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authorJesse Barnes <jbarnes@virtuousgeek.org>2009-10-26 16:06:31 -0400
committerDave Airlie <airlied@redhat.com>2010-04-20 18:12:11 -0400
commit2d2ef822758e3f5da59c40a392d0c6d89394d4b4 (patch)
tree95f99075fc8d67b2ccc99fa7c937c325c7e39a8a /Documentation/DocBook/drm.tmpl
parent10fd883ce384706f88554a0b08cc4d63345e7d8b (diff)
drm: add initial DRM developer documentation
Add a DRM DocBook providing basic information about DRM interfaces, including TTM, GEM, KMS and vblank infrastructure. Intended to provide information to new and existing developers about how to perform driver initialization, implement mode setting and other DRM features. Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org> Signed-off-by: Dave Airlie <airlied@redhat.com>
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1<?xml version="1.0" encoding="UTF-8"?>
2<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
3 "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
4
5<book id="drmDevelopersGuide">
6 <bookinfo>
7 <title>Linux DRM Developer's Guide</title>
8
9 <copyright>
10 <year>2008-2009</year>
11 <holder>
12 Intel Corporation (Jesse Barnes &lt;jesse.barnes@intel.com&gt;)
13 </holder>
14 </copyright>
15
16 <legalnotice>
17 <para>
18 The contents of this file may be used under the terms of the GNU
19 General Public License version 2 (the "GPL") as distributed in
20 the kernel source COPYING file.
21 </para>
22 </legalnotice>
23 </bookinfo>
24
25<toc></toc>
26
27 <!-- Introduction -->
28
29 <chapter id="drmIntroduction">
30 <title>Introduction</title>
31 <para>
32 The Linux DRM layer contains code intended to support the needs
33 of complex graphics devices, usually containing programmable
34 pipelines well suited to 3D graphics acceleration. Graphics
35 drivers in the kernel can make use of DRM functions to make
36 tasks like memory management, interrupt handling and DMA easier,
37 and provide a uniform interface to applications.
38 </para>
39 <para>
40 A note on versions: this guide covers features found in the DRM
41 tree, including the TTM memory manager, output configuration and
42 mode setting, and the new vblank internals, in addition to all
43 the regular features found in current kernels.
44 </para>
45 <para>
46 [Insert diagram of typical DRM stack here]
47 </para>
48 </chapter>
49
50 <!-- Internals -->
51
52 <chapter id="drmInternals">
53 <title>DRM Internals</title>
54 <para>
55 This chapter documents DRM internals relevant to driver authors
56 and developers working to add support for the latest features to
57 existing drivers.
58 </para>
59 <para>
60 First, we'll go over some typical driver initialization
61 requirements, like setting up command buffers, creating an
62 initial output configuration, and initializing core services.
63 Subsequent sections will cover core internals in more detail,
64 providing implementation notes and examples.
65 </para>
66 <para>
67 The DRM layer provides several services to graphics drivers,
68 many of them driven by the application interfaces it provides
69 through libdrm, the library that wraps most of the DRM ioctls.
70 These include vblank event handling, memory
71 management, output management, framebuffer management, command
72 submission &amp; fencing, suspend/resume support, and DMA
73 services.
74 </para>
75 <para>
76 The core of every DRM driver is struct drm_device. Drivers
77 will typically statically initialize a drm_device structure,
78 then pass it to drm_init() at load time.
79 </para>
80
81 <!-- Internals: driver init -->
82
83 <sect1>
84 <title>Driver initialization</title>
85 <para>
86 Before calling the DRM initialization routines, the driver must
87 first create and fill out a struct drm_device structure.
88 </para>
89 <programlisting>
90 static struct drm_driver driver = {
91 /* don't use mtrr's here, the Xserver or user space app should
92 * deal with them for intel hardware.
