622 lines
19 KiB
ReStructuredText
622 lines
19 KiB
ReStructuredText
=========================
|
|
Kernel Mode Setting (KMS)
|
|
=========================
|
|
|
|
Drivers must initialize the mode setting core by calling
|
|
:c:func:`drm_mode_config_init()` on the DRM device. The function
|
|
initializes the :c:type:`struct drm_device <drm_device>`
|
|
mode_config field and never fails. Once done, mode configuration must
|
|
be setup by initializing the following fields.
|
|
|
|
- int min_width, min_height; int max_width, max_height;
|
|
Minimum and maximum width and height of the frame buffers in pixel
|
|
units.
|
|
|
|
- struct drm_mode_config_funcs \*funcs;
|
|
Mode setting functions.
|
|
|
|
Overview
|
|
========
|
|
|
|
.. kernel-render:: DOT
|
|
:alt: KMS Display Pipeline
|
|
:caption: KMS Display Pipeline Overview
|
|
|
|
digraph "KMS" {
|
|
node [shape=box]
|
|
|
|
subgraph cluster_static {
|
|
style=dashed
|
|
label="Static Objects"
|
|
|
|
node [bgcolor=grey style=filled]
|
|
"drm_plane A" -> "drm_crtc"
|
|
"drm_plane B" -> "drm_crtc"
|
|
"drm_crtc" -> "drm_encoder A"
|
|
"drm_crtc" -> "drm_encoder B"
|
|
}
|
|
|
|
subgraph cluster_user_created {
|
|
style=dashed
|
|
label="Userspace-Created"
|
|
|
|
node [shape=oval]
|
|
"drm_framebuffer 1" -> "drm_plane A"
|
|
"drm_framebuffer 2" -> "drm_plane B"
|
|
}
|
|
|
|
subgraph cluster_connector {
|
|
style=dashed
|
|
label="Hotpluggable"
|
|
|
|
"drm_encoder A" -> "drm_connector A"
|
|
"drm_encoder B" -> "drm_connector B"
|
|
}
|
|
}
|
|
|
|
The basic object structure KMS presents to userspace is fairly simple.
|
|
Framebuffers (represented by :c:type:`struct drm_framebuffer <drm_framebuffer>`,
|
|
see `Frame Buffer Abstraction`_) feed into planes. Planes are represented by
|
|
:c:type:`struct drm_plane <drm_plane>`, see `Plane Abstraction`_ for more
|
|
details. One or more (or even no) planes feed their pixel data into a CRTC
|
|
(represented by :c:type:`struct drm_crtc <drm_crtc>`, see `CRTC Abstraction`_)
|
|
for blending. The precise blending step is explained in more detail in `Plane
|
|
Composition Properties`_ and related chapters.
|
|
|
|
For the output routing the first step is encoders (represented by
|
|
:c:type:`struct drm_encoder <drm_encoder>`, see `Encoder Abstraction`_). Those
|
|
are really just internal artifacts of the helper libraries used to implement KMS
|
|
drivers. Besides that they make it unecessarily more complicated for userspace
|
|
to figure out which connections between a CRTC and a connector are possible, and
|
|
what kind of cloning is supported, they serve no purpose in the userspace API.
|
|
Unfortunately encoders have been exposed to userspace, hence can't remove them
|
|
at this point. Futhermore the exposed restrictions are often wrongly set by
|
|
drivers, and in many cases not powerful enough to express the real restrictions.
|
|
A CRTC can be connected to multiple encoders, and for an active CRTC there must
|
|
be at least one encoder.
|
|
|
|
The final, and real, endpoint in the display chain is the connector (represented
|
|
by :c:type:`struct drm_connector <drm_connector>`, see `Connector
|
|
Abstraction`_). Connectors can have different possible encoders, but the kernel
|
|
driver selects which encoder to use for each connector. The use case is DVI,
|
|
which could switch between an analog and a digital encoder. Encoders can also
|
|
drive multiple different connectors. There is exactly one active connector for
|
|
every active encoder.
