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diff --git a/Documentation/gpu/drm-kms.rst b/Documentation/gpu/drm-kms.rst new file mode 100644 index 000000000000..8dfa4b214b96 --- /dev/null +++ b/Documentation/gpu/drm-kms.rst @@ -0,0 +1,653 @@ +========================= +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>` +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. + +Display Modes Function Reference +-------------------------------- + +.. kernel-doc:: include/drm/drm_modes.h + :internal: + +.. kernel-doc:: drivers/gpu/drm/drm_modes.c + :export: + +Atomic Mode Setting Function Reference +-------------------------------------- + +.. kernel-doc:: drivers/gpu/drm/drm_atomic.c + :export: + +.. kernel-doc:: drivers/gpu/drm/drm_atomic.c + :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()`. + +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 +buffer object even for GEM-based drivers is done through a +driver-specific ioctl - GEM only has a common userspace interface for +sharing and destroying objects. While not an issue for full-fledged +graphics stacks that include device-specific userspace components (in +libdrm for instance), this limit makes DRM-based early boot graphics +unnecessarily complex. + +Dumb objects partly alleviate the problem by providing a standard API to +create dumb buffers suitable for scanout, which can then be used to +create KMS frame buffers. + +To support dumb objects drivers must implement the dumb_create, +dumb_destroy and dumb_map_offset operations. + +- int (\*dumb_create)(struct drm_file \*file_priv, struct + drm_device \*dev, struct drm_mode_create_dumb \*args); + The dumb_create operation creates a driver object (GEM or TTM + handle) suitable for scanout based on the width, height and depth + from the struct :c:type:`struct drm_mode_create_dumb + <drm_mode_create_dumb>` argument. It fills the argument's + handle, pitch and size fields with a handle for the newly created + object and its line pitch and size in bytes. + +- int (\*dumb_destroy)(struct drm_file \*file_priv, struct + drm_device \*dev, uint32_t handle); + The dumb_destroy operation destroys a dumb object created by + dumb_create. + +- int (\*dumb_map_offset)(struct drm_file \*file_priv, struct + drm_device \*dev, uint32_t handle, uint64_t \*offset); + The dumb_map_offset operation associates an mmap fake offset with + the object given by the handle and returns it. Drivers must use the + :c:func:`drm_gem_create_mmap_offset()` function to associate + the fake offset as described in ?. + +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 +-------------- + +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. + +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. + +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 +------- + +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 +------------------------------------------- + +:: + + 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_mode_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 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 + +.. kernel-doc:: include/drm/drm_modeset_lock.h + :internal: + +.. kernel-doc:: drivers/gpu/drm/drm_modeset_lock.c + :export: + +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. + +Existing KMS Properties +----------------------- + +The following table gives description of drm properties exposed by +various modules/drivers. + +.. csv-table:: + :header-rows: 1 + :file: kms-properties.csv + +Vertical Blanking +================= + +Vertical blanking plays a major role in graphics rendering. To achieve +tear-free display, users must synchronize page flips and/or rendering to +vertical blanking. The DRM API offers ioctls to perform page flips +synchronized to vertical blanking and wait for vertical blanking. + +The DRM core handles most of the vertical blanking management logic, +which involves filtering out spurious interrupts, keeping race-free +blanking counters, coping with counter wrap-around and resets and +keeping use counts. It relies on the driver to generate vertical +blanking interrupts and optionally provide a hardware vertical blanking +counter. Drivers must implement the following operations. + +- int (\*enable_vblank) (struct drm_device \*dev, int crtc); void + (\*disable_vblank) (struct drm_device \*dev, int crtc); + Enable or disable vertical blanking interrupts for the given CRTC. + +- u32 (\*get_vblank_counter) (struct drm_device \*dev, int crtc); + Retrieve the value of the vertical blanking counter for the given + CRTC. If the hardware maintains a vertical blanking counter its value + should be returned. Otherwise drivers can use the + :c:func:`drm_vblank_count()` helper function to handle this + operation. + +Drivers must initialize the vertical blanking handling core with a call +to :c:func:`drm_vblank_init()` in their load operation. + +Vertical blanking interrupts can be enabled by the DRM core or by +drivers themselves (for instance to handle page flipping operations). +The DRM core maintains a vertical blanking use count to ensure that the +interrupts are not disabled while a user still needs them. To increment +the use count, drivers call :c:func:`drm_vblank_get()`. Upon +return vertical blanking interrupts are guaranteed to be enabled. + +To decrement the use count drivers call +:c:func:`drm_vblank_put()`. Only when the use count drops to zero +will the DRM core disable the vertical blanking interrupts after a delay +by scheduling a timer. The delay is accessible through the +vblankoffdelay module parameter or the ``drm_vblank_offdelay`` global +variable and expressed in milliseconds. Its default value is 5000 ms. +Zero means never disable, and a negative value means disable +immediately. Drivers may override the behaviour by setting the +:c:type:`struct drm_device <drm_device>` +vblank_disable_immediate flag, which when set causes vblank interrupts +to be disabled immediately regardless of the drm_vblank_offdelay +value. The flag should only be set if there's a properly working +hardware vblank counter present. + +When a vertical blanking interrupt occurs drivers only need to call the +:c:func:`drm_handle_vblank()` function to account for the +interrupt. + +Resources allocated by :c:func:`drm_vblank_init()` must be freed +with a call to :c:func:`drm_vblank_cleanup()` in the driver unload +operation handler. + +Vertical Blanking and Interrupt Handling Functions Reference +------------------------------------------------------------ + +.. kernel-doc:: drivers/gpu/drm/drm_irq.c + :export: + +.. kernel-doc:: include/drm/drm_irq.h + :internal: |