1 =========================
2 Kernel Mode Setting (KMS)
3 =========================
5 Drivers must initialize the mode setting core by calling
6 :c:func:`drm_mode_config_init()` on the DRM device. The function
7 initializes the :c:type:`struct drm_device <drm_device>`
8 mode_config field and never fails. Once done, mode configuration must
9 be setup by initializing the following fields.
11 - int min_width, min_height; int max_width, max_height;
12 Minimum and maximum width and height of the frame buffers in pixel
15 - struct drm_mode_config_funcs \*funcs;
16 Mode setting functions.
21 .. kernel-doc:: include/drm/drm_crtc.h
27 .. kernel-doc:: drivers/gpu/drm/drm_crtc.c
30 Atomic Mode Setting Function Reference
31 ======================================
33 .. kernel-doc:: drivers/gpu/drm/drm_atomic.c
36 .. kernel-doc:: include/drm/drm_atomic.h
39 Frame Buffer Abstraction
40 ========================
42 .. kernel-doc:: drivers/gpu/drm/drm_framebuffer.c
45 Frame Buffer Functions Reference
46 --------------------------------
48 .. kernel-doc:: drivers/gpu/drm/drm_framebuffer.c
51 .. kernel-doc:: include/drm/drm_framebuffer.h
57 .. kernel-doc:: drivers/gpu/drm/drm_fourcc.c
63 The KMS API doesn't standardize backing storage object creation and
64 leaves it to driver-specific ioctls. Furthermore actually creating a
65 buffer object even for GEM-based drivers is done through a
66 driver-specific ioctl - GEM only has a common userspace interface for
67 sharing and destroying objects. While not an issue for full-fledged
68 graphics stacks that include device-specific userspace components (in
69 libdrm for instance), this limit makes DRM-based early boot graphics
70 unnecessarily complex.
72 Dumb objects partly alleviate the problem by providing a standard API to
73 create dumb buffers suitable for scanout, which can then be used to
74 create KMS frame buffers.
76 To support dumb objects drivers must implement the dumb_create,
77 dumb_destroy and dumb_map_offset operations.
79 - int (\*dumb_create)(struct drm_file \*file_priv, struct
80 drm_device \*dev, struct drm_mode_create_dumb \*args);
81 The dumb_create operation creates a driver object (GEM or TTM
82 handle) suitable for scanout based on the width, height and depth
83 from the struct :c:type:`struct drm_mode_create_dumb
84 <drm_mode_create_dumb>` argument. It fills the argument's
85 handle, pitch and size fields with a handle for the newly created
86 object and its line pitch and size in bytes.
88 - int (\*dumb_destroy)(struct drm_file \*file_priv, struct
89 drm_device \*dev, uint32_t handle);
90 The dumb_destroy operation destroys a dumb object created by
93 - int (\*dumb_map_offset)(struct drm_file \*file_priv, struct
94 drm_device \*dev, uint32_t handle, uint64_t \*offset);
95 The dumb_map_offset operation associates an mmap fake offset with
96 the object given by the handle and returns it. Drivers must use the
97 :c:func:`drm_gem_create_mmap_offset()` function to associate
98 the fake offset as described in ?.
100 Note that dumb objects may not be used for gpu acceleration, as has been
101 attempted on some ARM embedded platforms. Such drivers really must have
102 a hardware-specific ioctl to allocate suitable buffer objects.
104 Display Modes Function Reference
105 ================================
107 .. kernel-doc:: include/drm/drm_modes.h
110 .. kernel-doc:: drivers/gpu/drm/drm_modes.c
113 Connector Abstraction
114 =====================
116 .. kernel-doc:: drivers/gpu/drm/drm_connector.c
119 Connector Functions Reference
120 -----------------------------
122 .. kernel-doc:: include/drm/drm_connector.h
125 .. kernel-doc:: drivers/gpu/drm/drm_connector.c
128 KMS Initialization and Cleanup
129 ==============================
131 A KMS device is abstracted and exposed as a set of planes, CRTCs,
132 encoders and connectors. KMS drivers must thus create and initialize all
133 those objects at load time after initializing mode setting.
135 CRTCs (:c:type:`struct drm_crtc <drm_crtc>`)
136 --------------------------------------------
138 A CRTC is an abstraction representing a part of the chip that contains a
139 pointer to a scanout buffer. Therefore, the number of CRTCs available
140 determines how many independent scanout buffers can be active at any
141 given time. The CRTC structure contains several fields to support this:
142 a pointer to some video memory (abstracted as a frame buffer object), a
143 display mode, and an (x, y) offset into the video memory to support
144 panning or configurations where one piece of video memory spans multiple
150 A KMS device must create and register at least one struct
151 :c:type:`struct drm_crtc <drm_crtc>` instance. The instance is
152 allocated and zeroed by the driver, possibly as part of a larger
153 structure, and registered with a call to :c:func:`drm_crtc_init()`
154 with a pointer to CRTC functions.
