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Subject: Re: [virtio-dev] [PATCH] Add virtio gpu device specification.
On 07/03/18 02:15, Michael S. Tsirkin wrote:
> On Wed, Jun 27, 2018 at 08:15:25AM +0200, Gerd Hoffmann wrote:
>> Support for 2d mode (3d/virgl mode is not covered by this patch) has
>> been added to the linux kernel version 4.2 and to qemu version 2.4.
>>
>> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
>
> No comments so far, as Gerd seems to be the only one with both
> understanding the field and willing to contribute to the spec, I will
> start voting in a couple of days unless there's interest from TC members
> in working on this.
I remember that, when I was writing the OVMF guest driver against this
spec, I found a typo. I don't remember if I notified Gerd at the time. Hmmm.
... Yup, found it: we have an enum constant called
VIRTIO_GPU_CMD_TRANSFER_TO_HOST_2D, and there is one reference by that
name in the text. However, there are three more references to the same
thing, but under a (likely obsolete?) name:
VIRTIO_GPU_CMD_TRANSFER_SEND_2D. Those should be updated.
Gerd, I'm sorry about not raising this earlier. (I'm also sorry about
missing the posting on virtio-dev; I've only learned about it today from
a different email.)
I have no other comments; the spec was sufficient to write the OVMF
guest driver against the QEMU device model.
Thanks
Laszlo
>> ---
>> content.tex | 2 +
>> virtio-gpu.tex | 481 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>> 2 files changed, 483 insertions(+)
>> create mode 100644 virtio-gpu.tex
>>
>> diff --git a/content.tex b/content.tex
>> index be1823431d..d41c2f8d76 100644
>> --- a/content.tex
>> +++ b/content.tex
>> @@ -5325,6 +5325,8 @@ descriptor for the \field{sense_len}, \field{residual},
>> \field{status_qualifier}, \field{status}, \field{response} and
>> \field{sense} fields.
>>
>> +\input{virtio-gpu.tex}
>> +
>> \chapter{Reserved Feature Bits}\label{sec:Reserved Feature Bits}
>>
>> Currently these device-independent feature bits defined:
>> diff --git a/virtio-gpu.tex b/virtio-gpu.tex
>> new file mode 100644
>> index 0000000000..34cf493bbc
>> --- /dev/null
>> +++ b/virtio-gpu.tex
>> @@ -0,0 +1,481 @@
>> +\section{GPU Device}\label{sec:Device Types / GPU Device}
>> +
>> +virtio-gpu is a virtio based graphics adapter. It can operate in 2D
>> +mode and in 3D (virgl) mode. 3D mode will offload rendering ops to
>> +the host gpu and therefore requires a gpu with 3D support on the host
>> +machine.
>> +
>> +3D mode is not covered (yet) in this specification, even though it is
>> +mentioned here and there due to some details of the virtual hardware
>> +being designed with 3D mode in mind.
>> +
>> +In 2D mode the virtio-gpu device provides support for ARGB Hardware
>> +cursors and multiple scanouts (aka heads).
>> +
>> +\subsection{Device ID}\label{sec:Device Types / GPU Device / Device ID}
>> +
>> +16
>> +
>> +\subsection{Virtqueues}\label{sec:Device Types / GPU Device / Virtqueues}
>> +
>> +\begin{description}
>> +\item[0] controlq - queue for sending control commands
>> +\item[1] cursorq - queue for sending cursor updates
>> +\end{description}
>> +
>> +Both queues have the same format. Each request and each response have
>> +a fixed header, followed by command specific data fields. The
>> +separate cursor queue is the "fast track" for cursor commands
>> +(VIRTIO_GPU_CMD_UPDATE_CURSOR and VIRTIO_GPU_CMD_MOVE_CURSOR), so they
>> +go though without being delayed by time-consuming commands in the
>> +control queue.
>> +
>> +\subsection{Feature bits}\label{sec:Device Types / GPU Device / Feature bits}
>> +
>> +\begin{description}
>> +\item[VIRTIO_GPU_F_VIRGL (0)] virgl 3D mode is supported.
