diff options
Diffstat (limited to 'Documentation/gpu')
| -rw-r--r-- | Documentation/gpu/drm-internals.rst | 9 | ||||
| -rw-r--r-- | Documentation/gpu/drm-kms-helpers.rst | 221 | ||||
| -rw-r--r-- | Documentation/gpu/drm-kms.rst | 503 | ||||
| -rw-r--r-- | Documentation/gpu/drm-mm.rst | 58 | ||||
| -rw-r--r-- | Documentation/gpu/drm-uapi.rst | 107 | ||||
| -rw-r--r-- | Documentation/gpu/i915.rst | 3 | ||||
| -rw-r--r-- | Documentation/gpu/index.rst | 1 | ||||
| -rw-r--r-- | Documentation/gpu/kms-properties.csv | 21 | ||||
| -rw-r--r-- | Documentation/gpu/vgaarbiter.rst | 191 |
9 files changed, 575 insertions, 539 deletions
diff --git a/Documentation/gpu/drm-internals.rst b/Documentation/gpu/drm-internals.rst index 3bb26135971f..37284bcc7764 100644 --- a/Documentation/gpu/drm-internals.rst +++ b/Documentation/gpu/drm-internals.rst @@ -53,9 +53,12 @@ u32 driver_features; DRIVER_USE_AGP Driver uses AGP interface, the DRM core will manage AGP resources. -DRIVER_REQUIRE_AGP - Driver needs AGP interface to function. AGP initialization failure - will become a fatal error. +DRIVER_LEGACY + Denote a legacy driver using shadow attach. Don't use. + +DRIVER_KMS_LEGACY_CONTEXT + Used only by nouveau for backwards compatibility with existing userspace. + Don't use. DRIVER_PCI_DMA Driver is capable of PCI DMA, mapping of PCI DMA buffers to diff --git a/Documentation/gpu/drm-kms-helpers.rst b/Documentation/gpu/drm-kms-helpers.rst index 0b302fedf1af..bb4254d19cbb 100644 --- a/Documentation/gpu/drm-kms-helpers.rst +++ b/Documentation/gpu/drm-kms-helpers.rst @@ -2,38 +2,45 @@ Mode Setting Helper Functions ============================= -The plane, CRTC, encoder and connector functions provided by the drivers -implement the DRM API. They're called by the DRM core and ioctl handlers -to handle device state changes and configuration request. As -implementing those functions often requires logic not specific to -drivers, mid-layer helper functions are available to avoid duplicating -boilerplate code. - -The DRM core contains one mid-layer implementation. The mid-layer -provides implementations of several plane, CRTC, encoder and connector -functions (called from the top of the mid-layer) that pre-process -requests and call lower-level functions provided by the driver (at the -bottom of the mid-layer). For instance, the -:c:func:`drm_crtc_helper_set_config()` function can be used to -fill the :c:type:`struct drm_crtc_funcs <drm_crtc_funcs>` -set_config field. When called, it will split the set_config operation -in smaller, simpler operations and call the driver to handle them. - -To use the mid-layer, drivers call -:c:func:`drm_crtc_helper_add()`, -:c:func:`drm_encoder_helper_add()` and -:c:func:`drm_connector_helper_add()` functions to install their -mid-layer bottom operations handlers, and fill the :c:type:`struct -drm_crtc_funcs <drm_crtc_funcs>`, :c:type:`struct -drm_encoder_funcs <drm_encoder_funcs>` and :c:type:`struct -drm_connector_funcs <drm_connector_funcs>` structures with -pointers to the mid-layer top API functions. Installing the mid-layer -bottom operation handlers is best done right after registering the -corresponding KMS object. - -The mid-layer is not split between CRTC, encoder and connector -operations. To use it, a driver must provide bottom functions for all of -the three KMS entities. +The DRM subsystem aims for a strong separation between core code and helper +libraries. Core code takes care of general setup and teardown and decoding +userspace requests to kernel internal objects. Everything else is handled by a +large set of helper libraries, which can be combined freely to pick and choose +for each driver what fits, and avoid shared code where special behaviour is +needed. + +This distinction between core code and helpers is especially strong in the +modesetting code, where there's a shared userspace ABI for all drivers. This is +in contrast to the render side, where pretty much everything (with very few +exceptions) can be considered optional helper code. + +There are a few areas these helpers can grouped into: + +* Helpers to implement modesetting. The important ones here are the atomic + helpers. Old drivers still often use the legacy CRTC helpers. They both share + the same set of common helper vtables. For really simple drivers (anything + that would have been a great fit in the deprecated fbdev subsystem) there's + also the simple display pipe helpers. + +* There's a big pile of helpers for handling outputs. First the generic bridge + helpers for handling encoder and transcoder IP blocks. Second the panel helpers + for handling panel-related information and logic. Plus then a big set of + helpers for the various sink standards (DisplayPort, HDMI, MIPI DSI). Finally + there's also generic helpers for handling output probing, and for dealing with + EDIDs. + +* The last group of helpers concerns itself with the frontend side of a display + pipeline: Planes, handling rectangles for visibility checking and scissoring, + flip queues and assorted bits. + +Modeset Helper Reference for Common Vtables +=========================================== + +.. kernel-doc:: include/drm/drm_modeset_helper_vtables.h + :internal: + +.. kernel-doc:: include/drm/drm_modeset_helper_vtables.h + :doc: overview Atomic Modeset Helper Functions Reference ========================================= @@ -62,33 +69,27 @@ Atomic State Reset and Initialization .. kernel-doc:: drivers/gpu/drm/drm_atomic_helper.c :export: -Modeset Helper Reference for Common Vtables -=========================================== - -.. kernel-doc:: include/drm/drm_modeset_helper_vtables.h - :internal: - -.. kernel-doc:: include/drm/drm_modeset_helper_vtables.h - :doc: overview - Legacy CRTC/Modeset Helper Functions Reference ============================================== .. kernel-doc:: drivers/gpu/drm/drm_crtc_helper.c - :export: + :doc: overview .. kernel-doc:: drivers/gpu/drm/drm_crtc_helper.c - :doc: overview + :export: -Output Probing Helper Functions Reference -========================================= +Simple KMS Helper Reference +=========================== -.. kernel-doc:: drivers/gpu/drm/drm_probe_helper.c - :doc: output probing helper overview +.. kernel-doc:: include/drm/drm_simple_kms_helper.h + :internal: -.. kernel-doc:: drivers/gpu/drm/drm_probe_helper.c +.. kernel-doc:: drivers/gpu/drm/drm_simple_kms_helper.c :export: +.. kernel-doc:: drivers/gpu/drm/drm_simple_kms_helper.c + :doc: overview + fbdev Helper Functions Reference ================================ @@ -110,6 +111,43 @@ Framebuffer CMA Helper Functions Reference .. kernel-doc:: drivers/gpu/drm/drm_fb_cma_helper.c :export: +Bridges +======= + +Overview +-------- + +.. kernel-doc:: drivers/gpu/drm/drm_bridge.c + :doc: overview + +Default bridge callback sequence +-------------------------------- + +.. kernel-doc:: drivers/gpu/drm/drm_bridge.c + :doc: bridge callbacks + + +Bridge Helper Reference +------------------------- + +.. kernel-doc:: include/drm/drm_bridge.h + :internal: + +.. kernel-doc:: drivers/gpu/drm/drm_bridge.c + :export: + +Panel Helper Reference +====================== + +.. kernel-doc:: include/drm/drm_panel.h + :internal: + +.. kernel-doc:: drivers/gpu/drm/drm_panel.c + :export: + +.. kernel-doc:: drivers/gpu/drm/drm_panel.c + :doc: drm panel + Display Port Helper Functions Reference ======================================= @@ -158,9 +196,21 @@ MIPI DSI Helper Functions Reference .. kernel-doc:: drivers/gpu/drm/drm_mipi_dsi.c :export: +Output Probing Helper Functions Reference +========================================= + +.. kernel-doc:: drivers/gpu/drm/drm_probe_helper.c + :doc: output probing helper overview + +.. kernel-doc:: drivers/gpu/drm/drm_probe_helper.c + :export: + EDID Helper Functions Reference =============================== +.. kernel-doc:: include/drm/drm_edid.h + :internal: + .. kernel-doc:: drivers/gpu/drm/drm_edid.c :export: @@ -176,18 +226,6 @@ Rectangle Utilities Reference .. kernel-doc:: drivers/gpu/drm/drm_rect.c :export: -Flip-work Helper Reference -========================== - -.. kernel-doc:: include/drm/drm_flip_work.h - :doc: flip utils - -.. kernel-doc:: include/drm/drm_flip_work.h - :internal: - -.. kernel-doc:: drivers/gpu/drm/drm_flip_work.c - :export: - HDMI Infoframes Helper Reference ================================ @@ -202,59 +240,40 @@ libraries and hence is also included here. .. kernel-doc:: drivers/video/hdmi.c :export: -Plane Helper Reference -====================== - -.. kernel-doc:: drivers/gpu/drm/drm_plane_helper.c - :export: - -.. kernel-doc:: drivers/gpu/drm/drm_plane_helper.c - :doc: overview +Flip-work Helper Reference +========================== -Tile group ----------- +.. kernel-doc:: include/drm/drm_flip_work.h + :doc: flip utils -.. kernel-doc:: drivers/gpu/drm/drm_crtc.c - :doc: Tile group +.. kernel-doc:: include/drm/drm_flip_work.h + :internal: -Bridges -======= +.. kernel-doc:: drivers/gpu/drm/drm_flip_work.c + :export: -Overview --------- +Plane Helper Reference +====================== -.. kernel-doc:: drivers/gpu/drm/drm_bridge.c +.. kernel-doc:: drivers/gpu/drm/drm_plane_helper.c :doc: overview -Default bridge callback sequence --------------------------------- - -.. kernel-doc:: drivers/gpu/drm/drm_bridge.c - :doc: bridge callbacks - -.. kernel-doc:: drivers/gpu/drm/drm_bridge.c +.. kernel-doc:: drivers/gpu/drm/drm_plane_helper.c :export: -Panel Helper Reference -====================== - -.. kernel-doc:: include/drm/drm_panel.h - :internal: +Tile group +========== -.. kernel-doc:: drivers/gpu/drm/drm_panel.c - :export: +# FIXME: This should probably be moved into a property documentation section -.. kernel-doc:: drivers/gpu/drm/drm_panel.c - :doc: drm panel +.. kernel-doc:: drivers/gpu/drm/drm_crtc.c + :doc: Tile group -Simple KMS Helper Reference -=========================== +Auxiliary Modeset Helpers +========================= -.. kernel-doc:: include/drm/drm_simple_kms_helper.h - :internal: +.. kernel-doc:: drivers/gpu/drm/drm_modeset_helper.c + :doc: aux kms helpers -.. kernel-doc:: drivers/gpu/drm/drm_simple_kms_helper.c +.. kernel-doc:: drivers/gpu/drm/drm_modeset_helper.c :export: - -.. kernel-doc:: drivers/gpu/drm/drm_simple_kms_helper.c - :doc: overview diff --git a/Documentation/gpu/drm-kms.rst b/Documentation/gpu/drm-kms.rst index 8dfa4b214b96..53b872c105d2 100644 --- a/Documentation/gpu/drm-kms.rst +++ b/Documentation/gpu/drm-kms.rst @@ -2,9 +2,6 @@ Kernel Mode Setting (KMS) ========================= -Mode Setting -============ - 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>` @@ -18,60 +15,59 @@ be setup by initializing the following fields. - struct drm_mode_config_funcs \*funcs; Mode setting functions. -Display Modes Function Reference --------------------------------- +Modeset Base Object Abstraction +=============================== -.. kernel-doc:: include/drm/drm_modes.h +.. kernel-doc:: include/drm/drm_mode_object.h :internal: -.. kernel-doc:: drivers/gpu/drm/drm_modes.c +.. kernel-doc:: drivers/gpu/drm/drm_mode_object.c + :export: + +KMS Data Structures +=================== + +.. kernel-doc:: include/drm/drm_crtc.h + :internal: + +KMS API Functions +================= + +.. kernel-doc:: drivers/gpu/drm/drm_crtc.c :export: Atomic Mode Setting Function Reference --------------------------------------- +====================================== .. kernel-doc:: drivers/gpu/drm/drm_atomic.c :export: -.. kernel-doc:: drivers/gpu/drm/drm_atomic.c +.. kernel-doc:: include/drm/drm_atomic.h :internal: Frame Buffer Abstraction ------------------------- - -Frame buffers are abstract memory objects that provide a source of -pixels to scanout to a CRTC. Applications explicitly request the -creation of frame buffers through the DRM_IOCTL_MODE_ADDFB(2) ioctls -and receive an opaque handle that can be passed to the KMS CRTC control, -plane configuration and page flip functions. - -Frame buffers rely on the underneath memory manager for low-level memory -operations. When creating a frame buffer applications pass a memory -handle (or a list of memory handles for multi-planar formats) through -the ``drm_mode_fb_cmd2`` argument. For drivers using GEM as their -userspace buffer management interface this would be a GEM handle. -Drivers are however free to use their own backing storage object -handles, e.g. vmwgfx directly exposes special TTM handles to userspace -and so expects TTM handles in the create ioctl and not GEM handles. - -The lifetime of a drm framebuffer is controlled with a reference count, -drivers can grab additional references with -:c:func:`drm_framebuffer_reference()`and drop them again with -:c:func:`drm_framebuffer_unreference()`. For driver-private -framebuffers for which the last reference is never dropped (e.g. for the -fbdev framebuffer when the struct :c:type:`struct drm_framebuffer -<drm_framebuffer>` is embedded into the fbdev helper struct) -drivers can manually clean up a framebuffer at module unload time with -:c:func:`drm_framebuffer_unregister_private()`. +======================== + +.. kernel-doc:: drivers/gpu/drm/drm_framebuffer.c + :doc: overview + +Frame Buffer Functions Reference +-------------------------------- + +.. kernel-doc:: drivers/gpu/drm/drm_framebuffer.c + :export: + +.. kernel-doc:: include/drm/drm_framebuffer.h + :internal: DRM Format Handling -------------------- +=================== .. kernel-doc:: drivers/gpu/drm/drm_fourcc.c :export: Dumb Buffer Objects -------------------- +=================== The KMS API doesn't standardize backing storage object creation and leaves it to driver-specific ioctls. Furthermore actually creating a @@ -114,14 +110,59 @@ Note that dumb objects may not be used for gpu acceleration, as has been attempted on some ARM embedded platforms. Such