93 */
94 .driver_features =
95 DRIVER_USE_AGP | DRIVER_REQUIRE_AGP |
96 DRIVER_HAVE_IRQ | DRIVER_IRQ_SHARED | DRIVER_MODESET,
97 .load = i915_driver_load,
98 .unload = i915_driver_unload,
99 .firstopen = i915_driver_firstopen,
100 .lastclose = i915_driver_lastclose,
101 .preclose = i915_driver_preclose,
102 .save = i915_save,
103 .restore = i915_restore,
104 .device_is_agp = i915_driver_device_is_agp,
105 .get_vblank_counter = i915_get_vblank_counter,
106 .enable_vblank = i915_enable_vblank,
107 .disable_vblank = i915_disable_vblank,
108 .irq_preinstall = i915_driver_irq_preinstall,
109 .irq_postinstall = i915_driver_irq_postinstall,
110 .irq_uninstall = i915_driver_irq_uninstall,
111 .irq_handler = i915_driver_irq_handler,
112 .reclaim_buffers = drm_core_reclaim_buffers,
113 .get_map_ofs = drm_core_get_map_ofs,
114 .get_reg_ofs = drm_core_get_reg_ofs,
115 .fb_probe = intelfb_probe,
116 .fb_remove = intelfb_remove,
117 .fb_resize = intelfb_resize,
118 .master_create = i915_master_create,
119 .master_destroy = i915_master_destroy,
120#if defined(CONFIG_DEBUG_FS)
121 .debugfs_init = i915_debugfs_init,
122 .debugfs_cleanup = i915_debugfs_cleanup,
123#endif
124 .gem_init_object = i915_gem_init_object,
125 .gem_free_object = i915_gem_free_object,
126 .gem_vm_ops = &amp;i915_gem_vm_ops,
127 .ioctls = i915_ioctls,
128 .fops = {
129 .owner = THIS_MODULE,
130 .open = drm_open,
131 .release = drm_release,
132 .ioctl = drm_ioctl,
133 .mmap = drm_mmap,
134 .poll = drm_poll,
135 .fasync = drm_fasync,
136#ifdef CONFIG_COMPAT
137 .compat_ioctl = i915_compat_ioctl,
138#endif
139 },
140 .pci_driver = {
141 .name = DRIVER_NAME,
142 .id_table = pciidlist,
143 .probe = probe,
144 .remove = __devexit_p(drm_cleanup_pci),
145 },
146 .name = DRIVER_NAME,
147 .desc = DRIVER_DESC,
148 .date = DRIVER_DATE,
149 .major = DRIVER_MAJOR,
150 .minor = DRIVER_MINOR,
151 .patchlevel = DRIVER_PATCHLEVEL,
152 };
153 </programlisting>
154 <para>
155 In the example above, taken from the i915 DRM driver, the driver
156 sets several flags indicating what core features it supports.
157 We'll go over the individual callbacks in later sections. Since
158 flags indicate which features your driver supports to the DRM
159 core, you need to set most of them prior to calling drm_init(). Some,
160 like DRIVER_MODESET can be set later based on user supplied parameters,
161 but that's the exception rather than the rule.
162 </para>
163 <variablelist>
164 <title>Driver flags</title>
165 <varlistentry>
166 <term>DRIVER_USE_AGP</term>
167 <listitem><para>
168 Driver uses AGP interface
169 </para></listitem>
170 </varlistentry>
171 <varlistentry>
172 <term>DRIVER_REQUIRE_AGP</term>
173 <listitem><para>
174 Driver needs AGP interface to function.
175 </para></listitem>
176 </varlistentry>
177 <varlistentry>
178 <term>DRIVER_USE_MTRR</term>
179 <listitem>
180 <para>
181 Driver uses MTRR interface for mapping memory. Deprecated.
182 </para>
183 </listitem>
184 </varlistentry>
185 <varlistentry>
186 <term>DRIVER_PCI_DMA</term>
187 <listitem><para>
188 Driver is capable of PCI DMA. Deprecated.
189 </para></listitem>
190 </varlistentry>
191 <varlistentry>
192 <term>DRIVER_SG</term>
193 <listitem><para>
194 Driver can perform scatter/gather DMA. Deprecated.
195 </para></listitem>
196 </varlistentry>
197 <varlistentry>
198 <term>DRIVER_HAVE_DMA</term>
199 <listitem><para>Driver supports DMA. Deprecated.</para></listitem>
200 </varlistentry>
201 <varlistentry>
202 <term>DRIVER_HAVE_IRQ</term><term>DRIVER_IRQ_SHARED</term>
203 <listitem>
204 <para>
205 DRIVER_HAVE_IRQ indicates whether the driver has a IRQ
206 handler, DRIVER_IRQ_SHARED indicates whether the device &amp;
207 handler support shared IRQs (note that this is required of
208 PCI drivers).
209 </para>
210 </listitem>
211 </varlistentry>
212 <varlistentry>
213 <term>DRIVER_DMA_QUEUE</term>
214 <listitem>
215 <para>
216 If the driver queues DMA requests and completes them
217 asynchronously, this flag should be set. Deprecated.