>> +\end{description}
>> +
>> +\subsection{Device configuration layout}\label{sec:Device Types / GPU Device / Device configuration layout}
>> +
>> +\begin{lstlisting}
>> +#define VIRTIO_GPU_EVENT_DISPLAY (1 << 0)
>> +
>> +struct virtio_gpu_config {
>> + le32 events_read;
>> + le32 events_clear;
>> + le32 num_scanouts;
>> + le32 reserved;
>> +}
>> +\end{lstlisting}
>> +
>> +\subsubsection{Device configuration fields}
>> +
>> +\begin{description}
>> +\item[\field{events_read}] signals pending events to the driver. The
>> + driver MUST NOT write to this field.
>> +\item[\field{events_clear}] clears pending events in the device.
>> + Writing a '1' into a bit will clear the corresponding bit in
>> + \field{events_read}, mimicking write-to-clear behavior.
>> +\item[\field{num_scanouts}] specifies the maximum number of scanouts
>> + supported by the device. Minimum value is 1, maximum value is 16.
>> +\end{description}
>> +
>> +\subsubsection{Events}
>> +
>> +\begin{description}
>> +\item[VIRTIO_GPU_EVENT_DISPLAY] Display configuration has changed.
>> + The driver SHOULD use the VIRTIO_GPU_CMD_GET_DISPLAY_INFO command to
>> + fetch the information from the device.
>> +\end{description}
>> +
>> +\devicenormative{\subsection}{Device Initialization}{Device Types / GPU Device / Device Initialization}
>> +
>> +The driver SHOULD query the display information from the device using
>> +the VIRTIO_GPU_CMD_GET_DISPLAY_INFO command and use that information
>> +for the initial scanout setup. In case no information is available or
>> +all displays are disabled the driver MAY choose to use a fallback,
>> +such as 1024x768 at display 0.
>> +
>> +\subsection{Device Operation}\label{sec:Device Types / GPU Device / Device Operation}
>> +
>> +The virtio-gpu is based around the concept of resources private to the
>> +host, the guest must DMA transfer into these resources. This is a
>> +design requirement in order to interface with future 3D rendering. In
>> +the unaccelerated 2D mode there is no support for DMA transfers from
>> +resources, just to them.
>> +
>> +Resources are initially simple 2D resources, consisting of a width,
>> +height and format along with an identifier. The guest must then attach
>> +backing store to the resources in order for DMA transfers to
>> +work. This is like a GART in a real GPU.
>> +
>> +\subsubsection{Device Operation: Create a framebuffer and configure scanout}
>> +
>> +\begin{itemize*}
>> +\item Create a host resource using VIRTIO_GPU_CMD_RESOURCE_CREATE_2D.
>> +\item Allocate a framebuffer from guest ram, and attach it as backing
>> + storage to the resource just created, using
>> + VIRTIO_GPU_CMD_RESOURCE_ATTACH_BACKING. Scatter lists are
>> + supported, so the framebuffer doesn't need to be contignous in guest
>> + physical memory.
>> +\item Use VIRTIO_GPU_CMD_SET_SCANOUT to link the framebuffer to
>> + a display scanout.
>> +\end{itemize*}
>> +
>> +\subsubsection{Device Operation: Update a framebuffer and scanout}
>> +
>> +\begin{itemize*}
>> +\item Render to your framebuffer memory.
>> +\item Use VIRTIO_GPU_CMD_TRANSFER_SEND_2D to update the host resource
>> + from guest memory.
>> +\item Use VIRTIO_GPU_CMD_RESOURCE_FLUSH to flush the updated resource
>> + to the display.
>> +\end{itemize*}
>> +
>> +\subsubsection{Device Operation: Using pageflip}
>> +
>> +It is possible to create multiple framebuffers, flip between them
>> +using VIRTIO_GPU_CMD_SET_SCANOUT and VIRTIO_GPU_CMD_RESOURCE_FLUSH,
>> +and update the invisible framebuffer using
>> +VIRTIO_GPU_CMD_TRANSFER_SEND_2D.
>> +
>> +\subsubsection{Device Operation: Multihead setup}
>> +
>> +In case two or more displays are present there are different ways to
>> +configure things:
>> +
>> +\begin{itemize*}
>> +\item Create a single framebuffer, link it to all displays
>> + (mirroring).
