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linux-dmabuf: mark as stable

Browse source 
This protocol extension is ubiquitous. It's time to mark it as
stable.

The interface names are left unchanged, so that compositors and
clients don't need to be updated. In particular, the legacy "z"
prefix is still part of the interface name.

Signed-off-by: Simon Ser <contact@emersion.fr>
This commit is contained in:
Simon Ser 2023-07-03 10:14:38 +02:00
parent a113a93d83
commit 51bee6e074
6 changed files with 813 additions and 8 deletions
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1
meson.build
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@ -12,6 +12,7 @@ stable_protocols = {
'presentation-time': [''],
'viewporter': [''],
'xdg-shell': [''],
'linux-dmabuf': ['v1'],
}
unstable_protocols = {

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stable/linux-dmabuf/README Normal file
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Linux DMA-BUF protocol
Maintainers:
Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Daniel Stone <daniels@collabora.com>

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.. Copyright 2021 Simon Ser
.. contents::
linux-dmabuf feedback introduction
==================================
linux-dmabuf feedback allows compositors and clients to negotiate optimal buffer
allocation parameters. This document will assume that the compositor is using a
rendering API such as OpenGL or Vulkan and KMS as the presentation API: even if
linux-dmabuf feedback isn't restricted to this use-case, it's the most common.
linux-dmabuf feedback introduces the following concepts:
1. A main device. This is the render device that the compositor is using to
perform composition. Compositors should always be able to display a buffer
submitted by a client, so this device can be used as a fallback in case none
of the more optimized code-paths work. Clients should allocate buffers such
that they can be imported and textured from the main device.
2. One or more tranches. Each tranche consists of a target device, allocation
flags and a set of format/modifier pairs. A tranche can be seen as a set of
formats/modifier pairs that are compatible with the target device.
A tranche can have the ``scanout`` flag. It means that the target device is
a KMS device, and that buffers allocated with one of the format/modifier
pairs in the tranche are eligible for direct scanout.
Clients should use the tranches in order to allocate buffers with the most
appropriate format/modifier and also to avoid allocating in private device
memory when cross-device operations are going to happen.
linux-dmabuf feedback implementation notes
==========================================
This section contains recommendations for client and compositor implementations.
For clients
-----------
Clients are expected to either pick a fixed DRM format beforehand, or
perform the following steps repeatedly until they find a suitable format.
Basic clients may only support static buffer allocation on startup. These
clients should do the following:
1. Send a ``get_default_feedback`` request to get global feedback.
2. Select the device indicated by ``main_device`` for allocation.
3. For each tranche:
1. If ``tranche_target_device`` doesn't match the allocation device, ignore
the tranche.
2. Accumulate allocation flags from ``tranche_flags``.
3. Accumulate format/modifier pairs received via ``tranche_formats`` in a
list.
4. When the ``tranche_done`` event is received, try to allocate the buffer
with the accumulated list of modifiers and allocation flags. If that
fails, proceed with the next tranche. If that succeeds, stop the loop.
4. Destroy the feedback object.
Tranches are ordered by preference: the more optimized tranches come first. As
such, clients should use the first tranche that happens to work.
Some clients may have already selected the device they want to use beforehand.
These clients can ignore the ``main_device`` event, and ignore tranches whose
``tranche_target_device`` doesn't match the selected device. Such clients need
to be prepared for the ``wp_linux_buffer_params.create`` request to potentially
fail.
If the client allocates a buffer without specifying explicit modifiers on a
device different from the one indicated by ``main_device``, then the client
must force a linear layout.
Some clients might support re-negotiating the buffer format/modifier on the
fly. These clients should send a ``get_surface_feedback`` request and keep the
feedback object alive after the initial allocation. Each time a new set of
feedback parameters is received (ended by the ``done`` event), they should
perform the same steps as basic clients described above. They should detect
when the optimal allocation parameters didn't change (same
format/modifier/flags) to avoid needlessly re-allocating their buffers.