218 </para>
219 </listitem>
220 </varlistentry>
221 <varlistentry>
222 <term>DRIVER_FB_DMA</term>
223 <listitem>
224 <para>
225 Driver supports DMA to/from the framebuffer. Deprecated.
226 </para>
227 </listitem>
228 </varlistentry>
229 <varlistentry>
230 <term>DRIVER_MODESET</term>
231 <listitem>
232 <para>
233 Driver supports mode setting interfaces.
234 </para>
235 </listitem>
236 </varlistentry>
237 </variablelist>
238 <para>
239 In this specific case, the driver requires AGP and supports
240 IRQs. DMA, as we'll see, is handled by device specific ioctls
241 in this case. It also supports the kernel mode setting APIs, though
242 unlike in the actual i915 driver source, this example unconditionally
243 exports KMS capability.
244 </para>
245 </sect1>
246
247 <!-- Internals: driver load -->
248
249 <sect1>
250 <title>Driver load</title>
251 <para>
252 In the previous section, we saw what a typical drm_driver
253 structure might look like. One of the more important fields in
254 the structure is the hook for the load function.
255 </para>
256 <programlisting>
257 static struct drm_driver driver = {
258 ...
259 .load = i915_driver_load,
260 ...
261 };
262 </programlisting>
263 <para>
264 The load function has many responsibilities: allocating a driver
265 private structure, specifying supported performance counters,
266 configuring the device (e.g. mapping registers &amp; command
267 buffers), initializing the memory manager, and setting up the
268 initial output configuration.
269 </para>
270 <para>
271 Note that the tasks performed at driver load time must not
272 conflict with DRM client requirements. For instance, if user
273 level mode setting drivers are in use, it would be problematic
274 to perform output discovery &amp; configuration at load time.
275 Likewise, if pre-memory management aware user level drivers are
276 in use, memory management and command buffer setup may need to
277 be omitted. These requirements are driver specific, and care
278 needs to be taken to keep both old and new applications and
279 libraries working. The i915 driver supports the "modeset"
280 module parameter to control whether advanced features are
281 enabled at load time or in legacy fashion. If compatibility is
282 a concern (e.g. with drivers converted over to the new interfaces
283 from the old ones), care must be taken to prevent incompatible
284 device initialization and control with the currently active
285 userspace drivers.
286 </para>
287
288 <sect2>
289 <title>Driver private &amp; performance counters</title>
290 <para>
291 The driver private hangs off the main drm_device structure and
292 can be used for tracking various device specific bits of
293 information, like register offsets, command buffer status,
294 register state for suspend/resume, etc. At load time, a
295 driver can simply allocate one and set drm_device.dev_priv
296 appropriately; at unload the driver can free it and set
297 drm_device.dev_priv to NULL.
298 </para>
299 <para>
300 The DRM supports several counters which can be used for rough
301 performance characterization. Note that the DRM stat counter
302 system is not often used by applications, and supporting
303 additional counters is completely optional.
304 </para>
305 <para>
306 These interfaces are deprecated and should not be used. If performance
307 monitoring is desired, the developer should investigate and
308 potentially enhance the kernel perf and tracing infrastructure to export
309 GPU related performance information to performance monitoring
310 tools and applications.
311 </para>
312 </sect2>
313
314 <sect2>
315 <title>Configuring the device</title>
316 <para>
317 Obviously, device configuration will be device specific.
318 However, there are several common operations: finding a
319 device's PCI resources, mapping them, and potentially setting
320 up an IRQ handler.
321 </para>
322 <para>
323 Finding &amp; mapping resources is fairly straightforward. The
324 DRM wrapper functions, drm_get_resource_start() and
325 drm_get_resource_len() can be used to find BARs on the given
326 drm_device struct. Once those values have been retrieved, the
327 driver load function can call drm_addmap() to create a new
328 mapping for the BAR in question. Note you'll probably want a
329 drm_local_map_t in your driver private structure to track any
330 mappings you create.