>> +\item Create an framebuffer for each display.
>> +\item Create one big framebuffer, configure scanouts to display a
>> + different rectangle of that framebuffer each.
>> +\end{itemize*}
>> +
>> +\devicenormative{\subsubsection}{Device Operation: Command lifecycle and fencing}{Device Types / GPU Device / Device Operation / Device Operation: Command lifecycle and fencing}
>> +
>> +The device MAY process controlq commands asyncronously and return them
>> +to the driver before the processing is complete. If the driver needs
>> +to know when the processing is finished it can set the
>> +VIRTIO_GPU_FLAG_FENCE flag in the request. The device MUST finish the
>> +processing before returning the command then.
>> +
>> +Note: current qemu implementation does asyncrounous processing only in
>> +3d mode, when offloading the processing to the host gpu.
>> +
>> +\subsubsection{Device Operation: Configure mouse cursor}
>> +
>> +The mouse cursor image is a normal resource, except that it must be
>> +64x64 in size. The driver MUST create and populate the resource
>> +(using the usual VIRTIO_GPU_CMD_RESOURCE_CREATE_2D,
>> +VIRTIO_GPU_CMD_RESOURCE_ATTACH_BACKING and
>> +VIRTIO_GPU_CMD_TRANSFER_SEND_2D controlq commands) and make sure they
>> +are completed (using VIRTIO_GPU_FLAG_FENCE).
>> +
>> +Then VIRTIO_GPU_CMD_UPDATE_CURSOR can be sent to the cursorq to set
>> +the pointer shape and position. To move the pointer without updating
>> +the shape use VIRTIO_GPU_CMD_MOVE_CURSOR instead.
>> +
>> +\subsubsection{Device Operation: Request header}\label{sec:Device Types / GPU Device / Device Operation / Device Operation: Request header}
>> +
>> +\begin{lstlisting}
>> +enum virtio_gpu_ctrl_type {
>> +
>> + /* 2d commands */
>> + VIRTIO_GPU_CMD_GET_DISPLAY_INFO = 0x0100,
>> + VIRTIO_GPU_CMD_RESOURCE_CREATE_2D,
>> + VIRTIO_GPU_CMD_RESOURCE_UNREF,
>> + VIRTIO_GPU_CMD_SET_SCANOUT,
>> + VIRTIO_GPU_CMD_RESOURCE_FLUSH,
>> + VIRTIO_GPU_CMD_TRANSFER_TO_HOST_2D,
>> + VIRTIO_GPU_CMD_RESOURCE_ATTACH_BACKING,
>> + VIRTIO_GPU_CMD_RESOURCE_DETACH_BACKING,
>> +
>> + /* cursor commands */
>> + VIRTIO_GPU_CMD_UPDATE_CURSOR = 0x0300,
>> + VIRTIO_GPU_CMD_MOVE_CURSOR,
>> +
>> + /* success responses */
>> + VIRTIO_GPU_RESP_OK_NODATA = 0x1100,
>> + VIRTIO_GPU_RESP_OK_DISPLAY_INFO,
>> +
>> + /* error responses */
>> + VIRTIO_GPU_RESP_ERR_UNSPEC = 0x1200,
>> + VIRTIO_GPU_RESP_ERR_OUT_OF_MEMORY,
>> + VIRTIO_GPU_RESP_ERR_INVALID_SCANOUT_ID,
>> + VIRTIO_GPU_RESP_ERR_INVALID_RESOURCE_ID,
>> + VIRTIO_GPU_RESP_ERR_INVALID_CONTEXT_ID,
>> + VIRTIO_GPU_RESP_ERR_INVALID_PARAMETER,
>> +};
>> +
>> +#define VIRTIO_GPU_FLAG_FENCE (1 << 0)
>> +
>> +struct virtio_gpu_ctrl_hdr {
>> + le32 type;
>> + le32 flags;
>> + le64 fence_id;
>> + le32 ctx_id;
>> + le32 padding;
>> +};
>> +\end{lstlisting}
>> +
>> +All requests and responses on the virt queues have the fixed header
>> +\field{struct virtio_gpu_ctrl_hdr}.