Some clients might additionally support switching the device used for
allocations on the fly. Such clients should send a ``get_surface_feedback``
request. For each tranche, select the device indicated by
``tranche_target_device`` for allocation. Accumulate allocation flags (received
via ``tranche_flags``) and format/modifier pairs (received via
``tranche_formats``) as usual. When the ``tranche_done`` event is received, try
to allocate the buffer with the accumulated list of modifiers and the
allocation flags. Try to import the resulting buffer by sending a
``wp_linux_buffer_params.create`` request (this might fail). Repeat with each
tranche until an allocation and import succeeds. Each time a new set of
feedback parameters is received, they should perform these steps again. They
should detect when the optimal allocation parameters didn't change (same
device/format/modifier/flags) to avoid needlessly re-allocating their buffers.
For compositors
---------------
Basic compositors may only support texturing the DMA-BUFs via a rendering API
such as OpenGL or Vulkan. Such compositors can send a single tranche as a reply
to both ``get_default_feedback`` and ``get_surface_feedback``. Set the
``main_device`` to the rendering device. Send the tranche with
``tranche_target_device`` set to the rendering device and all of the DRM
format/modifier pairs supported by the rendering API. Do not set the
``scanout`` flag in the ``tranche_flags`` event.
Some compositors may support direct scan-out for full-screen surfaces. These
compositors can re-send the feedback parameters when a surface becomes
full-screen or leaves full-screen mode if the client has used the
``get_surface_feedback`` request. The non-full-screen feedback parameters are
the same as basic compositors described above. The full-screen feedback
parameters have two tranches: one with the format/modifier pairs supported by
the KMS plane, with the ``scanout`` flag set in the ``tranche_flags`` event and
with ``tranche_target_device`` set to the KMS scan-out device; the other with
the rest of the format/modifier pairs (supported for texturing, but not for
scan-out), without the ``scanout`` flag set in the ``tranche_flags`` event, and
with the ``tranche_target_device`` set to the rendering device.
Some compositors may support direct scan-out for all surfaces. These
compositors can send two tranches for surfaces that become candidates for
direct scan-out, similarly to compositors supporting direct scan-out for
fullscreen surfaces. When a surface stops being a candidate for direct
scan-out, compositors should re-send the feedback parameters optimized for
texturing only. The way candidates for direct scan-out are selected is
compositor policy, a possible implementation is to select as many surfaces as
there are available hardware planes, starting from surfaces closer to the eye.
Some compositors may support multiple devices at the same time. If the
compositor supports rendering with a fixed device and direct scan-out on a
secondary device, it may send a separate tranche for surfaces displayed on
the secondary device that are candidates for direct scan-out. The
``tranche_target_device`` for this tranche will be the secondary device and
will not match the ``main_device``.
Some compositors may support switching their rendering device at runtime or
changing their rendering device depending on the surface. When the rendering
device changes for a surface, such compositors may re-send the feedback
parameters with a different ``main_device``. However there is a risk that
clients don't support switching their device at runtime and continue using the
previous device. For this reason, compositors should always have a fallback
rendering device that they initially send as ``main_device``, such that these
clients use said fallback device.
Compositors should not change the ``main_device`` on-the-fly when explicit
modifiers are not supported, because there's a risk of importing buffers
with an implicit non-linear modifier as a linear buffer, resulting in
misinterpreted buffer contents.
Compositors should not send feedback parameters if they don't have a fallback
path. For instance, compositors shouldn't send a format/modifier supported for
direct scan-out but not supported by the rendering API for texturing.
Compositors can decide to use multiple tranches to describe the allocation
parameters optimized for texturing. For example, if there are formats which
have a fast texturing path and formats which have a slower texturing path, the
compositor can decide to expose two separate tranches.
Compositors can decide to use intermediate tranches to describe code-paths
slower than direct scan-out but faster than texturing. For instance, a
compositor could insert an intermediate tranche if it's possible to use a
mem2mem device to convert buffers to be able to use scan-out.