331<!-- !Fdrivers/gpu/drm/drm_bufs.c drm_get_resource_* -->
332<!-- !Finclude/drm/drmP.h drm_local_map_t -->
333 </para>
334 <para>
335 if compatibility with other operating systems isn't a concern
336 (DRM drivers can run under various BSD variants and OpenSolaris),
337 native Linux calls can be used for the above, e.g. pci_resource_*
338 and iomap*/iounmap. See the Linux device driver book for more
339 info.
340 </para>
341 <para>
342 Once you have a register map, you can use the DRM_READn() and
343 DRM_WRITEn() macros to access the registers on your device, or
344 use driver specific versions to offset into your MMIO space
345 relative to a driver specific base pointer (see I915_READ for
346 example).
347 </para>
348 <para>
349 If your device supports interrupt generation, you may want to
350 setup an interrupt handler at driver load time as well. This
351 is done using the drm_irq_install() function. If your device
352 supports vertical blank interrupts, it should call
353 drm_vblank_init() to initialize the core vblank handling code before
354 enabling interrupts on your device. This ensures the vblank related
355 structures are allocated and allows the core to handle vblank events.
356 </para>
357<!--!Fdrivers/char/drm/drm_irq.c drm_irq_install-->
358 <para>
359 Once your interrupt handler is registered (it'll use your
360 drm_driver.irq_handler as the actual interrupt handling
361 function), you can safely enable interrupts on your device,
362 assuming any other state your interrupt handler uses is also
363 initialized.
364 </para>
365 <para>
366 Another task that may be necessary during configuration is
367 mapping the video BIOS. On many devices, the VBIOS describes
368 device configuration, LCD panel timings (if any), and contains
369 flags indicating device state. Mapping the BIOS can be done
370 using the pci_map_rom() call, a convenience function that
371 takes care of mapping the actual ROM, whether it has been
372 shadowed into memory (typically at address 0xc0000) or exists
373 on the PCI device in the ROM BAR. Note that once you've
374 mapped the ROM and extracted any necessary information, be
375 sure to unmap it; on many devices the ROM address decoder is
376 shared with other BARs, so leaving it mapped can cause
377 undesired behavior like hangs or memory corruption.
378<!--!Fdrivers/pci/rom.c pci_map_rom-->
379 </para>
380 </sect2>
381
382 <sect2>
383 <title>Memory manager initialization</title>
384 <para>
385 In order to allocate command buffers, cursor memory, scanout
386 buffers, etc., as well as support the latest features provided
387 by packages like Mesa and the X.Org X server, your driver
388 should support a memory manager.
389 </para>
390 <para>
391 If your driver supports memory management (it should!), you'll
392 need to set that up at load time as well. How you intialize
393 it depends on which memory manager you're using, TTM or GEM.
394 </para>
395 <sect3>
396 <title>TTM initialization</title>
397 <para>
398 TTM (for Translation Table Manager) manages video memory and
399 aperture space for graphics devices. TTM supports both UMA devices
400 and devices with dedicated video RAM (VRAM), i.e. most discrete
401 graphics devices. If your device has dedicated RAM, supporting
402 TTM is desireable. TTM also integrates tightly with your
403 driver specific buffer execution function. See the radeon
404 driver for examples.
405 </para>
406 <para>
407 The core TTM structure is the ttm_bo_driver struct. It contains
408 several fields with function pointers for initializing the TTM,
409 allocating and freeing memory, waiting for command completion
410 and fence synchronization, and memory migration. See the
411 radeon_ttm.c file for an example of usage.
412 </para>
413 <para>
414 The ttm_global_reference structure is made up of several fields:
415 </para>
416 <programlisting>
417 struct ttm_global_reference {
418 enum ttm_global_types global_type;
419 size_t size;
420 void *object;
421 int (*init) (struct ttm_global_reference *);
422 void (*release) (struct ttm_global_reference *);
423 };
424 </programlisting>
425 <para>
426 There should be one global reference structure for your memory
427 manager as a whole, and there will be others for each object
428 created by the memory manager at runtime. Your global TTM should
429 have a type of TTM_GLOBAL_TTM_MEM. The size field for the global
430 object should be sizeof(struct ttm_mem_global), and the init and
431 release hooks should point at your driver specific init and
432 release routines, which will probably eventually call
433 ttm_mem_global_init and ttm_mem_global_release respectively.