drivers really must have a hardware-specific ioctl to allocate suitable buffer objects. -Output Polling --------------- +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: -void (\*output_poll_changed)(struct drm_device \*dev); -This operation notifies the driver that the status of one or more -connectors has changed. Drivers that use the fb helper can just call the -:c:func:`drm_fb_helper_hotplug_event()` function to handle this -operation. +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: + +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 ============================== @@ -151,250 +192,6 @@ 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. -Planes (:c:type:`struct drm_plane <drm_plane>`) ------------------------------------------------ - -A plane represents an image source that can be blended with or overlayed -on top of a CRTC during the scanout process. Planes are associated with -a frame buffer to crop a portion of the image memory (source) and -optionally scale it to a destination size. The result is then blended -with or overlayed on top of a CRTC. - -The DRM core recognizes three types of planes: - -- DRM_PLANE_TYPE_PRIMARY represents a "main" plane for a CRTC. - Primary planes are the planes operated upon by CRTC modesetting and - flipping operations described in the page_flip hook in - :c:type:`struct drm_crtc_funcs <drm_crtc_funcs>`. -- DRM_PLANE_TYPE_CURSOR represents a "cursor" plane for a CRTC. - Cursor planes are the planes operated upon by the - DRM_IOCTL_MODE_CURSOR and DRM_IOCTL_MODE_CURSOR2 ioctls. -- DRM_PLANE_TYPE_OVERLAY represents all non-primary, non-cursor - planes. Some drivers refer to these types of planes as "sprites" - internally. - -For compatibility with legacy userspace, only overlay planes are made -available to userspace by default. Userspace clients may set the -DRM_CLIENT_CAP_UNIVERSAL_PLANES client capability bit to indicate -that they wish to receive a universal plane list containing all plane -types. - -Plane Initialization -~~~~~~~~~~~~~~~~~~~~ - -To create a plane, a KMS drivers allocates and zeroes an instances of -:c:type:`struct drm_plane <drm_plane>` (possibly as part of a -larger structure) and registers it with a call to -:c:func:`drm_universal_plane_init()`. The function takes a -bitmask of the CRTCs that can be associated with the plane, a pointer to -the plane functions, a list of format supported formats, and the type of -plane (primary, cursor, or overlay) being initialized. - -Cursor and overlay planes are optional. All drivers should provide one -primary plane per CRTC (although this requirement may change in the -future); drivers that do not wish to provide special handling for -primary planes may make use of the helper functions described in ? to -create and register a primary plane with standard capabilities. - -Encoders (:c:type:`struct drm_encoder <drm_encoder>`) ------------------------------------------------------ - -An encoder takes pixel data from a CRTC and converts it to a format -suitable for any attached connectors. On some devices, it may be -possible to have a CRTC send data to more than one encoder. In that -case, both encoders would receive data from the same scanout buffer, -resulting in a "cloned" display configuration across the connectors -attached to each encoder. - -Encoder Initialization -~~~~~~~~~~~~~~~~~~~~~~ - -As for CRTCs, a KMS driver must create, initialize and register at least -one :c:type:`struct drm_encoder <drm_encoder>` instance. The -instance is allocated and zeroed by the driver, possibly as part of a -larger structure. - -Drivers must initialize the :c:type:`struct drm_encoder -<drm_encoder>` possible_crtcs and possible_clones fields before -registering the encoder. Both fields are bitmasks of respectively the -CRTCs that the encoder can be connected to, and sibling encoders -candidate for cloning. - -After being initialized, the encoder must be registered with a call to -:c:func:`drm_encoder_init()`. The function takes a pointer to the -encoder functions and an encoder type. Supported types are - -- DRM_MODE_ENCODER_DAC for VGA and analog on DVI-I/DVI-A -- DRM_MODE_ENCODER_TMDS for DVI, HDMI and (embedded) DisplayPort -- DRM_MODE_ENCODER_LVDS for display panels -- DRM_MODE_ENCODER_TVDAC for TV output (Composite, S-Video, - Component, SCART) -- DRM_MODE_ENCODER_VIRTUAL for virtual machine displays - -Encoders must be attached to a CRTC to be used. DRM drivers leave -encoders unattached at initialization time. Applications (or the fbdev -compatibility layer when implemented) are responsible for attaching the -encoders they want to use to a CRTC. - -Connectors (:c:type:`struct drm_connector <drm_connector>`) ------------------------------------------------------------ - -A connector is the final destination for pixel data on a device, and -usually connects directly to an external display device like a monitor -or laptop panel. A connector can only be attached to one encoder at a -time. The connector is also the structure where information about the -attached display is kept, so it contains fields for display data, EDID -data, DPMS & connection status, and information about modes supported on -the attached displays. - -Connector Initialization -~~~~~~~~~~~~~~~~~~~~~~~~ - -Finally a KMS driver must create, initialize, register and attach at -least one :c:type:`struct drm_connector <drm_connector>` -instance. The instance is created as other KMS objects and initialized -by setting the following fields. - -interlace_allowed - Whether the connector can handle interlaced modes. - -doublescan_allowed - Whether the connector can handle doublescan. - -display_info - Display information is filled from EDID information when a display - is detected. For non hot-pluggable displays such as flat panels in - embedded systems, the driver should initialize the - display_info.width_mm and display_info.height_mm fields with the - physical size of the display. - -polled - Connector polling mode, a combination of - - DRM_CONNECTOR_POLL_HPD - The connector generates hotplug events and doesn't need to be - periodically polled. The CONNECT and DISCONNECT flags must not - be set together with the HPD flag. - - DRM_CONNECTOR_POLL_CONNECT - Periodically poll the connector for connection. - - DRM_CONNECTOR_POLL_DISCONNECT - Periodically poll the connector for disconnection. - - Set to 0 for connectors that don't support connection status - discovery. - -The connector is then registered with a call to -:c:func:`drm_connector_init()` with a pointer to the connector -functions and a connector type, and exposed through sysfs with a call to -:c:func:`drm_connector_register()`. - -Supported connector types are - -- DRM_MODE_CONNECTOR_VGA -- DRM_MODE_CONNECTOR_DVII -- DRM_MODE_CONNECTOR_DVID -- DRM_MODE_CONNECTOR_DVIA -- DRM_MODE_CONNECTOR_Composite -- DRM_MODE_CONNECTOR_SVIDEO -- DRM_MODE_CONNECTOR_LVDS -- DRM_MODE_CONNECTOR_Component -- DRM_MODE_CONNECTOR_9PinDIN -- DRM_MODE_CONNECTOR_DisplayPort -- DRM_MODE_CONNECTOR_HDMIA -- DRM_MODE_CONNECTOR_HDMIB -- DRM_MODE_CONNECTOR_TV -- DRM_MODE_CONNECTOR_eDP -- DRM_MODE_CONNECTOR_VIRTUAL - -Connectors must be attached to an encoder to be used. For devices that -map connectors to encoders 1:1, the connector should be attached at -initialization time with a call to -:c:func:`drm_mode_connector_attach_encoder()`. The driver must -also set the :c:type:`struct drm_connector <drm_connector>` -encoder field to point to the attached encoder. - -Finally, drivers must initialize the connectors state change detection -with a call to :c:func:`drm_kms_helper_poll_init()`. If at least -one connector is pollable but can't generate hotplug interrupts -(indicated by the DRM_CONNECTOR_POLL_CONNECT and -DRM_CONNECTOR_POLL_DISCONNECT connector flags), a delayed work will -automatically be queued to periodically poll for changes. Connectors -that can generate hotplug interrupts must be marked with the -DRM_CONNECTOR_POLL_HPD flag instead, and their interrupt handler must -call :c:func:`drm_helper_hpd_irq_event()`. The function will -queue a delayed work to check the state of all connectors, but no -periodic polling will be done. - -Connector Operations -~~~~~~~~~~~~~~~~~~~~ - - **Note** - - Unless otherwise state, all operations are mandatory. - -DPMS -'''' - -void (\*dpms)(struct drm_connector \*connector, int mode); -The DPMS operation sets the power state of a connector. The mode -argument is one of - -- DRM_MODE_DPMS_ON - -- DRM_MODE_DPMS_STANDBY - -- DRM_MODE_DPMS_SUSPEND - -- DRM_MODE_DPMS_OFF - -In all but DPMS_ON mode the encoder to which the connector is attached -should put the display in low-power mode by driving its signals -appropriately. If more than one connector is attached to the encoder -care should be taken not to change the power state of other displays as -a side effect. Low-power mode should be propagated to the encoders and -CRTCs when all related connectors are put in low-power mode. - -Modes -''''' - -int (\*fill_modes)(struct drm_connector \*connector, uint32_t -max_width, uint32_t max_height); -Fill the mode list with all supported modes for the connector. If the -``max_width`` and ``max_height`` arguments are non-zero, the -implementation must ignore all modes wider than ``max_width`` or higher -than ``max_height``. - -The connector must also fill in this operation its display_info -width_mm and height_mm fields with the connected display physical size -in millimeters. The fields should be set to 0 if the value isn't known -or is not applicable (for instance for projector devices). - -Connection Status -''''''''''''''''' - -The connection status is updated through polling or hotplug events when -supported (see ?). The status value is reported to userspace through -ioctls and must not be used inside the driver, as it only gets -initialized by a call to :c:func:`drm_mode_getconnector()` from -userspace. - -enum drm_connector_status (\*detect)(struct drm_connector -\*connector, bool force); -Check to see if anything is attached to the connector. The ``force`` -parameter is set to false whilst polling or to true when checking the -connector due to user request. ``force`` can be used by the driver to -avoid expensive, destructive operations during automated probing. - -Return connector_status_connected if something is connected to the -connector, connector_status_disconnected if nothing is connected and -connector_status_unknown if the connection state isn't known. - -Drivers should only return connector_status_connected if the -connection status has really been probed as connected. Connectors that -can't detect the connection status, or failed connection status probes, -should return connector_status_unknown. Cleanup ------- @@ -463,20 +260,8 @@ 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 API Functions ------------------ - -.. kernel-doc:: drivers/gpu/drm/drm_crtc.c - :export: - -KMS Data Structures -------------------- - -.. kernel-doc:: include/drm/drm_crtc.h - :internal: - KMS Locking ------------ +=========== .. kernel-doc:: drivers/gpu/drm/drm_modeset_lock.c :doc: kms locking @@ -490,90 +275,38 @@ KMS Locking KMS Properties ============== -Drivers may need to expose additional parameters to applications than -those described in the previous sections. KMS supports attaching -properties to CRTCs, connectors and planes and offers a userspace API to -list, get and set the property values. - -Properties are identified by a name that uniquely defines the property -purpose, and store an associated value. For all property types except -blob properties the value is a 64-bit unsigned integer. - -KMS differentiates between properties and property instances. Drivers -first create properties and then create and associate individual -instances of those properties to objects. A property can be instantiated -multiple times and associated with different objects. Values are stored -in property instances, and all other property information are stored in -the property and shared between all instances of the property. - -Every property is created with a type that influences how the KMS core -handles the property. Supported property types are - -DRM_MODE_PROP_RANGE - Range properties report their minimum and maximum admissible values. - The KMS core verifies that values set by application fit in that - range. - -DRM_MODE_PROP_ENUM - Enumerated properties take a numerical value that ranges from 0 to - the number of enumerated values defined by the property minus one, - and associate a free-formed string name to each value. Applications - can retrieve the list of defined value-name pairs and use the - numerical value to get and set property instance values. - -DRM_MODE_PROP_BITMASK - Bitmask properties are enumeration properties that additionally - restrict all enumerated values to the 0..63 range. Bitmask property - instance values combine one or more of the enumerated bits defined - by the property. - -DRM_MODE_PROP_BLOB - Blob properties store a binary blob without any format restriction. - The binary blobs are created as KMS standalone objects, and blob - property instance values store the ID of their associated blob - object. - - Blob properties are only used for the connector EDID property and - cannot be created by drivers. - -To create a property drivers call one of the following functions -depending on the property type. All property creation functions take -property flags and name, as well as type-specific arguments. - -- struct drm_property \*drm_property_create_range(struct - drm_device \*dev, int flags, const char \*name, uint64_t min, - uint64_t max); - Create a range property with the given minimum and maximum values. - -- struct drm_property \*drm_property_create_enum(struct drm_device - \*dev, int flags, const char \*name, const struct - drm_prop_enum_list \*props, int num_values); - Create an enumerated property. The ``props`` argument points to an - array of ``num_values`` value-name pairs. - -- struct drm_property \*drm_property_create_bitmask(struct - drm_device \*dev, int flags, const char \*name, const struct - drm_prop_enum_list \*props, int num_values); - Create a bitmask property. The ``props`` argument points to an array - of ``num_values`` value-name pairs. - -Properties can additionally be created as immutable, in which case they -will be read-only for applications but can be modified by the driver. To -create an immutable property drivers must set the -DRM_MODE_PROP_IMMUTABLE flag at property creation time. - -When no array of value-name pairs is readily available at property -creation time for enumerated or range properties, drivers can create the -property using the :c:func:`drm_property_create()` function and -manually add enumeration value-name pairs by calling the -:c:func:`drm_property_add_enum()` function. Care must be taken to -properly specify the property type through the ``flags`` argument. - -After creating properties drivers can attach property instances to CRTC, -connector and plane objects by calling the -:c:func:`drm_object_attach_property()`. The function takes a -pointer to the target object, a pointer to the previously created -property and an initial instance value. +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: + +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:: include/drm/drm_color_mgmt.h + :internal: + +.. kernel-doc:: drivers/gpu/drm/drm_color_mgmt.c + :export: Existing KMS Properties ----------------------- diff --git a/Documentation/gpu/drm-mm.rst b/Documentation/gpu/drm-mm.rst index 59f9822fecd0..bca808535dfd 100644 --- a/Documentation/gpu/drm-mm.rst +++ b/Documentation/gpu/drm-mm.rst @@ -26,12 +26,12 @@ TTM, but has no video RAM management capabilities and is thus limited to UMA devices. The Translation Table Manager (TTM) ------------------------------------ +=================================== TTM design background and information belongs here. TTM initialization -~~~~~~~~~~~~~~~~~~ +------------------ **Warning** @@ -77,7 +77,7 @@ object, ttm_global_item_ref() is used to create an initial reference count for the TTM, which will call your initialization function. The Graphics Execution Manager (GEM) ------------------------------------- +==================================== The GEM design approach has resulted in a memory manager that doesn't provide full coverage of all (or even all common) use cases in its @@ -114,7 +114,7 @@ read & write, mapping, and domain ownership transfers are left to driver-specific ioctls. GEM Initialization -~~~~~~~~~~~~~~~~~~ +------------------ Drivers that use GEM must set the DRIVER_GEM bit in the struct :c:type:`struct drm_driver <drm_driver>` driver_features @@ -132,7 +132,7 @@ typically not managed by GEM, and must be initialized separately into its own DRM MM object. GEM Objects Creation -~~~~~~~~~~~~~~~~~~~~ +-------------------- GEM splits creation of GEM objects and allocation of the memory that backs them in two distinct operations. @@ -173,7 +173,7 @@ a call to :c:func:`drm_gem_private_object_init()` instead of must be managed by drivers. GEM Objects Lifetime -~~~~~~~~~~~~~~~~~~~~ +-------------------- All GEM objects are reference-counted by the GEM core. References can be acquired and release by :c:func:`calling @@ -196,7 +196,7 @@ resources created by the GEM core, which need to be released with :c:func:`drm_gem_object_release()`. GEM Objects Naming -~~~~~~~~~~~~~~~~~~ +------------------ Communication between userspace and the kernel refers to GEM objects using local handles, global names or, more recently, file descriptors. @@ -245,7 +245,7 @@ Furthermore PRIME also allows cross-device buffer sharing since it is based on dma-bufs. GEM Objects Mapping -~~~~~~~~~~~~~~~~~~~ +------------------- Because mapping operations are fairly heavyweight GEM favours read/write-like access to buffers, implemented through driver-specific @@ -304,7 +304,7 @@ Drivers that want to map the GEM object upfront instead of handling page faults can implement their own mmap file operation handler. Memory Coherency -~~~~~~~~~~~~~~~~ +---------------- When mapped to the device or used in a command buffer, backing pages for an object are flushed to memory and marked write combined so as to be @@ -320,7 +320,7 @@ blocks the client and waits for rendering to complete before performing any necessary flushing operations). Command Execution -~~~~~~~~~~~~~~~~~ +----------------- Perhaps the most important GEM function for GPU devices is providing a command execution interface to clients. Client programs construct @@ -348,8 +348,20 @@ GEM Function Reference .. kernel-doc:: include/drm/drm_gem.h :internal: +GEM CMA Helper Functions Reference +---------------------------------- + +.. kernel-doc:: drivers/gpu/drm/drm_gem_cma_helper.c + :doc: cma helpers + +.. kernel-doc:: drivers/gpu/drm/drm_gem_cma_helper.c + :export: + +.. kernel-doc:: include/drm/drm_gem_cma_helper.h + :internal: + VMA Offset Manager ------------------- +================== .. kernel-doc:: drivers/gpu/drm/drm_vma_manager.c :doc: vma offset manager @@ -361,14 +373,14 @@ VMA Offset Manager :internal: PRIME Buffer Sharing --------------------- +==================== PRIME is the cross device buffer sharing framework in drm, originally created for the OPTIMUS range of multi-gpu platforms. To userspace PRIME buffers are dma-buf based file descriptors. Overview and Driver Interface -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +----------------------------- Similar to GEM global names, PRIME file descriptors are also used to share buffer objects across processes. They offer additional security: @@ -406,7 +418,7 @@ struct drm_gem_object \*obj, int flags); struct drm_gem_object \* support PRIME. PRIME Helper Functions -~~~~~~~~~~~~~~~~~~~~~~ +---------------------- .. kernel-doc:: drivers/gpu/drm/drm_prime.c :doc: PRIME Helpers @@ -418,16 +430,16 @@ PRIME Function References :export: DRM MM Range Allocator ----------------------- +====================== Overview -~~~~~~~~ +-------- .. kernel-doc:: drivers/gpu/drm/drm_mm.c :doc: Overview LRU Scan/Eviction Support -~~~~~~~~~~~~~~~~~~~~~~~~~ +------------------------- .. kernel-doc:: drivers/gpu/drm/drm_mm.c :doc: lru scan roaster @@ -440,15 +452,3 @@ DRM MM Range Allocator Function References .. kernel-doc:: include/drm/drm_mm.h :internal: - -CMA Helper Functions Reference ------------------------------- - -.. kernel-doc:: drivers/gpu/drm/drm_gem_cma_helper.c - :doc: cma helpers - -.. kernel-doc:: drivers/gpu/drm/drm_gem_cma_helper.c - :export: - -.. kernel-doc:: include/drm/drm_gem_cma_helper.h - :internal: diff --git a/Documentation/gpu/drm-uapi.rst