``dev_t`` encoding
==================
The protocol carries ``dev_t`` values on the wire using arrays. A compositor
written in C can encode the values as follows:
.. code-block:: c
struct stat drm_node_stat;
struct wl_array dev_array = {
.size = sizeof(drm_node_stat.st_rdev),
.data = &drm_node_stat.st_rdev,
};
A client can decode the values as follows:
.. code-block:: c
dev_t dev;
assert(dev_array->size == sizeof(dev));
memcpy(&dev, dev_array->data, sizeof(dev));
Because two DRM nodes can refer to the same DRM device while having different
``dev_t`` values, clients should use ``drmDevicesEqual`` to compare two
devices.
``format_table`` encoding
=========================
The ``format_table`` event carries a file descriptor containing a list of
format + modifier pairs. The list is an array of pairs which can be accessed
with this C structure definition:
.. code-block:: c
struct dmabuf_format_modifier {
uint32_t format;
uint32_t pad; /* unused */
uint64_t modifier;
};
Integration with other APIs
===========================
- libdrm: ``drmGetDeviceFromDevId`` returns a ``drmDevice`` from a device ID.
- EGL: the `EGL_EXT_device_drm_render_node`_ extension may be used to query the
DRM device render node used by a given EGL display. When unavailable, the
older `EGL_EXT_device_drm`_ extension may be used as a fallback.
- Vulkan: the `VK_EXT_physical_device_drm`_ extension may be used to query the
DRM device used by a given ``VkPhysicalDevice``.
.. _EGL_EXT_device_drm: https://www.khronos.org/registry/EGL/extensions/EXT/EGL_EXT_device_drm.txt
.. _EGL_EXT_device_drm_render_node: https://www.khronos.org/registry/EGL/extensions/EXT/EGL_EXT_device_drm_render_node.txt
.. _VK_EXT_physical_device_drm: https://www.khronos.org/registry/vulkan/specs/1.2-extensions/man/html/VK_EXT_physical_device_drm.html

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<?xml version="1.0" encoding="UTF-8"?>
<protocol name="linux_dmabuf_v1">
<copyright>
Copyright © 2014, 2015 Collabora, Ltd.
Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and associated documentation files (the "Software"),
to deal in the Software without restriction, including without limitation
the rights to use, copy, modify, merge, publish, distribute, sublicense,
and/or sell copies of the Software, and to permit persons to whom the
Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice (including the next
paragraph) shall be included in all copies or substantial portions of the
Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
DEALINGS IN THE SOFTWARE.
</copyright>
<interface name="zwp_linux_dmabuf_v1" version="4">
<description summary="factory for creating dmabuf-based wl_buffers">
Following the interfaces from:
https://www.khronos.org/registry/egl/extensions/EXT/EGL_EXT_image_dma_buf_import.txt
https://www.khronos.org/registry/EGL/extensions/EXT/EGL_EXT_image_dma_buf_import_modifiers.txt
and the Linux DRM sub-system's AddFb2 ioctl.
This interface offers ways to create generic dmabuf-based wl_buffers.
Clients can use the get_surface_feedback request to get dmabuf feedback
for a particular surface. If the client wants to retrieve feedback not
tied to a surface, they can use the get_default_feedback request.
The following are required from clients:
- Clients must ensure that either all data in the dma-buf is
coherent for all subsequent read access or that coherency is
correctly handled by the underlying kernel-side dma-buf
implementation.
- Don't make any more attachments after sending the buffer to the
compositor. Making more attachments later increases the risk of
the compositor not being able to use (re-import) an existing
dmabuf-based wl_buffer.
The underlying graphics stack must ensure the following:
- The dmabuf file descriptors relayed to the server will stay valid
for the whole lifetime of the wl_buffer. This means the server may
at any time use those fds to import the dmabuf into any kernel
sub-system that might accept it.
However, when the underlying graphics stack fails to deliver the
promise, because of e.g. a device hot-unplug which raises internal
errors, after the wl_buffer has been successfully created the
compositor must not raise protocol errors to the client when dmabuf
import later fails.
To create a wl_buffer from one or more dmabufs, a client creates a
zwp_linux_dmabuf_params_v1 object with a zwp_linux_dmabuf_v1.create_params
request. All planes required by the intended format are added with
the 'add' request. Finally, a 'create' or 'create_immed' request is
issued, which has the following outcome depending on the import success.
