[\field{size}] data size in the buffer (encoder only).
> > +\end{description}
> > +
> > +The device sends a response to the queue request asynchronously when
> > +it has finished processing the buffer.
> > +
> > +The device SHOULD mark a buffer that triggered a processing error with
> > +the VIRTIO_VIDEO_BUFFER_F_ERR flag.
> > +
> > +The device MUST mark the last buffer with the
> > +VIRTIO_VIDEO_BUFFER_F_EOS flag to denote completion of the drain
> > +sequence.
> > +
> > +In case of encoder, to denote a particular frame type the devie MUST
> > +mark the respective buffer with VIRTIO_VIDEO_BUFFER_IFRAME,
> > +VIRTIO_VIDEO_BUFFER_PFRAME, VIRTIO_VIDEO_BUFFER_BFRAME.
> > +
> > +\item[VIRTIO_VIDEO_T_RESOURCE_QUEUE_CLEAR] Return already queued
> > + buffers back from the input or the output queue of the device. The
> > + device SHOULD return all of the buffers from the respective queue as
> > + soon as possible without pushing the buffers through the processing
> > + pipeline.
> > +
> > +\begin{lstlisting}
> > +struct virtio_video_queue_clear {
> > + struct virtio_video_ctrl_hdr hdr;
> > + le32 buf_type;
> > + u8 padding[4];
> > +};
> > +\end{lstlisting}
> > +
> > +\begin{description}
> > +\item[\field{buf_type}] buffer type.
> > +\end{description}
> > +
> > +\item[VIRTIO_VIDEO_T_GET_PARAMS] Get parameters of the input or the
> > + output of a stream.
> > +
> > +\begin{lstlisting}
> > +struct virtio_video_plane_format {
> > + le32 plane_size;
> > + le32 stride;
> > + u8 padding[4];
> > +};
> > +\end{lstlisting}
> > +
> > +\begin{description}
> > +\item[\field{plane_size}] size of the plane in bytes.
> > +\item[\field{stride}] stride used for the plane in bytes.
> > +\end{description}
> > +
> > +\begin{lstlisting}
> > +struct virtio_video_params {
> > + le32 buf_type; /* One of VIRTIO_VIDEO_BUF_TYPE_* types */
> > + le32 fourcc; /* One of VIRTIO_VIDEO_FOURCC_* types */
> > + le32 frame_width;
> > + le32 frame_height;
> > + le32 min_buffers;
> > + le32 max_buffers;
> > + le32 frame_rate;
> > + struct virtio_video_crop {
> > + le32 left;
> > + le32 top;
> > + le32 width;
> > + le32 height;
> > + } crop;
> > + le32 num_planes;
> > + struct virtio_video_plane_format
> > plane_formats[VIRTIO_VIDEO_MAX_PLANES]; +};
> > +\end{lstlisting}
> > +
> > +\begin{description}
> > +\item[\field{frame_width}] the value to get/set.
> > +\item[\field{frame_height}] the value to get/set.
> > +\item[\field{pixel_format}] the value to get/set.
> > +\item[\field{min_buffers}] minimum buffers required to handle the
> > + format (r/o).
> > +\item[\field{max_buffers}] maximum buffers required to handle the
> > + format (r/o).
> > +\item[\field{frame_rate}] the value to get/set.
> > +\item[\field{crop}] cropping (composing) rectangle.
> > +\item[\field{num_planes}] number of planes used to store pixel data
> > +(r/o).
> > +\item[\field{plane_formats}] description of each plane.
> > +\end{description}
> > +
> > +\begin{lstlisting}
> > +struct virtio_video_get_params {
> > + struct virtio_video_ctrl_hdr hdr;
> > + le32 buf_type; /* One of VIRTIO_VIDEO_BUF_TYPE_* types */
> > +};
> > +
> > +struct virtio_video_get_params_resp {
> > + struct virtio_video_ctrl_hdr hdr;
> > + struct virtio_video_params params;
> > +};
> > +\end{lstlisting}
> > +
> > +\begin{description}
> > +\item[\field{buf_type}] buffer type.
> > +\item[\field{params}] parameter values.
> > +\end{description}
> > +
> > +\item[VIRTIO_VIDEO_T_SET_PARAMS] Change parameters of a stream.
> > +
> > +
> > +\begin{lstlisting}
> > +struct virtio_video_set_params {
> > + struct virtio_video_ctrl_hdr hdr;
> > + struct virtio_video_params params;
> > +};
> > +\end{lstlisting}
> > +
> > +\begin{description}
> > +\item[\field{params}] parameters to set.
> > +\end{description}
> > +
> > +Setting stream parameters might have side effects within the device.
> > +For example, the device MAY perform alignment of width and height,
> > +change the number of planes it uses for the format, or do whatever
> > +changes that are required to continue normal operation using the
> > +updated parameters. It is up to the driver to check the parameter set
> > +after the VIRTIO_VIDEO_T_SET_PARAMS request has been issued.
> > +
> > +\end{description}
> > +
> > +\subsubsection{Device Operation: eventq}
> > +
> > +The device can report events on the event queue. The driver initially
> > +populates the queue with device-writeable buffers. When the device
> > +needs to report an event, it fills a buffer and notifies the driver.
> > +The driver consumes the report and adds a new buffer to the virtqueue.
> > +
> > +\begin{lstlisting}
> > +enum virtio_video_event_type {
> > + VIRTIO_VIDEO_EVENT_T_UNDEFINED = 0,
> > + /* For all functions */
> > + VIRTIO_VIDEO_EVENT_T_ERROR_UNSPEC = 0x0100,
> > + /* For decoder only */
> > + VIRTIO_VIDEO_EVENT_T_DECODER_RESOLUTION_CHANGED = 0x0200,
> > +};
> > +
> > +struct virtio_video_event {
> > + le32 event_type; /* One of VIRTIO_VIDEO_EVENT_T_* types */
> > + le32 stream_id;
> > + u8 padding[4];
> > +};
> > +\end{lstlisting}
> > +
> > +\begin{description}
> > +\item[\field{event_type}] type of the triggered event .
> > +\item[\field{stream_id}] id of the source stream.
> > +\end{description}
> > +
> > +The device MUST send VIRTIO_VIDEO_EVENT_T_DECODER_RESOLUTION_CHANGED
> > +whenever it encounters new resolution data in the stream. This
> > +includes the case of the initial device configuration after metadata
> > +has been parsed and the case of dynamic resolution change.
>
>