|
|
|
|
Internally the output pipeline is a bit more complex and matches today's
|
|
hardware more closely:
|
|
|
|
.. kernel-render:: DOT
|
|
:alt: KMS Output Pipeline
|
|
:caption: KMS Output Pipeline
|
|
|
|
digraph "Output Pipeline" {
|
|
node [shape=box]
|
|
|
|
subgraph {
|
|
"drm_crtc" [bgcolor=grey style=filled]
|
|
}
|
|
|
|
subgraph cluster_internal {
|
|
style=dashed
|
|
label="Internal Pipeline"
|
|
{
|
|
node [bgcolor=grey style=filled]
|
|
"drm_encoder A";
|
|
"drm_encoder B";
|
|
"drm_encoder C";
|
|
}
|
|
|
|
{
|
|
node [bgcolor=grey style=filled]
|
|
"drm_encoder B" -> "drm_bridge B"
|
|
"drm_encoder C" -> "drm_bridge C1"
|
|
"drm_bridge C1" -> "drm_bridge C2";
|
|
}
|
|
}
|
|
|
|
"drm_crtc" -> "drm_encoder A"
|
|
"drm_crtc" -> "drm_encoder B"
|
|
"drm_crtc" -> "drm_encoder C"
|
|
|
|
|
|
subgraph cluster_output {
|
|
style=dashed
|
|
label="Outputs"
|
|
|
|
"drm_encoder A" -> "drm_connector A";
|
|
"drm_bridge B" -> "drm_connector B";
|
|
"drm_bridge C2" -> "drm_connector C";
|
|
|
|
"drm_panel"
|
|
}
|
|
}
|
|
|
|
Internally two additional helper objects come into play. First, to be able to
|
|
share code for encoders (sometimes on the same SoC, sometimes off-chip) one or
|
|
more :ref:`drm_bridges` (represented by :c:type:`struct drm_bridge
|
|
<drm_bridge>`) can be linked to an encoder. This link is static and cannot be
|
|
changed, which means the cross-bar (if there is any) needs to be mapped between
|
|
the CRTC and any encoders. Often for drivers with bridges there's no code left
|
|
at the encoder level. Atomic drivers can leave out all the encoder callbacks to
|
|
essentially only leave a dummy routing object behind, which is needed for
|
|
backwards compatibility since encoders are exposed to userspace.
|
|
|
|
The second object is for panels, represented by :c:type:`struct drm_panel
|
|
<drm_panel>`, see :ref:`drm_panel_helper`. Panels do not have a fixed binding
|
|
point, but are generally linked to the driver private structure that embeds
|
|
:c:type:`struct drm_connector <drm_connector>`.
|
|
|
|
Note that currently the bridge chaining and interactions with connectors and
|
|
panels are still in-flux and not really fully sorted out yet.
|
|
|
|
KMS Core Structures and Functions
|
|
=================================
|
|
|
|
.. kernel-doc:: include/drm/drm_mode_config.h
|
|
:internal:
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_mode_config.c
|
|
:export:
|
|
|
|
Modeset Base Object Abstraction
|
|
===============================
|
|
|
|
.. kernel-render:: DOT
|
|
:alt: Mode Objects and Properties
|
|
:caption: Mode Objects and Properties
|
|
|
|
digraph {
|
|
node [shape=box]
|
|
|
|
"drm_property A" -> "drm_mode_object A"
|
|
"drm_property A" -> "drm_mode_object B"
|
|
"drm_property B" -> "drm_mode_object A"
|
|
}
|
|
|
|
The base structure for all KMS objects is :c:type:`struct drm_mode_object
|
|
<drm_mode_object>`. One of the base services it provides is tracking properties,
|
|
which are especially important for the atomic IOCTL (see `Atomic Mode
|
|
Setting`_). The somewhat surprising part here is that properties are not
|
|
directly instantiated on each object, but free-standing mode objects themselves,
|
|
represented by :c:type:`struct drm_property <drm_property>`, which only specify
|
|
the type and value range of a property. Any given property can be attached
|
|
multiple times to different objects using :c:func:`drm_object_attach_property()
|
|
<drm_object_attach_property>`.