The 'create' request,
- on success, triggers a 'created' event which provides the final
wl_buffer to the client.
- on failure, triggers a 'failed' event to convey that the server
cannot use the dmabufs received from the client.
For the 'create_immed' request,
- on success, the server immediately imports the added dmabufs to
create a wl_buffer. No event is sent from the server in this case.
- on failure, the server can choose to either:
- terminate the client by raising a fatal error.
- mark the wl_buffer as failed, and send a 'failed' event to the
client. If the client uses a failed wl_buffer as an argument to any
request, the behaviour is compositor implementation-defined.
For all DRM formats and unless specified in another protocol extension,
pre-multiplied alpha is used for pixel values.
Unless specified otherwise in another protocol extension, implicit
synchronization is used. In other words, compositors and clients must
wait and signal fences implicitly passed via the DMA-BUF's reservation
mechanism.
</description>
<request name="destroy" type="destructor">
<description summary="unbind the factory">
Objects created through this interface, especially wl_buffers, will
remain valid.
</description>
</request>
<request name="create_params">
<description summary="create a temporary object for buffer parameters">
This temporary object is used to collect multiple dmabuf handles into
a single batch to create a wl_buffer. It can only be used once and
should be destroyed after a 'created' or 'failed' event has been
received.
</description>
<arg name="params_id" type="new_id" interface="zwp_linux_buffer_params_v1"
summary="the new temporary"/>
</request>
<event name="format">
<description summary="supported buffer format">
This event advertises one buffer format that the server supports.
All the supported formats are advertised once when the client
binds to this interface. A roundtrip after binding guarantees
that the client has received all supported formats.
For the definition of the format codes, see the
zwp_linux_buffer_params_v1::create request.
Starting version 4, the format event is deprecated and must not be
sent by compositors. Instead, use get_default_feedback or
get_surface_feedback.
</description>
<arg name="format" type="uint" summary="DRM_FORMAT code"/>
</event>
<event name="modifier" since="3">
<description summary="supported buffer format modifier">
This event advertises the formats that the server supports, along with
the modifiers supported for each format. All the supported modifiers
for all the supported formats are advertised once when the client
binds to this interface. A roundtrip after binding guarantees that
the client has received all supported format-modifier pairs.
For legacy support, DRM_FORMAT_MOD_INVALID (that is, modifier_hi ==
0x00ffffff and modifier_lo == 0xffffffff) is allowed in this event.
It indicates that the server can support the format with an implicit
modifier. When a plane has DRM_FORMAT_MOD_INVALID as its modifier, it
is as if no explicit modifier is specified. The effective modifier
will be derived from the dmabuf.
A compositor that sends valid modifiers and DRM_FORMAT_MOD_INVALID for
a given format supports both explicit modifiers and implicit modifiers.
For the definition of the format and modifier codes, see the
zwp_linux_buffer_params_v1::create and zwp_linux_buffer_params_v1::add
requests.
Starting version 4, the modifier event is deprecated and must not be
sent by compositors. Instead, use get_default_feedback or
get_surface_feedback.
</description>
<arg name="format" type="uint" summary="DRM_FORMAT code"/>
<arg name="modifier_hi" type="uint"
summary="high 32 bits of layout modifier"/>
<arg name="modifier_lo" type="uint"
summary="low 32 bits of layout modifier"/>
</event>
<!-- Version 4 additions -->
<request name="get_default_feedback" since="4">
<description summary="get default feedback">
This request creates a new wp_linux_dmabuf_feedback object not bound
to a particular surface. This object will deliver feedback about dmabuf
parameters to use if the client doesn't support per-surface feedback
(see get_surface_feedback).
</description>
<arg name="id" type="new_id" interface="zwp_linux_dmabuf_feedback_v1"/>
</request>
<request name="get_surface_feedback" since="4">
<description summary="get feedback for a surface">
This request creates a new wp_linux_dmabuf_feedback object for the
specified wl_surface. This object will deliver feedback about dmabuf
parameters to use for buffers attached to this surface.