>> +
>> +\begin{description}
>> +\item[\field{type}] specifies the type of the driver request
>> + (VIRTIO_GPU_CMD_*) or device response (VIRTIO_GPU_RESP_*).
>> +\item[\field{flags}] request / response flags.
>> +\item[\field{fence_id}] If the driver sets the VIRTIO_GPU_FLAG_FENCE
>> + bit in the request \field{flags} field the device MUST:
>> + \begin{itemize*}
>> + \item set VIRTIO_GPU_FLAG_FENCE bit in the response,
>> + \item copy the content of the \field{fence_id} field from the
>> + request to the response, and
>> + \item send the response only after command processing is complete.
>> + \end{itemize*}
>> +\item[\field{ctx_id}] Rendering context (used in 3D mode only).
>> +\end{description}
>> +
>> +On success the device will return VIRTIO_GPU_RESP_OK_NODATA in
>> +case there is no payload. Otherwise the \field{type} field will
>> +indicate the kind of payload.
>> +
>> +On error the device will return one of the
>> +VIRTIO_GPU_RESP_ERR_* error codes.
>> +
>> +\subsubsection{Device Operation: controlq}\label{sec:Device Types / GPU Device / Device Operation / Device Operation: controlq}
>> +
>> +For any coordinates given 0,0 is top left, larger x moves right,
>> +larger y moves down.
>> +
>> +\begin{description}
>> +
>> +\item[VIRTIO_GPU_CMD_GET_DISPLAY_INFO] Retrieve the current output
>> + configuration. No request data (just bare \field{struct
>> + virtio_gpu_ctrl_hdr}). Response type is
>> + VIRTIO_GPU_RESP_OK_DISPLAY_INFO, response data is \field{struct
>> + virtio_gpu_resp_display_info}.
>> +
>> +\begin{lstlisting}
>> +#define VIRTIO_GPU_MAX_SCANOUTS 16
>> +
>> +struct virtio_gpu_rect {
>> + le32 x;
>> + le32 y;
>> + le32 width;
>> + le32 height;
>> +};
>> +
>> +struct virtio_gpu_resp_display_info {
>> + struct virtio_gpu_ctrl_hdr hdr;
>> + struct virtio_gpu_display_one {
>> + struct virtio_gpu_rect r;
>> + le32 enabled;
>> + le32 flags;
>> + } pmodes[VIRTIO_GPU_MAX_SCANOUTS];
>> +};
>> +\end{lstlisting}
>> +
>> +The response contains a list of per-scanout information. The info
>> +contains whether the scanout is enabled and what its preferred
>> +position and size is.
>> +
>> +The size (fields \field{width} and \field{height}) is similar to the
>> +native panel resolution in EDID display information, except that in
>> +the virtual machine case the size can change when the host window
>> +representing the guest display is gets resized.
>> +
>> +The position (fields \field{x} and \field{y}) describe how the
>> +displays are arranged (i.e. which is -- for example -- the left
>> +display).
>> +
>> +The \field{enabled} field is set when the user enabled the display.
>> +It is roughly the same as the connected state of a phyiscal display
>> +connector.
>> +
>> +\item[VIRTIO_GPU_CMD_RESOURCE_CREATE_2D] Create a 2D resource on the
>> + host. Request data is \field{struct virtio_gpu_resource_create_2d}.
>> + Response type is VIRTIO_GPU_RESP_OK_NODATA.
>> +
>> +\begin{lstlisting}
>> +enum virtio_gpu_formats {
>> + VIRTIO_GPU_FORMAT_B8G8R8A8_UNORM = 1,
>> + VIRTIO_GPU_FORMAT_B8G8R8X8_UNORM = 2,
>> + VIRTIO_GPU_FORMAT_A8R8G8B8_UNORM = 3,
>> + VIRTIO_GPU_FORMAT_X8R8G8B8_UNORM = 4,
>> +
>> + VIRTIO_GPU_FORMAT_R8G8B8A8_UNORM = 67,
>> + VIRTIO_GPU_FORMAT_X8B8G8R8_UNORM = 68,
>> +
>> + VIRTIO_GPU_FORMAT_A8B8G8R8_UNORM = 121,
>> + VIRTIO_GPU_FORMAT_R8G8B8X8_UNORM = 134,
>> +};
>> +
>> +struct virtio_gpu_resource_create_2d {
>> + struct virtio_gpu_ctrl_hdr hdr;
>> + le32 resource_id;
>> + le32 format;
>> + le32 width;
>> + le32 height;
>> +};
>> +\end{lstlisting}
>> +
>> +This creates a 2D resource on the host with the specified width,
>> +height and format. The resource ids are generated by the guest.