434 </para>
435 <para>
436 Once your global TTM accounting structure is set up and initialized
437 (done by calling ttm_global_item_ref on the global object you
438 just created), you'll need to create a buffer object TTM to
439 provide a pool for buffer object allocation by clients and the
440 kernel itself. The type of this object should be TTM_GLOBAL_TTM_BO,
441 and its size should be sizeof(struct ttm_bo_global). Again,
442 driver specific init and release functions can be provided,
443 likely eventually calling ttm_bo_global_init and
444 ttm_bo_global_release, respectively. Also like the previous
445 object, ttm_global_item_ref is used to create an initial reference
446 count for the TTM, which will call your initalization function.
447 </para>
448 </sect3>
449 <sect3>
450 <title>GEM initialization</title>
451 <para>
452 GEM is an alternative to TTM, designed specifically for UMA
453 devices. It has simpler initialization and execution requirements
454 than TTM, but has no VRAM management capability. Core GEM
455 initialization is comprised of a basic drm_mm_init call to create
456 a GTT DRM MM object, which provides an address space pool for
457 object allocation. In a KMS configuration, the driver will
458 need to allocate and initialize a command ring buffer following
459 basic GEM initialization. Most UMA devices have a so-called
460 "stolen" memory region, which provides space for the initial
461 framebuffer and large, contiguous memory regions required by the
462 device. This space is not typically managed by GEM, and must
463 be initialized separately into its own DRM MM object.
464 </para>
465 <para>
466 Initialization will be driver specific, and will depend on
467 the architecture of the device. In the case of Intel
468 integrated graphics chips like 965GM, GEM initialization can
469 be done by calling the internal GEM init function,
470 i915_gem_do_init(). Since the 965GM is a UMA device
471 (i.e. it doesn't have dedicated VRAM), GEM will manage
472 making regular RAM available for GPU operations. Memory set
473 aside by the BIOS (called "stolen" memory by the i915
474 driver) will be managed by the DRM memrange allocator; the
475 rest of the aperture will be managed by GEM.
476 <programlisting>
477 /* Basic memrange allocator for stolen space (aka vram) */
478 drm_memrange_init(&amp;dev_priv->vram, 0, prealloc_size);
479 /* Let GEM Manage from end of prealloc space to end of aperture */
480 i915_gem_do_init(dev, prealloc_size, agp_size);
481 </programlisting>
482<!--!Edrivers/char/drm/drm_memrange.c-->
483 </para>
484 <para>
485 Once the memory manager has been set up, we can allocate the
486 command buffer. In the i915 case, this is also done with a
487 GEM function, i915_gem_init_ringbuffer().
488 </para>
489 </sect3>
490 </sect2>
491
492 <sect2>
493 <title>Output configuration</title>
494 <para>
495 The final initialization task is output configuration. This involves
496 finding and initializing the CRTCs, encoders and connectors
497 for your device, creating an initial configuration and
498 registering a framebuffer console driver.
499 </para>
500 <sect3>
501 <title>Output discovery and initialization</title>
502 <para>
503 Several core functions exist to create CRTCs, encoders and
504 connectors, namely drm_crtc_init(), drm_connector_init() and
505 drm_encoder_init(), along with several "helper" functions to
506 perform common tasks.
507 </para>
508 <para>
509 Connectors should be registered with sysfs once they've been
510 detected and initialized, using the
511 drm_sysfs_connector_add() function. Likewise, when they're
512 removed from the system, they should be destroyed with
513 drm_sysfs_connector_remove().