b/Documentation/gpu/drm-uapi.rst index 536bf3eaadd4..1ba301cebe16 100644 --- a/Documentation/gpu/drm-uapi.rst +++ b/Documentation/gpu/drm-uapi.rst @@ -33,6 +33,76 @@ Primary Nodes, DRM Master and Authentication .. kernel-doc:: include/drm/drm_auth.h :internal: +Open-Source Userspace Requirements +================================== + +The DRM subsystem has stricter requirements than most other kernel subsystems on +what the userspace side for new uAPI needs to look like. This section here +explains what exactly those requirements are, and why they exist. + +The short summary is that any addition of DRM uAPI requires corresponding +open-sourced userspace patches, and those patches must be reviewed and ready for +merging into a suitable and canonical upstream project. + +GFX devices (both display and render/GPU side) are really complex bits of +hardware, with userspace and kernel by necessity having to work together really +closely. The interfaces, for rendering and modesetting, must be extremely wide +and flexible, and therefore it is almost always impossible to precisely define +them for every possible corner case. This in turn makes it really practically +infeasible to differentiate between behaviour that's required by userspace, and +which must not be changed to avoid regressions, and behaviour which is only an +accidental artifact of the current implementation. + +Without access to the full source code of all userspace users that means it +becomes impossible to change the implementation details, since userspace could +depend upon the accidental behaviour of the current implementation in minute +details. And debugging such regressions without access to source code is pretty +much impossible. As a consequence this means: + +- The Linux kernel's "no regression" policy holds in practice only for + open-source userspace of the DRM subsystem. DRM developers are perfectly fine + if closed-source blob drivers in userspace use the same uAPI as the open + drivers, but they must do so in the exact same way as the open drivers. + Creative (ab)use of the interfaces will, and in the past routinely has, lead + to breakage. + +- Any new userspace interface must have an open-source implementation as + demonstration vehicle. + +The other reason for requiring open-source userspace is uAPI review. Since the +kernel and userspace parts of a GFX stack must work together so closely, code +review can only assess whether a new interface achieves its goals by looking at +both sides. Making sure that the interface indeed covers the use-case fully +leads to a few additional requirements: + +- The open-source userspace must not be a toy/test application, but the real + thing. Specifically it needs to handle all the usual error and corner cases. + These are often the places where new uAPI falls apart and hence essential to + assess the fitness of a proposed interface. + +- The userspace side must be fully reviewed and tested to the standards of that + userspace project. For e.g. mesa this means piglit testcases and review on the + mailing list. This is again to ensure that the new interface actually gets the + job done. + +- The userspace patches must be against the canonical upstream, not some vendor + fork. This is to make sure that no one cheats on the review and testing + requirements by doing a quick fork. + +- The kernel patch can only be merged after all the above requirements are met, + but it **must** be merged **before** the userspace patches land. uAPI always flows + from the kernel, doing things the other way round risks divergence of the uAPI + definitions and header files. + +These are fairly steep requirements, but have grown out from years of shared +pain and experience with uAPI added hastily, and almost always regretted about +just as fast. GFX devices change really fast, requiring a paradigm shift and +entire new set of uAPI interfaces every few years at least. Together with the +Linux kernel's guarantee to keep existing userspace running for 10+ years this +is already rather painful for the DRM subsystem, with multiple different uAPIs +for the same thing co-existing. If we add a few more complete mistakes into the +mix every year it would be entirely unmanageable. + Render nodes ============ @@ -86,6 +156,43 @@ other hand, a driver requires shared state between clients which is visible to user-space and accessible beyond open-file boundaries, they cannot support render nodes. +Validating changes with IGT +=========================== + +There's a collection of tests that aims to cover the whole functionality of +DRM drivers and that can be used to check that changes to DRM drivers or the +core don't regress existing functionality. This test suite is called IGT and +its code can be found in https://cgit.freedesktop.org/drm/igt-gpu-tools/. + +To build IGT, start by installing its build dependencies. In Debian-based +systems:: + + # apt-get build-dep intel-gpu-tools + +And in Fedora-based systems:: + + # dnf builddep intel-gpu-tools + +Then clone the repository:: + + $ git clone git://anongit.freedesktop.org/drm/igt-gpu-tools + +Configure the build system and start the build:: + + $ cd igt-gpu-tools && ./autogen.sh && make -j6 + +Download the piglit dependency:: + + $ ./scripts/run-tests.sh -d + +And run the tests:: + + $ ./scripts/run-tests.sh -t kms -t core -s + +run-tests.sh is a wrapper around piglit that will execute the tests matching +the -t options. A report in HTML format will be available in +./results/html/index.html. Results can be compared with piglit. + VBlank event handling ===================== diff --git a/Documentation/gpu/i915.rst b/Documentation/gpu/i915.rst index 2fe5952e90f1..87aaffc22920 100644 --- a/Documentation/gpu/i915.rst +++ b/Documentation/gpu/i915.rst @@ -70,6 +70,9 @@ Frontbuffer Tracking .. kernel-doc:: drivers/gpu/drm/i915/intel_frontbuffer.c :doc: frontbuffer tracking +.. kernel-doc:: drivers/gpu/drm/i915/intel_frontbuffer.h + :internal: + .. kernel-doc:: drivers/gpu/drm/i915/intel_frontbuffer.c :internal: diff --git a/Documentation/gpu/index.rst b/Documentation/gpu/index.rst index 5ff3d2b236af..be0dafcf5556 100644 --- a/Documentation/gpu/index.rst +++ b/Documentation/gpu/index.rst @@ -12,6 +12,7 @@ Linux GPU Driver Developer's Guide drm-uapi i915 vga-switcheroo + vgaarbiter .. only:: subproject diff --git a/Documentation/gpu/kms-properties.csv b/Documentation/gpu/kms-properties.csv index 4c5ce3edcfd9..981873a05d14 100644 --- a/Documentation/gpu/kms-properties.csv +++ b/Documentation/gpu/kms-properties.csv @@ -1,23 +1,10 @@ Owner Module/Drivers,Group,Property Name,Type,Property Values,Object attached,Description/Restrictions -DRM,Generic,“rotation”,BITMASK,"{ 0, ""rotate-0"" }, { 1, ""rotate-90"" }, { 2, ""rotate-180"" }, { 3, ""rotate-270"" }, { 4, ""reflect-x"" }, { 5, ""reflect-y"" }","CRTC, Plane",rotate-(degrees) rotates the image by the specified