>> +
>> +\item[VIRTIO_GPU_CMD_RESOURCE_UNREF] Destroy a resource. Request data
>> + is \field{struct virtio_gpu_resource_unref}. Response type is
>> + VIRTIO_GPU_RESP_OK_NODATA.
>> +
>> +\begin{lstlisting}
>> +struct virtio_gpu_resource_unref {
>> + struct virtio_gpu_ctrl_hdr hdr;
>> + le32 resource_id;
>> + le32 padding;
>> +};
>> +\end{lstlisting}
>> +
>> +This informs the host that a resource is no longer required by the
>> +guest.
>> +
>> +\item[VIRTIO_GPU_CMD_SET_SCANOUT] Set the scanout parameters for a
>> + single output. Request data is \field{struct
>> + virtio_gpu_set_scanout}. Response type is
>> + VIRTIO_GPU_RESP_OK_NODATA.
>> +
>> +\begin{lstlisting}
>> +struct virtio_gpu_set_scanout {
>> + struct virtio_gpu_ctrl_hdr hdr;
>> + struct virtio_gpu_rect r;
>> + le32 scanout_id;
>> + le32 resource_id;
>> +};
>> +\end{lstlisting}
>> +
>> +This sets the scanout parameters for a single scanout. The resource_id
>> +is the resource to be scanned out from, along with a rectangle.
>> +
>> +Scanout rectangles must be completely covered by the underlying
>> +resource. Overlapping (or identical) scanouts are allowed, typical
>> +use case is screen mirroring.
>> +
>> +The driver can use resource_id = 0 to disable a scanout.
>> +
>> +\item[VIRTIO_GPU_CMD_RESOURCE_FLUSH] Flush a scanout resource Request
>> + data is \field{struct virtio_gpu_resource_flush}. Response type is
>> + VIRTIO_GPU_RESP_OK_NODATA.
>> +
>> +\begin{lstlisting}
>> +struct virtio_gpu_resource_flush {
>> + struct virtio_gpu_ctrl_hdr hdr;
>> + struct virtio_gpu_rect r;
>> + le32 resource_id;
>> + le32 padding;
>> +};
>> +\end{lstlisting}
>> +
>> +This flushes a resource to screen. It takes a rectangle and a
>> +resource id, and flushes any scanouts the resource is being used on.
>> +
>> +\item[VIRTIO_GPU_CMD_TRANSFER_TO_HOST_2D] Transfer from guest memory
>> + to host resource. Request data is \field{struct
>> + virtio_gpu_transfer_to_host_2d}. Response type is
>> + VIRTIO_GPU_RESP_OK_NODATA.
>> +
>> +\begin{lstlisting}
>> +struct virtio_gpu_transfer_to_host_2d {
>> + struct virtio_gpu_ctrl_hdr hdr;
>> + struct virtio_gpu_rect r;
>> + le64 offset;
>> + le32 resource_id;
>> + le32 padding;
>> +};
>> +\end{lstlisting}
>> +
>> +This takes a resource id along with an destination offset into the
>> +resource, and a box to transfer to the host backing for the resource.
>> +
>> +\item[VIRTIO_GPU_CMD_RESOURCE_ATTACH_BACKING] Assign backing pages to
>> + a resource. Request data is \field{struct
>> + virtio_gpu_resource_attach_backing}, followed by \field{struct
>> + virtio_gpu_mem_entry} entries. Response type is
>> + VIRTIO_GPU_RESP_OK_NODATA.