|
|
|
|
.. kernel-doc:: include/drm/drm_mode_object.h
|
|
:internal:
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_mode_object.c
|
|
:export:
|
|
|
|
Atomic Mode Setting
|
|
===================
|
|
|
|
|
|
.. kernel-render:: DOT
|
|
:alt: Mode Objects and Properties
|
|
:caption: Mode Objects and Properties
|
|
|
|
digraph {
|
|
node [shape=box]
|
|
|
|
subgraph cluster_state {
|
|
style=dashed
|
|
label="Free-standing state"
|
|
|
|
"drm_atomic_state" -> "duplicated drm_plane_state A"
|
|
"drm_atomic_state" -> "duplicated drm_plane_state B"
|
|
"drm_atomic_state" -> "duplicated drm_crtc_state"
|
|
"drm_atomic_state" -> "duplicated drm_connector_state"
|
|
"drm_atomic_state" -> "duplicated driver private state"
|
|
}
|
|
|
|
subgraph cluster_current {
|
|
style=dashed
|
|
label="Current state"
|
|
|
|
"drm_device" -> "drm_plane A"
|
|
"drm_device" -> "drm_plane B"
|
|
"drm_device" -> "drm_crtc"
|
|
"drm_device" -> "drm_connector"
|
|
"drm_device" -> "driver private object"
|
|
|
|
"drm_plane A" -> "drm_plane_state A"
|
|
"drm_plane B" -> "drm_plane_state B"
|
|
"drm_crtc" -> "drm_crtc_state"
|
|
"drm_connector" -> "drm_connector_state"
|
|
"driver private object" -> "driver private state"
|
|
}
|
|
|
|
"drm_atomic_state" -> "drm_device" [label="atomic_commit"]
|
|
"duplicated drm_plane_state A" -> "drm_device"[style=invis]
|
|
}
|
|
|
|
Atomic provides transactional modeset (including planes) updates, but a
|
|
bit differently from the usual transactional approach of try-commit and
|
|
rollback:
|
|
|
|
- Firstly, no hardware changes are allowed when the commit would fail. This
|
|
allows us to implement the DRM_MODE_ATOMIC_TEST_ONLY mode, which allows
|
|
userspace to explore whether certain configurations would work or not.
|
|
|
|
- This would still allow setting and rollback of just the software state,
|
|
simplifying conversion of existing drivers. But auditing drivers for
|
|
correctness of the atomic_check code becomes really hard with that: Rolling
|
|
back changes in data structures all over the place is hard to get right.
|
|
|
|
- Lastly, for backwards compatibility and to support all use-cases, atomic
|
|
updates need to be incremental and be able to execute in parallel. Hardware
|
|
doesn't always allow it, but where possible plane updates on different CRTCs
|
|
should not interfere, and not get stalled due to output routing changing on
|
|
different CRTCs.
|
|
|
|
Taken all together there's two consequences for the atomic design:
|
|
|
|
- The overall state is split up into per-object state structures:
|
|
:c:type:`struct drm_plane_state <drm_plane_state>` for planes, :c:type:`struct
|
|
drm_crtc_state <drm_crtc_state>` for CRTCs and :c:type:`struct
|
|
drm_connector_state <drm_connector_state>` for connectors. These are the only
|
|
objects with userspace-visible and settable state. For internal state drivers
|
|
can subclass these structures through embeddeding, or add entirely new state
|
|
structures for their globally shared hardware functions.
|
|
|
|
- An atomic update is assembled and validated as an entirely free-standing pile
|
|
of structures within the :c:type:`drm_atomic_state <drm_atomic_state>`
|
|
container. Driver private state structures are also tracked in the same
|
|
structure; see the next chapter. Only when a state is committed is it applied
|
|
to the driver and modeset objects. This way rolling back an update boils down
|
|
to releasing memory and unreferencing objects like framebuffers.
|
|
|
|
Read on in this chapter, and also in :ref:`drm_atomic_helper` for more detailed
|
|
coverage of specific topics.
|
|
|
|
Handling Driver Private State
|
|
-----------------------------
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_atomic.c
|
|
:doc: handling driver private state
|
|
|
|
Atomic Mode Setting Function Reference
|
|
--------------------------------------
|
|
|
|
.. kernel-doc:: include/drm/drm_atomic.h
|
|
:internal:
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_atomic.c
|
|
:export:
|
|
|
|
Atomic Mode Setting IOCTL and UAPI Functions
|
|
--------------------------------------------
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_atomic_uapi.c
|
|
:doc: overview
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_atomic_uapi.c
|
|
:export:
|
|
|
|
CRTC Abstraction
|
|
================
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_crtc.c
|
|
:doc: overview
|
|
|
|
CRTC Functions Reference
|
|
--------------------------------
|
|
|
|
.. kernel-doc:: include/drm/drm_crtc.h
|
|
:internal:
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_crtc.c
|
|
:export:
|
|
|
|
Frame Buffer Abstraction
|
|
========================
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_framebuffer.c
|
|
:doc: overview
|
|
|
|
Frame Buffer Functions Reference
|
|
--------------------------------
|
|
|
|
.. kernel-doc:: include/drm/drm_framebuffer.h
|
|
:internal:
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_framebuffer.c
|
|
:export:
|
|
|
|
DRM Format Handling
|
|
===================
|
|
|
|
.. kernel-doc:: include/uapi/drm/drm_fourcc.h
|
|
:doc: overview
|
|
|
|
Format Functions Reference
|
|
--------------------------
|
|
|
|
.. kernel-doc:: include/drm/drm_fourcc.h
|
|
:internal:
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_fourcc.c
|
|
:export:
|
|
|
|
Dumb Buffer Objects
|
|
===================
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_dumb_buffers.c
|
|
:doc: overview
|
|
|
|
Plane Abstraction
|
|
=================
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_plane.c
|
|
:doc: overview
|
|
|
|
Plane Functions Reference
|
|
-------------------------
|
|
|
|
.. kernel-doc:: include/drm/drm_plane.h
|
|
:internal:
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_plane.c
|
|
:export:
|
|
|
|
Display Modes Function Reference
|
|
================================
|
|
|
|
.. kernel-doc:: include/drm/drm_modes.h
|
|
:internal:
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_modes.c
|
|
:export:
|
|
|
|
Connector Abstraction
|
|
=====================
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_connector.c
|
|
:doc: overview
|
|
|
|
Connector Functions Reference
|
|
-----------------------------
|
|
|
|
.. kernel-doc:: include/drm/drm_connector.h
|
|
:internal:
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_connector.c
|
|
:export:
|
|
|
|
Writeback Connectors
|
|
--------------------
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_writeback.c
|
|
:doc: overview
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_writeback.c
|
|
:export:
|
|
|
|
Encoder Abstraction
|
|
===================
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_encoder.c
|
|
:doc: overview
|
|
|
|
Encoder Functions Reference
|
|
---------------------------
|
|
|
|
.. kernel-doc:: include/drm/drm_encoder.h
|
|
:internal:
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_encoder.c
|
|
:export:
|
|
|
|
KMS Initialization and Cleanup
|
|
==============================
|
|
|
|
A KMS device is abstracted and exposed as a set of planes, CRTCs,
|
|
encoders and connectors. KMS drivers must thus create and initialize all
|
|
those objects at load time after initializing mode setting.
|
|
|
|
CRTCs (:c:type:`struct drm_crtc <drm_crtc>`)
|
|
--------------------------------------------
|
|
|
|
A CRTC is an abstraction representing a part of the chip that contains a
|
|
pointer to a scanout buffer. Therefore, the number of CRTCs available
|
|
determines how many independent scanout buffers can be active at any
|
|
given time. The CRTC structure contains several fields to support this:
|
|
a pointer to some video memory (abstracted as a frame buffer object), a
|
|
display mode, and an (x, y) offset into the video memory to support
|
|
panning or configurations where one piece of video memory spans multiple
|
|
CRTCs.
|
|
|
|
CRTC Initialization
|
|
~~~~~~~~~~~~~~~~~~~
|
|
|
|
A KMS device must create and register at least one struct
|
|
:c:type:`struct drm_crtc <drm_crtc>` instance. The instance is
|
|
allocated and zeroed by the driver, possibly as part of a larger
|
|
structure, and registered with a call to :c:func:`drm_crtc_init()`
|
|
with a pointer to CRTC functions.
|
|
|
|
|
|
Cleanup
|
|
-------
|
|
|
|
The DRM core manages its objects' lifetime. When an object is not needed
|
|
anymore the core calls its destroy function, which must clean up and
|
|
free every resource allocated for the object. Every
|
|
:c:func:`drm_\*_init()` call must be matched with a corresponding
|
|
:c:func:`drm_\*_cleanup()` call to cleanup CRTCs
|
|
(:c:func:`drm_crtc_cleanup()`), planes
|
|
(:c:func:`drm_plane_cleanup()`), encoders
|
|
(:c:func:`drm_encoder_cleanup()`) and connectors
|
|
(:c:func:`drm_connector_cleanup()`). Furthermore, connectors that
|
|
have been added to sysfs must be removed by a call to
|
|
:c:func:`drm_connector_unregister()` before calling
|
|
:c:func:`drm_connector_cleanup()`.
|
|
|
|
Connectors state change detection must be cleanup up with a call to
|
|
:c:func:`drm_kms_helper_poll_fini()`.