156 Planes (:c:type:`struct drm_plane <drm_plane>`)
157 -----------------------------------------------
159 A plane represents an image source that can be blended with or overlayed
160 on top of a CRTC during the scanout process. Planes are associated with
161 a frame buffer to crop a portion of the image memory (source) and
162 optionally scale it to a destination size. The result is then blended
163 with or overlayed on top of a CRTC.
165 The DRM core recognizes three types of planes:
167 - DRM_PLANE_TYPE_PRIMARY represents a "main" plane for a CRTC.
168 Primary planes are the planes operated upon by CRTC modesetting and
169 flipping operations described in the page_flip hook in
170 :c:type:`struct drm_crtc_funcs <drm_crtc_funcs>`.
171 - DRM_PLANE_TYPE_CURSOR represents a "cursor" plane for a CRTC.
172 Cursor planes are the planes operated upon by the
173 DRM_IOCTL_MODE_CURSOR and DRM_IOCTL_MODE_CURSOR2 ioctls.
174 - DRM_PLANE_TYPE_OVERLAY represents all non-primary, non-cursor
175 planes. Some drivers refer to these types of planes as "sprites"
178 For compatibility with legacy userspace, only overlay planes are made
179 available to userspace by default. Userspace clients may set the
180 DRM_CLIENT_CAP_UNIVERSAL_PLANES client capability bit to indicate
181 that they wish to receive a universal plane list containing all plane
187 To create a plane, a KMS drivers allocates and zeroes an instances of
188 :c:type:`struct drm_plane <drm_plane>` (possibly as part of a
189 larger structure) and registers it with a call to
190 :c:func:`drm_universal_plane_init()`. The function takes a
191 bitmask of the CRTCs that can be associated with the plane, a pointer to
192 the plane functions, a list of format supported formats, and the type of
193 plane (primary, cursor, or overlay) being initialized.
195 Cursor and overlay planes are optional. All drivers should provide one
196 primary plane per CRTC (although this requirement may change in the
197 future); drivers that do not wish to provide special handling for
198 primary planes may make use of the helper functions described in ? to
199 create and register a primary plane with standard capabilities.
201 Encoders (:c:type:`struct drm_encoder <drm_encoder>`)
202 -----------------------------------------------------
204 An encoder takes pixel data from a CRTC and converts it to a format
205 suitable for any attached connectors. On some devices, it may be
206 possible to have a CRTC send data to more than one encoder. In that
207 case, both encoders would receive data from the same scanout buffer,
208 resulting in a "cloned" display configuration across the connectors
209 attached to each encoder.
211 Encoder Initialization
212 ~~~~~~~~~~~~~~~~~~~~~~
214 As for CRTCs, a KMS driver must create, initialize and register at least
215 one :c:type:`struct drm_encoder <drm_encoder>` instance. The
216 instance is allocated and zeroed by the driver, possibly as part of a
219 Drivers must initialize the :c:type:`struct drm_encoder
220 <drm_encoder>` possible_crtcs and possible_clones fields before
221 registering the encoder. Both fields are bitmasks of respectively the
222 CRTCs that the encoder can be connected to, and sibling encoders
223 candidate for cloning.
225 After being initialized, the encoder must be registered with a call to
226 :c:func:`drm_encoder_init()`. The function takes a pointer to the
227 encoder functions and an encoder type. Supported types are
229 - DRM_MODE_ENCODER_DAC for VGA and analog on DVI-I/DVI-A
230 - DRM_MODE_ENCODER_TMDS for DVI, HDMI and (embedded) DisplayPort
231 - DRM_MODE_ENCODER_LVDS for display panels
232 - DRM_MODE_ENCODER_TVDAC for TV output (Composite, S-Video,
234 - DRM_MODE_ENCODER_VIRTUAL for virtual machine displays
236 Encoders must be attached to a CRTC to be used. DRM drivers leave
237 encoders unattached at initialization time. Applications (or the fbdev
238 compatibility layer when implemented) are responsible for attaching the
239 encoders they want to use to a CRTC.
244 The DRM core manages its objects' lifetime. When an object is not needed
245 anymore the core calls its destroy function, which must clean up and
246 free every resource allocated for the object. Every
247 :c:func:`drm_\*_init()` call must be matched with a corresponding
248 :c:func:`drm_\*_cleanup()` call to cleanup CRTCs
249 (:c:func:`drm_crtc_cleanup()`), planes
250 (:c:func:`drm_plane_cleanup()`), encoders
251 (:c:func:`drm_encoder_cleanup()`) and connectors
252 (:c:func:`drm_connector_cleanup()`). Furthermore, connectors that
253 have been added to sysfs must be removed by a call to
254 :c:func:`drm_connector_unregister()` before calling
255 :c:func:`drm_connector_cleanup()`.
257 Connectors state change detection must be cleanup up with a call to
258 :c:func:`drm_kms_helper_poll_fini()`.
260 Output discovery and initialization example
261 -------------------------------------------
265 void intel_crt_init(struct drm_device *dev)
267 struct drm_connector *connector;
268 struct intel_output *intel_output;
270 intel_output = kzalloc(sizeof(struct intel_output), GFP_KERNEL);
274 connector = &intel_output->base;
275 drm_connector_init(dev, &intel_output->base,
276 &intel_crt_connector_funcs, DRM_MODE_CONNECTOR_VGA);
278 drm_encoder_init(dev, &intel_output->enc, &intel_crt_enc_funcs,
279 DRM_MODE_ENCODER_DAC);
281 drm_mode_connector_attach_encoder(&intel_output->base,
284 /* Set up the DDC bus. */
285 intel_output->ddc_bus = intel_i2c_create(dev, GPIOA, "CRTDDC_A");
286 if (!intel_output->ddc_bus) {
287 dev_printk(KERN_ERR, &dev->pdev->dev, "DDC bus registration "
292 intel_output->type = INTEL_OUTPUT_ANALOG;
293 connector->interlace_allowed = 0;
294 connector->doublescan_allowed = 0;
296 drm_encoder_helper_add(&intel_output->enc, &intel_crt_helper_funcs);
297 drm_connector_helper_add(connector, &intel_crt_connector_helper_funcs);
299 drm_connector_register(connector);
302 In the example above (taken from the i915 driver), a CRTC, connector and
303 encoder combination is created. A device-specific i2c bus is also
304 created for fetching EDID data and performing monitor detection. Once
305 the process is complete, the new connector is registered with sysfs to
306 make its properties available to applications.
311 .. kernel-doc:: drivers/gpu/drm/drm_modeset_lock.c
314 .. kernel-doc:: include/drm/drm_modeset_lock.h
317 .. kernel-doc:: drivers/gpu/drm/drm_modeset_lock.c
323 Drivers may need to expose additional parameters to applications than
324 those described in the previous sections. KMS supports attaching
325 properties to CRTCs, connectors and planes and offers a userspace API to
326 list, get and set the property values.
328 Properties are identified by a name that uniquely defines the property
329 purpose, and store an associated value. For all property types except
330 blob properties the value is a 64-bit unsigned integer.
332 KMS differentiates between properties and property instances. Drivers
333 first create properties and then create and associate individual
334 instances of those properties to objects. A property can be instantiated
335 multiple times and associated with different objects. Values are stored
336 in property instances, and all other property information are stored in
337 the property and shared between all instances of the property.
339 Every property is created with a type that influences how the KMS core
340 handles the property. Supported property types are
343 Range properties report their minimum and maximum admissible values.
344 The KMS core verifies that values set by application fit in that
348 Enumerated properties take a numerical value that ranges from 0 to
349 the number of enumerated values defined by the property minus one,
350 and associate a free-formed string name to each value. Applications
351 can retrieve the list of defined value-name pairs and use the
352 numerical value to get and set property instance values.
354 DRM_MODE_PROP_BITMASK
355 Bitmask properties are enumeration properties that additionally
356 restrict all enumerated values to the 0..63 range. Bitmask property
357 instance values combine one or more of the enumerated bits defined
361 Blob properties store a binary blob without any format restriction.
362 The binary blobs are created as KMS standalone objects, and blob
363 property instance values store the ID of their associated blob
366 Blob properties are only used for the connector EDID property and
367 cannot be created by drivers.
369 To create a property drivers call one of the following functions
370 depending on the property type. All property creation functions take
371 property flags and name, as well as type-specific arguments.
373 - struct drm_property \*drm_property_create_range(struct
374 drm_device \*dev, int flags, const char \*name, uint64_t min,
376 Create a range property with the given minimum and maximum values.
378 - struct drm_property \*drm_property_create_enum(struct drm_device
379 \*dev, int flags, const char \*name, const struct
380 drm_prop_enum_list \*props, int num_values);
381 Create an enumerated property. The ``props`` argument points to an
382 array of ``num_values`` value-name pairs.