If the surface is destroyed before the wp_linux_dmabuf_feedback object,
the feedback object becomes inert.
</description>
<arg name="id" type="new_id" interface="zwp_linux_dmabuf_feedback_v1"/>
<arg name="surface" type="object" interface="wl_surface"/>
</request>
</interface>
<interface name="zwp_linux_buffer_params_v1" version="4">
<description summary="parameters for creating a dmabuf-based wl_buffer">
This temporary object is a collection of dmabufs and other
parameters that together form a single logical buffer. The temporary
object may eventually create one wl_buffer unless cancelled by
destroying it before requesting 'create'.
Single-planar formats only require one dmabuf, however
multi-planar formats may require more than one dmabuf. For all
formats, an 'add' request must be called once per plane (even if the
underlying dmabuf fd is identical).
You must use consecutive plane indices ('plane_idx' argument for 'add')
from zero to the number of planes used by the drm_fourcc format code.
All planes required by the format must be given exactly once, but can
be given in any order. Each plane index can be set only once.
</description>
<enum name="error">
<entry name="already_used" value="0"
summary="the dmabuf_batch object has already been used to create a wl_buffer"/>
<entry name="plane_idx" value="1"
summary="plane index out of bounds"/>
<entry name="plane_set" value="2"
summary="the plane index was already set"/>
<entry name="incomplete" value="3"
summary="missing or too many planes to create a buffer"/>
<entry name="invalid_format" value="4"
summary="format not supported"/>
<entry name="invalid_dimensions" value="5"
summary="invalid width or height"/>
<entry name="out_of_bounds" value="6"
summary="offset + stride * height goes out of dmabuf bounds"/>
<entry name="invalid_wl_buffer" value="7"
summary="invalid wl_buffer resulted from importing dmabufs via
the create_immed request on given buffer_params"/>
</enum>
<request name="destroy" type="destructor">
<description summary="delete this object, used or not">
Cleans up the temporary data sent to the server for dmabuf-based
wl_buffer creation.
</description>
</request>
<request name="add">
<description summary="add a dmabuf to the temporary set">
This request adds one dmabuf to the set in this
zwp_linux_buffer_params_v1.
The 64-bit unsigned value combined from modifier_hi and modifier_lo
is the dmabuf layout modifier. DRM AddFB2 ioctl calls this the
fb modifier, which is defined in drm_mode.h of Linux UAPI.
This is an opaque token. Drivers use this token to express tiling,
compression, etc. driver-specific modifications to the base format
defined by the DRM fourcc code.
Starting from version 4, the invalid_format protocol error is sent if
the format + modifier pair was not advertised as supported.
This request raises the PLANE_IDX error if plane_idx is too large.
The error PLANE_SET is raised if attempting to set a plane that
was already set.
</description>
<arg name="fd" type="fd" summary="dmabuf fd"/>
<arg name="plane_idx" type="uint" summary="plane index"/>
<arg name="offset" type="uint" summary="offset in bytes"/>
<arg name="stride" type="uint" summary="stride in bytes"/>
<arg name="modifier_hi" type="uint"
summary="high 32 bits of layout modifier"/>
<arg name="modifier_lo" type="uint"
summary="low 32 bits of layout modifier"/>
</request>
<enum name="flags" bitfield="true">
<entry name="y_invert" value="1" summary="contents are y-inverted"/>
<entry name="interlaced" value="2" summary="content is interlaced"/>
<entry name="bottom_first" value="4" summary="bottom field first"/>
</enum>
<request name="create">
<description summary="create a wl_buffer from the given dmabufs">
This asks for creation of a wl_buffer from the added dmabuf
buffers. The wl_buffer is not created immediately but returned via
the 'created' event if the dmabuf sharing succeeds. The sharing
may fail at runtime for reasons a client cannot predict, in
which case the 'failed' event is triggered.
The 'format' argument is a DRM_FORMAT code, as defined by the
libdrm's drm_fourcc.h. The Linux kernel's DRM sub-system is the
authoritative source on how the format codes should work.