|
|
|
|
Output discovery and initialization example
|
|
-------------------------------------------
|
|
|
|
.. code-block:: c
|
|
|
|
void intel_crt_init(struct drm_device *dev)
|
|
{
|
|
struct drm_connector *connector;
|
|
struct intel_output *intel_output;
|
|
|
|
intel_output = kzalloc(sizeof(struct intel_output), GFP_KERNEL);
|
|
if (!intel_output)
|
|
return;
|
|
|
|
connector = &intel_output->base;
|
|
drm_connector_init(dev, &intel_output->base,
|
|
&intel_crt_connector_funcs, DRM_MODE_CONNECTOR_VGA);
|
|
|
|
drm_encoder_init(dev, &intel_output->enc, &intel_crt_enc_funcs,
|
|
DRM_MODE_ENCODER_DAC);
|
|
|
|
drm_connector_attach_encoder(&intel_output->base,
|
|
&intel_output->enc);
|
|
|
|
/* Set up the DDC bus. */
|
|
intel_output->ddc_bus = intel_i2c_create(dev, GPIOA, "CRTDDC_A");
|
|
if (!intel_output->ddc_bus) {
|
|
dev_printk(KERN_ERR, &dev->pdev->dev, "DDC bus registration "
|
|
"failed.\n");
|
|
return;
|
|
}
|
|
|
|
intel_output->type = INTEL_OUTPUT_ANALOG;
|
|
connector->interlace_allowed = 0;
|
|
connector->doublescan_allowed = 0;
|
|
|
|
drm_encoder_helper_add(&intel_output->enc, &intel_crt_helper_funcs);
|
|
drm_connector_helper_add(connector, &intel_crt_connector_helper_funcs);
|
|
|
|
drm_connector_register(connector);
|
|
}
|
|
|
|
In the example above (taken from the i915 driver), a CRTC, connector and
|
|
encoder combination is created. A device-specific i2c bus is also
|
|
created for fetching EDID data and performing monitor detection. Once
|
|
the process is complete, the new connector is registered with sysfs to
|
|
make its properties available to applications.
|
|
|
|
KMS Locking
|
|
===========
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_modeset_lock.c
|
|
:doc: kms locking
|
|
|
|
.. kernel-doc:: include/drm/drm_modeset_lock.h
|
|
:internal:
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_modeset_lock.c
|
|
:export:
|
|
|
|
KMS Properties
|
|
==============
|
|
|
|
Property Types and Blob Property Support
|
|
----------------------------------------
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_property.c
|
|
:doc: overview
|
|
|
|
.. kernel-doc:: include/drm/drm_property.h
|
|
:internal:
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_property.c
|
|
:export:
|
|
|
|
Standard Connector Properties
|
|
-----------------------------
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_connector.c
|
|
:doc: standard connector properties
|
|
|
|
HDMI Specific Connector Properties
|
|
----------------------------------
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_connector.c
|
|
:doc: HDMI connector properties
|
|
|
|
Plane Composition Properties
|
|
----------------------------
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_blend.c
|
|
:doc: overview
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_blend.c
|
|
:export:
|
|
|
|
FB_DAMAGE_CLIPS
|
|
~~~~~~~~~~~~~~~
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_damage_helper.c
|
|
:doc: overview
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_damage_helper.c
|
|
:export:
|
|
|
|
.. kernel-doc:: include/drm/drm_damage_helper.h
|
|
:internal:
|
|
|
|
Color Management Properties
|
|
---------------------------
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_color_mgmt.c
|
|
:doc: overview
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_color_mgmt.c
|
|
:export:
|
|
|
|
Tile Group Property
|
|
-------------------
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_connector.c
|
|
:doc: Tile group
|
|
|
|
Explicit Fencing Properties
|
|
---------------------------
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_atomic_uapi.c
|
|
:doc: explicit fencing properties
|
|
|
|
|
|
Variable Refresh Properties
|
|
---------------------------
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_connector.c
|
|
:doc: Variable refresh properties
|
|
|
|
Existing KMS Properties
|
|
-----------------------
|
|
|
|
The following table gives description of drm properties exposed by various
|
|
modules/drivers. Because this table is very unwieldy, do not add any new
|
|
properties here. Instead document them in a section above.
|
|
|
|
.. csv-table::
|
|
:header-rows: 1
|
|
:file: kms-properties.csv
|
|
|
|
Vertical Blanking
|
|
=================
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_vblank.c
|
|
:doc: vblank handling
|
|
|
|
Vertical Blanking and Interrupt Handling Functions Reference
|
|
------------------------------------------------------------
|
|
|
|
.. kernel-doc:: include/drm/drm_vblank.h
|
|
:internal:
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_vblank.c
|
|
:export:
|