>> +
>> +\begin{lstlisting}
>> +struct virtio_gpu_resource_attach_backing {
>> + struct virtio_gpu_ctrl_hdr hdr;
>> + le32 resource_id;
>> + le32 nr_entries;
>> +};
>> +
>> +struct virtio_gpu_mem_entry {
>> + le64 addr;
>> + le32 length;
>> + le32 padding;
>> +};
>> +\end{lstlisting}
>> +
>> +This assign an array of guest pages as the backing store for a
>> +resource. These pages are then used for the transfer operations for
>> +that resource from that point on.
>> +
>> +\item[VIRTIO_GPU_CMD_RESOURCE_DETACH_BACKING] Detach backing pages
>> + from a resource. Request data is \field{struct
>> + virtio_gpu_resource_detach_backing}. Response type is
>> + VIRTIO_GPU_RESP_OK_NODATA.
>> +
>> +\begin{lstlisting}
>> +struct virtio_gpu_resource_detach_backing {
>> + struct virtio_gpu_ctrl_hdr hdr;
>> + le32 resource_id;
>> + le32 padding;
>> +};
>> +\end{lstlisting}
>> +
>> +This detaches any backing pages from a resource, to be used in case of
>> +guest swapping or object destruction.
>> +
>> +\end{description}
>> +
>> +\subsubsection{Device Operation: cursorq}\label{sec:Device Types / GPU Device / Device Operation / Device Operation: cursorq}
>> +
>> +Both cursorq commands use the same command struct.
>> +
>> +\begin{lstlisting}
>> +struct virtio_gpu_cursor_pos {
>> + le32 scanout_id;
>> + le32 x;
>> + le32 y;
>> + le32 padding;
>> +};
>> +
>> +struct virtio_gpu_update_cursor {
>> + struct virtio_gpu_ctrl_hdr hdr;
>> + struct virtio_gpu_cursor_pos pos;
>> + le32 resource_id;
>> + le32 hot_x;
>> + le32 hot_y;
>> + le32 padding;
>> +};
>> +\end{lstlisting}
>> +
>> +\begin{description}
>> +
>> +\item[VIRTIO_GPU_CMD_UPDATE_CURSOR]
>> +Update cursor.
>> +Request data is \field{struct virtio_gpu_update_cursor}.
>> +Response type is VIRTIO_GPU_RESP_OK_NODATA.
>> +
>> +Full cursor update. Cursor will be loaded from the specified
>> +\field{resource_id} and will be moved to \field{pos}. The driver must
>> +transfer the cursor into the resource beforehand (using control queue
>> +commands) and make sure the commands to fill the resource are actually
>> +processed (using fencing).
>> +
>> +\item[VIRTIO_GPU_CMD_MOVE_CURSOR]
>> +Move cursor.
>> +Request data is \field{struct virtio_gpu_update_cursor}.
>> +Response type is VIRTIO_GPU_RESP_OK_NODATA.
>> +
>> +Move cursor to the place specified in \field{pos}. The other fields
>> +are not used and will be ignored by the device.
>> +
>> +\end{description}
>> +
>> +\subsection{VGA Compatibility}\label{sec:Device Types / GPU Device / VGA Compatibility}
>> +
>> +Applies to Virtio Over PCI only. The GPU device can come with and
>> +without VGA compatibility. The PCI class should be DISPLAY_VGA if VGA
>> +compatibility is present and DISPLAY_OTHER otherwise.
>> +
>> +VGA compatibility: PCI region 0 has the linear framebuffer, standard
>> +vga registers are present. Configuring a scanout
>> +(VIRTIO_GPU_CMD_SET_SCANOUT) switches the device from vga
>> +compatibility mode into native virtio mode. A reset switches it back
>> +into vga compatibility mode.
>> +
>> +Note: qemu implementation also provides bochs dispi interface io ports
>> +and mmio bar at pci region 1 and is therefore fully compatible with
>> +the qemu stdvga (see \href{http://git.qemu-project.org/?p=qemu.git;a=blob;f=docs/specs/standard-vga.txt;hb=HEAD}{docs/specs/standard-vga.txt} in the qemu source tree).
>> --
>> 2.9.3
>>
>>
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