The 'flags' is a bitfield of the flags defined in enum "flags".
'y_invert' means the that the image needs to be y-flipped.
Flag 'interlaced' means that the frame in the buffer is not
progressive as usual, but interlaced. An interlaced buffer as
supported here must always contain both top and bottom fields.
The top field always begins on the first pixel row. The temporal
ordering between the two fields is top field first, unless
'bottom_first' is specified. It is undefined whether 'bottom_first'
is ignored if 'interlaced' is not set.
This protocol does not convey any information about field rate,
duration, or timing, other than the relative ordering between the
two fields in one buffer. A compositor may have to estimate the
intended field rate from the incoming buffer rate. It is undefined
whether the time of receiving wl_surface.commit with a new buffer
attached, applying the wl_surface state, wl_surface.frame callback
trigger, presentation, or any other point in the compositor cycle
is used to measure the frame or field times. There is no support
for detecting missed or late frames/fields/buffers either, and
there is no support whatsoever for cooperating with interlaced
compositor output.
The composited image quality resulting from the use of interlaced
buffers is explicitly undefined. A compositor may use elaborate
hardware features or software to deinterlace and create progressive
output frames from a sequence of interlaced input buffers, or it
may produce substandard image quality. However, compositors that
cannot guarantee reasonable image quality in all cases are recommended
to just reject all interlaced buffers.
Any argument errors, including non-positive width or height,
mismatch between the number of planes and the format, bad
format, bad offset or stride, may be indicated by fatal protocol
errors: INCOMPLETE, INVALID_FORMAT, INVALID_DIMENSIONS,
OUT_OF_BOUNDS.
Dmabuf import errors in the server that are not obvious client
bugs are returned via the 'failed' event as non-fatal. This
allows attempting dmabuf sharing and falling back in the client
if it fails.
This request can be sent only once in the object's lifetime, after
which the only legal request is destroy. This object should be
destroyed after issuing a 'create' request. Attempting to use this
object after issuing 'create' raises ALREADY_USED protocol error.
It is not mandatory to issue 'create'. If a client wants to
cancel the buffer creation, it can just destroy this object.
</description>
<arg name="width" type="int" summary="base plane width in pixels"/>
<arg name="height" type="int" summary="base plane height in pixels"/>
<arg name="format" type="uint" summary="DRM_FORMAT code"/>
<arg name="flags" type="uint" enum="flags" summary="see enum flags"/>
</request>
<event name="created">
<description summary="buffer creation succeeded">
This event indicates that the attempted buffer creation was
successful. It provides the new wl_buffer referencing the dmabuf(s).
Upon receiving this event, the client should destroy the
zwp_linux_buffer_params_v1 object.
</description>
<arg name="buffer" type="new_id" interface="wl_buffer"
summary="the newly created wl_buffer"/>
</event>
<event name="failed">
<description summary="buffer creation failed">
This event indicates that the attempted buffer creation has
failed. It usually means that one of the dmabuf constraints
has not been fulfilled.
Upon receiving this event, the client should destroy the
zwp_linux_buffer_params_v1 object.
</description>
</event>
<request name="create_immed" since="2">
<description summary="immediately create a wl_buffer from the given
dmabufs">
This asks for immediate creation of a wl_buffer by importing the
added dmabufs.
In case of import success, no event is sent from the server, and the
wl_buffer is ready to be used by the client.
Upon import failure, either of the following may happen, as seen fit
by the implementation:
- the client is terminated with one of the following fatal protocol
errors:
- INCOMPLETE, INVALID_FORMAT, INVALID_DIMENSIONS, OUT_OF_BOUNDS,
in case of argument errors such as mismatch between the number
of planes and the format, bad format, non-positive width or
height, or bad offset or stride.
- INVALID_WL_BUFFER, in case the cause for failure is unknown or
plaform specific.
- the server creates an invalid wl_buffer, marks it as failed and
sends a 'failed' event to the client. The result of using this
invalid wl_buffer as an argument in any request by the client is
defined by the compositor implementation.
This takes the same arguments as a 'create' request, and obeys the
same restrictions.