384 - struct drm_property \*drm_property_create_bitmask(struct
385 drm_device \*dev, int flags, const char \*name, const struct
386 drm_prop_enum_list \*props, int num_values);
387 Create a bitmask property. The ``props`` argument points to an array
388 of ``num_values`` value-name pairs.
390 Properties can additionally be created as immutable, in which case they
391 will be read-only for applications but can be modified by the driver. To
392 create an immutable property drivers must set the
393 DRM_MODE_PROP_IMMUTABLE flag at property creation time.
395 When no array of value-name pairs is readily available at property
396 creation time for enumerated or range properties, drivers can create the
397 property using the :c:func:`drm_property_create()` function and
398 manually add enumeration value-name pairs by calling the
399 :c:func:`drm_property_add_enum()` function. Care must be taken to
400 properly specify the property type through the ``flags`` argument.
402 After creating properties drivers can attach property instances to CRTC,
403 connector and plane objects by calling the
404 :c:func:`drm_object_attach_property()`. The function takes a
405 pointer to the target object, a pointer to the previously created
406 property and an initial instance value.
408 Blending and Z-Position properties
409 ----------------------------------
411 .. kernel-doc:: drivers/gpu/drm/drm_blend.c
414 Existing KMS Properties
415 -----------------------
417 The following table gives description of drm properties exposed by
418 various modules/drivers.
422 :file: kms-properties.csv
427 Vertical blanking plays a major role in graphics rendering. To achieve
428 tear-free display, users must synchronize page flips and/or rendering to
429 vertical blanking. The DRM API offers ioctls to perform page flips
430 synchronized to vertical blanking and wait for vertical blanking.
432 The DRM core handles most of the vertical blanking management logic,
433 which involves filtering out spurious interrupts, keeping race-free
434 blanking counters, coping with counter wrap-around and resets and
435 keeping use counts. It relies on the driver to generate vertical
436 blanking interrupts and optionally provide a hardware vertical blanking
437 counter. Drivers must implement the following operations.
439 - int (\*enable_vblank) (struct drm_device \*dev, int crtc); void
440 (\*disable_vblank) (struct drm_device \*dev, int crtc);
441 Enable or disable vertical blanking interrupts for the given CRTC.
443 - u32 (\*get_vblank_counter) (struct drm_device \*dev, int crtc);
444 Retrieve the value of the vertical blanking counter for the given
445 CRTC. If the hardware maintains a vertical blanking counter its value
446 should be returned. Otherwise drivers can use the
447 :c:func:`drm_vblank_count()` helper function to handle this
450 Drivers must initialize the vertical blanking handling core with a call
451 to :c:func:`drm_vblank_init()` in their load operation.
453 Vertical blanking interrupts can be enabled by the DRM core or by
454 drivers themselves (for instance to handle page flipping operations).
455 The DRM core maintains a vertical blanking use count to ensure that the
456 interrupts are not disabled while a user still needs them. To increment
457 the use count, drivers call :c:func:`drm_vblank_get()`. Upon
458 return vertical blanking interrupts are guaranteed to be enabled.
460 To decrement the use count drivers call
461 :c:func:`drm_vblank_put()`. Only when the use count drops to zero
462 will the DRM core disable the vertical blanking interrupts after a delay
463 by scheduling a timer. The delay is accessible through the
464 vblankoffdelay module parameter or the ``drm_vblank_offdelay`` global
465 variable and expressed in milliseconds. Its default value is 5000 ms.
466 Zero means never disable, and a negative value means disable
467 immediately. Drivers may override the behaviour by setting the
468 :c:type:`struct drm_device <drm_device>`
469 vblank_disable_immediate flag, which when set causes vblank interrupts
470 to be disabled immediately regardless of the drm_vblank_offdelay
471 value. The flag should only be set if there's a properly working
472 hardware vblank counter present.
474 When a vertical blanking interrupt occurs drivers only need to call the
475 :c:func:`drm_handle_vblank()` function to account for the
478 Resources allocated by :c:func:`drm_vblank_init()` must be freed
479 with a call to :c:func:`drm_vblank_cleanup()` in the driver unload
482 Vertical Blanking and Interrupt Handling Functions Reference
483 ------------------------------------------------------------
485 .. kernel-doc:: drivers/gpu/drm/drm_irq.c
488 .. kernel-doc:: include/drm/drm_irq.h