amount in degrees in counter clockwise direction. reflect-x and reflect-y reflects the image along the specified axis prior to rotation ,,“scaling mode”,ENUM,"{ ""None"", ""Full"", ""Center"", ""Full aspect"" }",Connector,"Supported by: amdgpu, gma500, i915, nouveau and radeon." ,Connector,“EDID”,BLOB | IMMUTABLE,0,Connector,Contains id of edid blob ptr object. ,,“DPMS”,ENUM,"{ “On”, “Standby”, “Suspend”, “Off” }",Connector,Contains DPMS operation mode value. ,,“PATH”,BLOB | IMMUTABLE,0,Connector,Contains topology path to a connector. ,,“TILE”,BLOB | IMMUTABLE,0,Connector,Contains tiling information for a connector. ,,“CRTC_ID”,OBJECT,DRM_MODE_OBJECT_CRTC,Connector,CRTC that connector is attached to (atomic) -,Plane,“type”,ENUM | IMMUTABLE,"{ ""Overlay"", ""Primary"", ""Cursor"" }",Plane,Plane type -,,“SRC_X”,RANGE,"Min=0, Max=UINT_MAX",Plane,Scanout source x coordinate in 16.16 fixed point (atomic) -,,“SRC_Y”,RANGE,"Min=0, Max=UINT_MAX",Plane,Scanout source y coordinate in 16.16 fixed point (atomic) -,,“SRC_W”,RANGE,"Min=0, Max=UINT_MAX",Plane,Scanout source width in 16.16 fixed point (atomic) -,,“SRC_H”,RANGE,"Min=0, Max=UINT_MAX",Plane,Scanout source height in 16.16 fixed point (atomic) -,,“CRTC_X”,SIGNED_RANGE,"Min=INT_MIN, Max=INT_MAX",Plane,Scanout CRTC (destination) x coordinate (atomic) -,,“CRTC_Y”,SIGNED_RANGE,"Min=INT_MIN, Max=INT_MAX",Plane,Scanout CRTC (destination) y coordinate (atomic) -,,“CRTC_W”,RANGE,"Min=0, Max=UINT_MAX",Plane,Scanout CRTC (destination) width (atomic) -,,“CRTC_H”,RANGE,"Min=0, Max=UINT_MAX",Plane,Scanout CRTC (destination) height (atomic) -,,“FB_ID”,OBJECT,DRM_MODE_OBJECT_FB,Plane,Scanout framebuffer (atomic) -,,“CRTC_ID”,OBJECT,DRM_MODE_OBJECT_CRTC,Plane,CRTC that plane is attached to (atomic) -,,“zpos”,RANGE,"Min=0, Max=UINT_MAX","Plane,Z-order of the plane.Planes with higher Z-order values are displayed on top, planes with identical Z-order values are display in an undefined order" ,DVI-I,“subconnector”,ENUM,"{ “Unknown”, “DVI-D”, “DVI-A” }",Connector,TBD ,,“select subconnector”,ENUM,"{ “Automatic”, “DVI-D”, “DVI-A” }",Connector,TBD ,TV,“subconnector”,ENUM,"{ ""Unknown"", ""Composite"", ""SVIDEO"", ""Component"", ""SCART"" }",Connector,TBD @@ -36,12 +23,6 @@ DRM,Generic,“rotation”,BITMASK,"{ 0, ""rotate-0"" }, { 1, ""rotate-90"" }, { ,Virtual GPU,“suggested X”,RANGE,"Min=0, Max=0xffffffff",Connector,property to suggest an X offset for a connector ,,“suggested Y”,RANGE,"Min=0, Max=0xffffffff",Connector,property to suggest an Y offset for a connector ,Optional,"""aspect ratio""",ENUM,"{ ""None"", ""4:3"", ""16:9"" }",Connector,TDB -,,“dirty”,ENUM | IMMUTABLE,"{ ""Off"", ""On"", ""Annotate"" }",Connector,TBD -,,“DEGAMMA_LUT”,BLOB,0,CRTC,DRM property to set the degamma lookup table (LUT) mapping pixel data from the framebuffer before it is given to the transformation matrix. The data is an interpreted as an array of struct drm_color_lut elements. Hardware might choose not to use the full precision of the LUT elements nor use all the elements of the LUT (for example the hardware might choose to interpolate between LUT[0] and LUT[4]). -,,“DEGAMMA_LUT_SIZE”,RANGE | IMMUTABLE,"Min=0, Max=UINT_MAX",CRTC,DRM property to gives the size of the lookup table to be set on the DEGAMMA_LUT property (the size depends on the underlying hardware). -,,“CTM”,BLOB,0,CRTC,DRM property to set the current transformation matrix (CTM) apply to pixel data after the lookup through the degamma LUT and before the lookup through the gamma LUT. The data is an interpreted as a struct drm_color_ctm. -,,“GAMMA_LUT”,BLOB,0,CRTC,DRM property to set the gamma lookup table (LUT) mapping pixel data after to the transformation matrix to data sent to the connector. The data is an interpreted as an array of struct drm_color_lut elements. Hardware might choose not to use the full precision of the LUT elements nor use all the elements of the LUT (for example the hardware might choose to interpolate between LUT[0] and LUT[4]). -,,“GAMMA_LUT_SIZE”,RANGE | IMMUTABLE,"Min=0, Max=UINT_MAX",CRTC,DRM property to gives the size of the lookup table to be set on the GAMMA_LUT property (the size depends on the underlying hardware). i915,Generic,"""Broadcast RGB""",ENUM,"{ ""Automatic"", ""Full"", ""Limited 16:235"" }",Connector,"When this property is set to Limited 16:235 and CTM is set, the hardware will be programmed with the result of the multiplication of CTM by the limited range matrix to ensure the pixels normaly in the range 0..1.0 are remapped to the range 16/255..235/255." ,,“audio”,ENUM,"{ ""force-dvi"", ""off"", ""auto"", ""on"" }",Connector,TBD ,SDVO-TV,“mode”,ENUM,"{ ""NTSC_M"", ""NTSC_J"", ""NTSC_443"", ""PAL_B"" } etc.",Connector,TBD @@ -95,7 +76,6 @@ armada,CRTC,"""CSC_YUV""",ENUM,"{ ""Auto"" , ""CCIR601"", ""CCIR709"" }",CRTC,TB ,,"""contrast""",RANGE,"Min=0, Max=0x7fff",Plane,TBD ,,"""saturation""",RANGE,"Min=0, Max=0x7fff",Plane,TBD exynos,CRTC,“mode”,ENUM,"{ ""normal"", ""blank"" }",CRTC,TBD -,Overlay,“zpos”,RANGE,"Min=0, Max=MAX_PLANE-1",Plane,TBD i2c/ch7006_drv,Generic,“scale”,RANGE,"Min=0, Max=2",Connector,TBD ,TV,“mode”,ENUM,"{ ""PAL"", ""PAL-M"",""PAL-N""}, ”PAL-Nc"" , ""PAL-60"", ""NTSC-M"", ""NTSC-J"" }",Connector,TBD nouveau,NV10 Overlay,"""colorkey""",RANGE,"Min=0, Max=0x01ffffff",Plane,TBD @@ -126,4 +106,3 @@ radeon,DVI-I,“coherent”,RANGE,"Min=0, Max=1",Connector,TBD ,FMT Dithering,“dither”,ENUM,"{ ""off"", ""on"" }",Connector,TBD rcar-du,Generic,"""alpha""",RANGE,"Min=0, Max=255",Plane,TBD ,,"""colorkey""",RANGE,"Min=0, Max=0x01ffffff",Plane,TBD -,,"""zpos""",RANGE,"Min=1, Max=7",Plane,TBD diff --git a/Documentation/gpu/vgaarbiter.rst b/Documentation/gpu/vgaarbiter.rst new file mode 100644 index 000000000000..0b41b051d021 --- /dev/null +++ b/Documentation/gpu/vgaarbiter.rst @@ -0,0 +1,191 @@ +=========== +VGA Arbiter +=========== + +Graphic devices are accessed through ranges in I/O or memory space. While most +modern devices allow relocation of such ranges, some "Legacy" VGA devices +implemented on PCI will typically have the same "hard-decoded" addresses as +they did on ISA. For more details see "PCI Bus Binding to IEEE Std 1275-1994 +Standard for Boot (Initialization Configuration) Firmware Revision 2.1" +Section 7, Legacy Devices. + +The Resource Access Control (RAC) module inside the X server [0] existed for +the legacy VGA arbitration task (besides other bus management tasks) when more +than one legacy device co-exists on the same machine. But the problem happens +when these devices are trying to be accessed by different userspace clients +(e.g. two server in parallel). Their address assignments conflict. Moreover, +ideally, being a userspace application, it is not the role of the X server to +control bus resources. Therefore an arbitration scheme outside of the X server +is needed to control the sharing of these resources. This document introduces +the operation of the VGA arbiter implemented for the Linux kernel. + +vgaarb kernel/userspace ABI +--------------------------- + +The vgaarb is a module of the Linux Kernel. When it is initially loaded, it +scans all PCI devices and adds the VGA ones inside the arbitration. The +arbiter then enables/disables the decoding on different devices of the VGA +legacy instructions. Devices which do not want/need to use the arbiter may +explicitly tell it by calling vga_set_legacy_decoding(). + +The kernel exports a char device interface (/dev/vga_arbiter) to the clients, +which has the following semantics: + +open + Opens a user instance of the arbiter. By default, it's attached to the + default VGA device of the system. + +close + Close a user instance. Release locks made by the user + +read + Return a string indicating the status of the target like: + + "<card_ID>,decodes=<io_state>,owns=<io_state>,locks=<io_state> (ic,mc)" + + An IO state string is of the form {io,mem,io+mem,none}, mc and + ic are respectively mem and io lock counts (for debugging/ + diagnostic only). "decodes" indicate what the card currently + decodes, "owns" indicates what is currently enabled on it, and + "locks" indicates what is locked by this card. If the card is + unplugged, we get "invalid" then for card_ID and an -ENODEV + error is returned for any command until a new card is targeted. + + +write + Write a command to the arbiter. List of commands: + + target <card_ID> + switch target to card <card_ID> (see below) + lock <io_state> + acquires locks on target ("none" is an invalid io_state) + trylock <io_state> + non-blocking acquire locks on target (returns EBUSY if + unsuccessful) + unlock <io_state> + release locks on target + unlock all + release all locks on target held by this user (not implemented + yet) + decodes <io_state> + set the legacy decoding attributes for the card + + poll + event if something changes on any card (not just the target) + + card_ID is of the form "PCI:domain:bus:dev.fn". It can be set to "default" + to go back to the system default card (TODO: not implemented yet). Currently, + only PCI is supported as a prefix, but the userland API may support other bus + types in the future, even if the current kernel implementation doesn't. + +Note about locks: + +The driver keeps track of which user has which locks on which card. It +supports stacking, like the kernel one. This complexifies the implementation +a bit, but makes the arbiter more tolerant to user space problems and able +to properly cleanup in all cases when a process dies. +Currently, a max of 16 cards can have locks simultaneously issued from +user space for a given user (file descriptor instance) of the arbiter. + +In the case of devices hot-{un,}plugged, there is a hook - pci_notify() - to +notify them being added/removed in the system and automatically added/removed +in the arbiter. + +There is also an in-kernel API of the arbiter in case DRM, vgacon, or other +drivers want to use it. + +In-kernel interface +------------------- + +.. kernel-doc:: include/linux/vgaarb.h + :internal: + +.. kernel-doc:: drivers/gpu/vga/vgaarb.c + :export: + +libpciaccess +------------ + +To use the vga arbiter char device it was implemented an API inside the +libpciaccess library. One field was added to struct pci_device (each device +on the system):: + + /* the type of resource decoded by the device */ + int vgaarb_rsrc; + +Besides it, in pci_system were added:: + + int vgaarb_fd; + int vga_count; + struct pci_device *vga_target; + struct pci_device *vga_default_dev; + +The vga_count is used to track how many cards are being arbitrated, so for +instance, if there is only one card, then it can completely escape arbitration. + +These functions below acquire VGA resources for the given card and mark those +resources as locked. If the resources requested are "normal" (and not legacy) +resources, the arbiter will first check whether the card is doing legacy +decoding for that type of resource. If yes, the lock is "converted" into a +legacy resource lock. The arbiter will first look for all VGA cards that +might conflict and disable their IOs and/or Memory access, including VGA +forwarding on P2P bridges if necessary, so that the requested resources can +be used. Then, the card is marked as locking these resources and the IO and/or +Memory access is enabled on the card (including VGA forwarding on parent +P2P bridges if any). In the case of vga_arb_lock(), the function will block +if some conflicting card is already locking one of the required resources (or +any resource on a different bus segment, since P2P bridges don't differentiate +VGA memory and IO afaik). If the card already owns the resources, the function +succeeds. vga_arb_trylock() will return (-EBUSY) instead of blocking. Nested +calls are supported (a per-resource counter is maintained). + +Set the target device of this client. :: + + int pci_device_vgaarb_set_target (struct pci_device *dev); + +For instance, in x86 if two devices on the same bus want to lock different +resources, both will succeed (lock). If devices are in different buses and +trying to lock different resources, only the first who tried succeeds. :: + + int pci_device_vgaarb_lock (void); + int pci_device_vgaarb_trylock (void); + +Unlock resources of device. :: + + int pci_device_vgaarb_unlock (void); + +Indicates to the arbiter if the card decodes legacy VGA IOs, legacy VGA +Memory, both, or none. All cards default to both, the card driver (fbdev for +example) should tell the arbiter if it has disabled legacy decoding, so the +card can be left out of the arbitration process (and can be safe to take +interrupts at any time. :: + + int pci_device_vgaarb_decodes (int new_vgaarb_rsrc); + +Connects to the arbiter device, allocates the struct :: + + int pci_device_vgaarb_init (void); + +Close the connection :: + + void pci_device_vgaarb_fini (void); + +xf86VGAArbiter (X server implementation) +---------------------------------------- + +X server basically wraps all the functions that touch VGA registers somehow. + +References +---------- + +Benjamin Herrenschmidt (IBM?) started this work when he discussed such design +with the Xorg community in 2005 [1, 2]. In the end of 2007, Paulo Zanoni and +Tiago Vignatti (both of C3SL/Federal University of Paraná) proceeded his work +enhancing the kernel code to adapt as a kernel module and also did the +implementation of the user space side [3]. Now (2009) Tiago Vignatti and Dave +Airlie finally put this work in shape and queued to Jesse Barnes' PCI tree. + +0) http://cgit.freedesktop.org/xorg/xserver/commit/?id=4b42448a2388d40f257774fbffdccaea87bd0347 +1) http://lists.freedesktop.org/archives/xorg/2005-March/006663.html +2) http://lists.freedesktop.org/archives/xorg/2005-March/006745.html +3) http://lists.freedesktop.org/archives/xorg/2007-October/029507.html |