</description>
<arg name="buffer_id" type="new_id" interface="wl_buffer"
summary="id for the newly created wl_buffer"/>
<arg name="width" type="int" summary="base plane width in pixels"/>
<arg name="height" type="int" summary="base plane height in pixels"/>
<arg name="format" type="uint" summary="DRM_FORMAT code"/>
<arg name="flags" type="uint" enum="flags" summary="see enum flags"/>
</request>
</interface>
<interface name="zwp_linux_dmabuf_feedback_v1" version="4">
<description summary="dmabuf feedback">
This object advertises dmabuf parameters feedback. This includes the
preferred devices and the supported formats/modifiers.
The parameters are sent once when this object is created and whenever they
change. The done event is always sent once after all parameters have been
sent. When a single parameter changes, all parameters are re-sent by the
compositor.
Compositors can re-send the parameters when the current client buffer
allocations are sub-optimal. Compositors should not re-send the
parameters if re-allocating the buffers would not result in a more optimal
configuration. In particular, compositors should avoid sending the exact
same parameters multiple times in a row.
The tranche_target_device and tranche_formats events are grouped by
tranches of preference. For each tranche, a tranche_target_device, one
tranche_flags and one or more tranche_formats events are sent, followed
by a tranche_done event finishing the list. The tranches are sent in
descending order of preference. All formats and modifiers in the same
tranche have the same preference.
To send parameters, the compositor sends one main_device event, tranches
(each consisting of one tranche_target_device event, one tranche_flags
event, tranche_formats events and then a tranche_done event), then one
done event.
</description>
<request name="destroy" type="destructor">
<description summary="destroy the feedback object">
Using this request a client can tell the server that it is not going to
use the wp_linux_dmabuf_feedback object anymore.
</description>
</request>
<event name="done">
<description summary="all feedback has been sent">
This event is sent after all parameters of a wp_linux_dmabuf_feedback
object have been sent.
This allows changes to the wp_linux_dmabuf_feedback parameters to be
seen as atomic, even if they happen via multiple events.
</description>
</event>
<event name="format_table">
<description summary="format and modifier table">
This event provides a file descriptor which can be memory-mapped to
access the format and modifier table.
The table contains a tightly packed array of consecutive format +
modifier pairs. Each pair is 16 bytes wide. It contains a format as a
32-bit unsigned integer, followed by 4 bytes of unused padding, and a
modifier as a 64-bit unsigned integer. The native endianness is used.
The client must map the file descriptor in read-only private mode.
Compositors are not allowed to mutate the table file contents once this
event has been sent. Instead, compositors must create a new, separate
table file and re-send feedback parameters. Compositors are allowed to
store duplicate format + modifier pairs in the table.
</description>
<arg name="fd" type="fd" summary="table file descriptor"/>
<arg name="size" type="uint" summary="table size, in bytes"/>
</event>
<event name="main_device">
<description summary="preferred main device">
This event advertises the main device that the server prefers to use
when direct scan-out to the target device isn't possible. The
advertised main device may be different for each
wp_linux_dmabuf_feedback object, and may change over time.
There is exactly one main device. The compositor must send at least
one preference tranche with tranche_target_device equal to main_device.
Clients need to create buffers that the main device can import and
read from, otherwise creating the dmabuf wl_buffer will fail (see the
wp_linux_buffer_params.create and create_immed requests for details).
The main device will also likely be kept active by the compositor,
so clients can use it instead of waking up another device for power
savings.
In general the device is a DRM node. The DRM node type (primary vs.
render) is unspecified. Clients must not rely on the compositor sending
a particular node type. Clients cannot check two devices for equality
by comparing the dev_t value.
If explicit modifiers are not supported and the client performs buffer
allocations on a different device than the main device, then the client
must force the buffer to have a linear layout.
</description>
<arg name="device" type="array" summary="device dev_t value"/>
</event>
<event name="tranche_done">
<description summary="a preference tranche has been sent">
This event splits tranche_target_device and tranche_formats events in
preference tranches. It is sent after a set of tranche_target_device
and tranche_formats events; it represents the end of a tranche. The
next tranche will have a lower preference.
