Adding upstream version 4.19.249.upstream/4.19.249upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 590 insertions, 0 deletions

diff --git a/Documentation/gpu/drm-kms.rst b/Documentation/gpu/drm-kms.rst
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+=========================
+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:
+
+.. kernel-doc:: drivers/gpu/drm/drm_atomic.c
+   :internal:
+
+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/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:
+
+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.c
+   :doc: explicit fencing 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: