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.
18 Modeset Base Object Abstraction
19 ===============================
21 .. kernel-doc:: include/drm/drm_mode_object.h
24 .. kernel-doc:: drivers/gpu/drm/drm_mode_object.c
30 .. kernel-doc:: include/drm/drm_crtc.h
36 .. kernel-doc:: drivers/gpu/drm/drm_crtc.c
39 Atomic Mode Setting Function Reference
40 ======================================
42 .. kernel-doc:: drivers/gpu/drm/drm_atomic.c
45 .. kernel-doc:: include/drm/drm_atomic.h
48 Frame Buffer Abstraction
49 ========================
51 .. kernel-doc:: drivers/gpu/drm/drm_framebuffer.c
54 Frame Buffer Functions Reference
55 --------------------------------
57 .. kernel-doc:: drivers/gpu/drm/drm_framebuffer.c
60 .. kernel-doc:: include/drm/drm_framebuffer.h
66 .. kernel-doc:: drivers/gpu/drm/drm_fourcc.c
72 The KMS API doesn't standardize backing storage object creation and
73 leaves it to driver-specific ioctls. Furthermore actually creating a
74 buffer object even for GEM-based drivers is done through a
75 driver-specific ioctl - GEM only has a common userspace interface for
76 sharing and destroying objects. While not an issue for full-fledged
77 graphics stacks that include device-specific userspace components (in
78 libdrm for instance), this limit makes DRM-based early boot graphics
79 unnecessarily complex.
81 Dumb objects partly alleviate the problem by providing a standard API to
82 create dumb buffers suitable for scanout, which can then be used to
83 create KMS frame buffers.
85 To support dumb objects drivers must implement the dumb_create,
86 dumb_destroy and dumb_map_offset operations.
88 - int (\*dumb_create)(struct drm_file \*file_priv, struct
89 drm_device \*dev, struct drm_mode_create_dumb \*args);
90 The dumb_create operation creates a driver object (GEM or TTM
91 handle) suitable for scanout based on the width, height and depth
92 from the struct :c:type:`struct drm_mode_create_dumb
93 <drm_mode_create_dumb>` argument. It fills the argument's
94 handle, pitch and size fields with a handle for the newly created
95 object and its line pitch and size in bytes.
97 - int (\*dumb_destroy)(struct drm_file \*file_priv, struct
98 drm_device \*dev, uint32_t handle);
99 The dumb_destroy operation destroys a dumb object created by
102 - int (\*dumb_map_offset)(struct drm_file \*file_priv, struct
103 drm_device \*dev, uint32_t handle, uint64_t \*offset);
104 The dumb_map_offset operation associates an mmap fake offset with
105 the object given by the handle and returns it. Drivers must use the
106 :c:func:`drm_gem_create_mmap_offset()` function to associate
107 the fake offset as described in ?.
109 Note that dumb objects may not be used for gpu acceleration, as has been
110 attempted on some ARM embedded platforms. Such drivers really must have
111 a hardware-specific ioctl to allocate suitable buffer objects.
116 Plane Functions Reference
117 -------------------------
119 .. kernel-doc:: include/drm/drm_plane.h
122 .. kernel-doc:: drivers/gpu/drm/drm_plane.c
125 Display Modes Function Reference
126 ================================
128 .. kernel-doc:: include/drm/drm_modes.h
131 .. kernel-doc:: drivers/gpu/drm/drm_modes.c
134 Connector Abstraction
135 =====================
137 .. kernel-doc:: drivers/gpu/drm/drm_connector.c
140 Connector Functions Reference
141 -----------------------------
143 .. kernel-doc:: include/drm/drm_connector.h
146 .. kernel-doc:: drivers/gpu/drm/drm_connector.c
152 .. kernel-doc:: drivers/gpu/drm/drm_encoder.c
155 Encoder Functions Reference
156 ---------------------------
158 .. kernel-doc:: include/drm/drm_encoder.h
161 .. kernel-doc:: drivers/gpu/drm/drm_encoder.c
164 KMS Initialization and Cleanup
165 ==============================
167 A KMS device is abstracted and exposed as a set of planes, CRTCs,
168 encoders and connectors. KMS drivers must thus create and initialize all
169 those objects at load time after initializing mode setting.