</description>
</event>
<event name="tranche_target_device">
<description summary="target device">
This event advertises the target device that the server prefers to use
for a buffer created given this tranche. The advertised target device
may be different for each preference tranche, and may change over time.
There is exactly one target device per tranche.
The target device may be a scan-out device, for example if the
compositor prefers to directly scan-out a buffer created given this
tranche. The target device may be a rendering device, for example if
the compositor prefers to texture from said buffer.
The client can use this hint to allocate the buffer in a way that makes
it accessible from the target device, ideally directly. The buffer must
still be accessible from the main device, either through direct import
or through a potentially more expensive fallback path. If the buffer
can't be directly imported from the main device then clients must be
prepared for the compositor changing the tranche priority or making
wl_buffer creation fail (see the wp_linux_buffer_params.create and
create_immed requests for details).
If the device is a DRM node, the DRM node type (primary vs. render) is
unspecified. Clients must not rely on the compositor sending a
particular node type. Clients cannot check two devices for equality by
comparing the dev_t value.
This event is tied to a preference tranche, see the tranche_done event.
</description>
<arg name="device" type="array" summary="device dev_t value"/>
</event>
<event name="tranche_formats">
<description summary="supported buffer format modifier">
This event advertises the format + modifier combinations that the
compositor supports.
It carries an array of indices, each referring to a format + modifier
pair in the last received format table (see the format_table event).
Each index is a 16-bit unsigned integer in native endianness.
For legacy support, DRM_FORMAT_MOD_INVALID is an allowed modifier.
It indicates that the server can support the format with an implicit
modifier. When a buffer has DRM_FORMAT_MOD_INVALID as its modifier, it
is as if no explicit modifier is specified. The effective modifier
will be derived from the dmabuf.
A compositor that sends valid modifiers and DRM_FORMAT_MOD_INVALID for
a given format supports both explicit modifiers and implicit modifiers.
Compositors must not send duplicate format + modifier pairs within the
same tranche or across two different tranches with the same target
device and flags.
This event is tied to a preference tranche, see the tranche_done event.
For the definition of the format and modifier codes, see the
wp_linux_buffer_params.create request.
</description>
<arg name="indices" type="array" summary="array of 16-bit indexes"/>
</event>
<enum name="tranche_flags" bitfield="true">
<entry name="scanout" value="1" summary="direct scan-out tranche"/>
</enum>
<event name="tranche_flags">
<description summary="tranche flags">
This event sets tranche-specific flags.
The scanout flag is a hint that direct scan-out may be attempted by the
compositor on the target device if the client appropriately allocates a
buffer. How to allocate a buffer that can be scanned out on the target
device is implementation-defined.
This event is tied to a preference tranche, see the tranche_done event.
</description>
<arg name="flags" type="uint" enum="tranche_flags" summary="tranche flags"/>
</event>
</interface>
</protocol>

4
unstable/linux-dmabuf/README
View file

@ -3,3 +3,7 @@ Linux DMA-BUF protocol
Maintainers:
Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Daniel Stone <daniels@collabora.com>
Disclaimer: This protocol extension has been marked stable. This copy is
no longer used and only retained for backwards compatibility. The
canonical version can be found in the stable/ directory.

11
unstable/linux-dmabuf/linux-dmabuf-unstable-v1.xml
View file

@ -91,14 +91,9 @@
wait and signal fences implicitly passed via the DMA-BUF's reservation
mechanism.
Warning! The protocol described in this file is experimental and
backward incompatible changes may be made. Backward compatible changes
may be added together with the corresponding interface version bump.
Backward incompatible changes are done by bumping the version number in
the protocol and interface names and resetting the interface version.
Once the protocol is to be declared stable, the 'z' prefix and the
version number in the protocol and interface names are removed and the
interface version number is reset.
Disclaimer: This protocol extension has been marked stable. This copy is
no longer used and only retained for backwards compatibility. The
canonical version can be found in the stable/ directory.
</description>
<request name="destroy" type="destructor">