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

[Keiichi Watanabe <keiichiw@chromium.org>]

Hi Frediano,
Thanks for reviewing!

On Thu, Dec 19, 2019 at 2:29 AM Frediano Ziglio <fziglio@redhat.com> 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.
>
> I suppose is implicit that it's the size of the container structure.
>

You're right. All struct except virtio_video_get_capability_resp have
fixed size and virtio_video_get_capability_resp has num_descs. So, no
need to have len.
Let me remove this in the next iteration.


> > +\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;
>
> Here you used an enumeration but later you are using just le32 type
> with a comment. Why this difference?

No difference. I will change this to use le32 since virtio-gpu's spec does so.

>
> > +};
> > +\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,
>
> Really minor: maybe you want to insert an empty line to be coherent
> with other enumerations?

Yes. Thanks.

>
> > +        /* 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,
>
> Maybe you want
>
> VIRTIO_VIDEO_PROFILE_H264_BASELINE = VIRTIO_VIDEO_PROFILE_H264_MIN,
>
> like others?

Thanks for catching this. I think we can find this kind of errors once
we update the driver implementation.

>
> > +        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];
>
> Here you padded at 8-byte like many other structures but not for
> virtio_video_ctrl_hdr. Is this expected?

I padded here for 64-bits alignment. So, I should have padded for
ctrl_hdr as you said. But, no need anymore as we will remove |len|
from the struct as you suggested above:)

>
> > +};
> > +
> > +struct virtio_video_format_desc {
> > +        le32 format;  /* One of VIRTIO_VIDEO_FORMAT_* types */
> > +        le32 profile; /* One of VIRTIO_VIDEO_PROFILE_* types */
> > +        le64 mask;
>
> This will limit the formats to 64 while "num_descs" below is a
> 32 bit.

It's my intention. I will explicitly write that "num_desc" must not exceed 64.
I guess 64 is big enough as a number of supported input/output format
and couldn't find a better idea to represent this bipartite graph. If
you have another idea, please let me hear.

>
> > +        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.
>
> Why not documenting that MUST be VIRTIO_VIDEO_PROFILE_UNDEFINED for
> raw formats so the field could be extended in the future?

Sounds good. Will do.

>
> > +\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.
>
> I suppose here we are talking about bitrates, right? Could be confused by
> FPS.

Nope. This is for frame rates or frame intervals. In V4L2 driver, the
values will be used for VIDIOC_ENUM_FRAMEINTERVALS ioctl.
(Dmitry, please correct me if I am wrong)

>
> > +\end{description}
> > +
> > +\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];
> > +};
>
> This structure has a size not multiple of 8-bytes. Not an issue, but
> the same apply to other structures that instead are padded to 8-byte size.

It's my fault. I tried to add paddings to make all structs' size
multiple of 8-bytes, I overlooked some.

>
> > +\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.
>
> Must be NUL-terminated ? UTF-8 ?

Yeah, I will add a description similar to one for "tag" in virtio_fs_config.

>
> > +\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.
>
> Is it input or output?

Will add a field for it.

>
> > +\item[\field{nr_entries}] number of \field{struct
> > +  virtio_video_mem_entry} memory entries.
>
> I suppose that the structure is followed by an array of
> virtio_video_mem_entry after a padding of 4-bytes for
> alignment.
>
> > +\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];
>
> Is this padding for future extensions?

Nope, it's mistake. When I was editing structs, I forgot to add/remove
padding. I hope we will not have such mistakes after we have an
updated driver implementation.

>
> > +};
> > +\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;
>
> I suppose you would like this field aligned to avoid
> hidden paddings.

Thanks.

Best regards,
Keiichi

>
> > +        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}
> > +
> ... omissis ...
> > --
> > 2.24.1.735.g03f4e72817-goog
> >
> >
>
> Frediano
>