171 CRTCs (:c:type:`struct drm_crtc <drm_crtc>`)
172 --------------------------------------------
174 A CRTC is an abstraction representing a part of the chip that contains a
175 pointer to a scanout buffer. Therefore, the number of CRTCs available
176 determines how many independent scanout buffers can be active at any
177 given time. The CRTC structure contains several fields to support this:
178 a pointer to some video memory (abstracted as a frame buffer object), a
179 display mode, and an (x, y) offset into the video memory to support
180 panning or configurations where one piece of video memory spans multiple
186 A KMS device must create and register at least one struct
187 :c:type:`struct drm_crtc <drm_crtc>` instance. The instance is
188 allocated and zeroed by the driver, possibly as part of a larger
189 structure, and registered with a call to :c:func:`drm_crtc_init()`
190 with a pointer to CRTC functions.
192 Planes (:c:type:`struct drm_plane <drm_plane>`)
193 -----------------------------------------------
195 A plane represents an image source that can be blended with or overlayed
196 on top of a CRTC during the scanout process. Planes are associated with
197 a frame buffer to crop a portion of the image memory (source) and
198 optionally scale it to a destination size. The result is then blended
199 with or overlayed on top of a CRTC.
201 The DRM core recognizes three types of planes:
203 - DRM_PLANE_TYPE_PRIMARY represents a "main" plane for a CRTC.
204 Primary planes are the planes operated upon by CRTC modesetting and
205 flipping operations described in the page_flip hook in
206 :c:type:`struct drm_crtc_funcs <drm_crtc_funcs>`.
207 - DRM_PLANE_TYPE_CURSOR represents a "cursor" plane for a CRTC.
208 Cursor planes are the planes operated upon by the
209 DRM_IOCTL_MODE_CURSOR and DRM_IOCTL_MODE_CURSOR2 ioctls.
210 - DRM_PLANE_TYPE_OVERLAY represents all non-primary, non-cursor
211 planes. Some drivers refer to these types of planes as "sprites"
214 For compatibility with legacy userspace, only overlay planes are made
215 available to userspace by default. Userspace clients may set the
216 DRM_CLIENT_CAP_UNIVERSAL_PLANES client capability bit to indicate
217 that they wish to receive a universal plane list containing all plane
223 To create a plane, a KMS drivers allocates and zeroes an instances of
224 :c:type:`struct drm_plane <drm_plane>` (possibly as part of a
225 larger structure) and registers it with a call to
226 :c:func:`drm_universal_plane_init()`. The function takes a
227 bitmask of the CRTCs that can be associated with the plane, a pointer to
228 the plane functions, a list of format supported formats, and the type of
229 plane (primary, cursor, or overlay) being initialized.
231 Cursor and overlay planes are optional. All drivers should provide one
232 primary plane per CRTC (although this requirement may change in the
233 future); drivers that do not wish to provide special handling for
234 primary planes may make use of the helper functions described in ? to
235 create and register a primary plane with standard capabilities.
240 The DRM core manages its objects' lifetime. When an object is not needed
241 anymore the core calls its destroy function, which must clean up and
242 free every resource allocated for the object. Every
243 :c:func:`drm_\*_init()` call must be matched with a corresponding
244 :c:func:`drm_\*_cleanup()` call to cleanup CRTCs
245 (:c:func:`drm_crtc_cleanup()`), planes
246 (:c:func:`drm_plane_cleanup()`), encoders
247 (:c:func:`drm_encoder_cleanup()`) and connectors
248 (:c:func:`drm_connector_cleanup()`). Furthermore, connectors that
249 have been added to sysfs must be removed by a call to
250 :c:func:`drm_connector_unregister()` before calling
251 :c:func:`drm_connector_cleanup()`.
253 Connectors state change detection must be cleanup up with a call to
254 :c:func:`drm_kms_helper_poll_fini()`.
256 Output discovery and initialization example
257 -------------------------------------------
261 void intel_crt_init(struct drm_device *dev)
263 struct drm_connector *connector;
264 struct intel_output *intel_output;
266 intel_output = kzalloc(sizeof(struct intel_output), GFP_KERNEL);
270 connector = &intel_output->base;
271 drm_connector_init(dev, &intel_output->base,
272 &intel_crt_connector_funcs, DRM_MODE_CONNECTOR_VGA);
274 drm_encoder_init(dev, &intel_output->enc, &intel_crt_enc_funcs,
275 DRM_MODE_ENCODER_DAC);
277 drm_mode_connector_attach_encoder(&intel_output->base,
280 /* Set up the DDC bus. */
281 intel_output->ddc_bus = intel_i2c_create(dev, GPIOA, "CRTDDC_A");
282 if (!intel_output->ddc_bus) {
283 dev_printk(KERN_ERR, &dev->pdev->dev, "DDC bus registration "
288 intel_output->type = INTEL_OUTPUT_ANALOG;
289 connector->interlace_allowed = 0;
290 connector->doublescan_allowed = 0;
292 drm_encoder_helper_add(&intel_output->enc, &intel_crt_helper_funcs);
293 drm_connector_helper_add(connector, &intel_crt_connector_helper_funcs);
295 drm_connector_register(connector);
298 In the example above (taken from the i915 driver), a CRTC, connector and
299 encoder combination is created. A device-specific i2c bus is also
300 created for fetching EDID data and performing monitor detection. Once
301 the process is complete, the new connector is registered with sysfs to
302 make its properties available to applications.
307 .. kernel-doc:: drivers/gpu/drm/drm_modeset_lock.c
310 .. kernel-doc:: include/drm/drm_modeset_lock.h
313 .. kernel-doc:: drivers/gpu/drm/drm_modeset_lock.c
319 Property Types and Blob Property Support
320 ----------------------------------------
322 .. kernel-doc:: drivers/gpu/drm/drm_property.c
325 .. kernel-doc:: include/drm/drm_property.h
328 .. kernel-doc:: drivers/gpu/drm/drm_property.c
331 Blending and Z-Position properties
332 ----------------------------------
334 .. kernel-doc:: drivers/gpu/drm/drm_blend.c
337 Existing KMS Properties
338 -----------------------
340 The following table gives description of drm properties exposed by
341 various modules/drivers.
345 :file: kms-properties.csv
350 Vertical blanking plays a major role in graphics rendering. To achieve
351 tear-free display, users must synchronize page flips and/or rendering to
352 vertical blanking. The DRM API offers ioctls to perform page flips
353 synchronized to vertical blanking and wait for vertical blanking.
355 The DRM core handles most of the vertical blanking management logic,
356 which involves filtering out spurious interrupts, keeping race-free
357 blanking counters, coping with counter wrap-around and resets and
358 keeping use counts. It relies on the driver to generate vertical
359 blanking interrupts and optionally provide a hardware vertical blanking
360 counter. Drivers must implement the following operations.
362 - int (\*enable_vblank) (struct drm_device \*dev, int crtc); void
363 (\*disable_vblank) (struct drm_device \*dev, int crtc);
364 Enable or disable vertical blanking interrupts for the given CRTC.
366 - u32 (\*get_vblank_counter) (struct drm_device \*dev, int crtc);
367 Retrieve the value of the vertical blanking counter for the given
368 CRTC. If the hardware maintains a vertical blanking counter its value
369 should be returned. Otherwise drivers can use the
370 :c:func:`drm_vblank_count()` helper function to handle this
373 Drivers must initialize the vertical blanking handling core with a call
374 to :c:func:`drm_vblank_init()` in their load operation.
376 Vertical blanking interrupts can be enabled by the DRM core or by
377 drivers themselves (for instance to handle page flipping operations).
378 The DRM core maintains a vertical blanking use count to ensure that the
379 interrupts are not disabled while a user still needs them. To increment
380 the use count, drivers call :c:func:`drm_vblank_get()`. Upon
381 return vertical blanking interrupts are guaranteed to be enabled.
383 To decrement the use count drivers call
384 :c:func:`drm_vblank_put()`. Only when the use count drops to zero
385 will the DRM core disable the vertical blanking interrupts after a delay
386 by scheduling a timer. The delay is accessible through the
387 vblankoffdelay module parameter or the ``drm_vblank_offdelay`` global
388 variable and expressed in milliseconds. Its default value is 5000 ms.
389 Zero means never disable, and a negative value means disable
390 immediately. Drivers may override the behaviour by setting the
391 :c:type:`struct drm_device <drm_device>`
392 vblank_disable_immediate flag, which when set causes vblank interrupts
393 to be disabled immediately regardless of the drm_vblank_offdelay
394 value. The flag should only be set if there's a properly working
395 hardware vblank counter present.
397 When a vertical blanking interrupt occurs drivers only need to call the
398 :c:func:`drm_handle_vblank()` function to account for the
401 Resources allocated by :c:func:`drm_vblank_init()` must be freed
402 with a call to :c:func:`drm_vblank_cleanup()` in the driver unload
405 Vertical Blanking and Interrupt Handling Functions Reference
406 ------------------------------------------------------------
408 .. kernel-doc:: drivers/gpu/drm/drm_irq.c
411 .. kernel-doc:: include/drm/drm_irq.h