514 </para>
515 <programlisting>
516<![CDATA[
517void intel_crt_init(struct drm_device *dev)
518{
519 struct drm_connector *connector;
520 struct intel_output *intel_output;
521
522 intel_output = kzalloc(sizeof(struct intel_output), GFP_KERNEL);
523 if (!intel_output)
524 return;
525
526 connector = &intel_output->base;
527 drm_connector_init(dev, &intel_output->base,
528 &intel_crt_connector_funcs, DRM_MODE_CONNECTOR_VGA);
529
530 drm_encoder_init(dev, &intel_output->enc, &intel_crt_enc_funcs,
531 DRM_MODE_ENCODER_DAC);
532
533 drm_mode_connector_attach_encoder(&intel_output->base,
534 &intel_output->enc);
535
536 /* Set up the DDC bus. */
537 intel_output->ddc_bus = intel_i2c_create(dev, GPIOA, "CRTDDC_A");
538 if (!intel_output->ddc_bus) {
539 dev_printk(KERN_ERR, &dev->pdev->dev, "DDC bus registration "
540 "failed.\n");
541 return;
542 }
543
544 intel_output->type = INTEL_OUTPUT_ANALOG;
545 connector->interlace_allowed = 0;
546 connector->doublescan_allowed = 0;
547
548 drm_encoder_helper_add(&intel_output->enc, &intel_crt_helper_funcs);
549 drm_connector_helper_add(connector, &intel_crt_connector_helper_funcs);
550
551 drm_sysfs_connector_add(connector);
552}
553]]>
554 </programlisting>
555 <para>
556 In the example above (again, taken from the i915 driver), a
557 CRT connector and encoder combination is created. A device
558 specific i2c bus is also created, for fetching EDID data and
559 performing monitor detection. Once the process is complete,
560 the new connector is regsitered with sysfs, to make its
561 properties available to applications.
562 </para>
563 <sect4>
564 <title>Helper functions and core functions</title>
565 <para>
566 Since many PC-class graphics devices have similar display output
567 designs, the DRM provides a set of helper functions to make
568 output management easier. The core helper routines handle
569 encoder re-routing and disabling of unused functions following
570 mode set. Using the helpers is optional, but recommended for
571 devices with PC-style architectures (i.e. a set of display planes
572 for feeding pixels to encoders which are in turn routed to
573 connectors). Devices with more complex requirements needing
574 finer grained management can opt to use the core callbacks
575 directly.
576 </para>
577 <para>
578 [Insert typical diagram here.] [Insert OMAP style config here.]
579 </para>
580 </sect4>
581 <para>
582 For each encoder, CRTC and connector, several functions must
583 be provided, depending on the object type. Encoder objects
584 need should provide a DPMS (basically on/off) function, mode fixup
585 (for converting requested modes into native hardware timings),
586 and prepare, set and commit functions for use by the core DRM
587 helper functions. Connector helpers need to provide mode fetch and
588 validity functions as well as an encoder matching function for
589 returing an ideal encoder for a given connector. The core
590 connector functions include a DPMS callback, (deprecated)
591 save/restore routines, detection, mode probing, property handling,
592 and cleanup functions.
593 </para>
594<!--!Edrivers/char/drm/drm_crtc.h-->
595<!--!Edrivers/char/drm/drm_crtc.c-->
596<!--!Edrivers/char/drm/drm_crtc_helper.c-->
597 </sect3>
598 </sect2>
599 </sect1>
600
601 <!-- Internals: vblank handling -->
602
603 <sect1>
604 <title>VBlank event handling</title>
605 <para>
606 The DRM core exposes two vertical blank related ioctls:
607 DRM_IOCTL_WAIT_VBLANK and DRM_IOCTL_MODESET_CTL.
608<!--!Edrivers/char/drm/drm_irq.c-->
609 </para>
610 <para>
611 DRM_IOCTL_WAIT_VBLANK takes a struct drm_wait_vblank structure
612 as its argument, and is used to block or request a signal when a
613 specified vblank event occurs.
614 </para>
615 <para>
616 DRM_IOCTL_MODESET_CTL should be called by application level
617 drivers before and after mode setting, since on many devices the
618 vertical blank counter will be reset at that time. Internally,
619 the DRM snapshots the last vblank count when the ioctl is called
620 with the _DRM_PRE_MODESET command so that the counter won't go
621 backwards (which is dealt with when _DRM_POST_MODESET is used).
622 </para>
623 <para>
624 To support the functions above, the DRM core provides several
625 helper functions for tracking vertical blank counters, and
626 requires drivers to provide several callbacks:
627 get_vblank_counter(), enable_vblank() and disable_vblank(). The
628 core uses get_vblank_counter() to keep the counter accurate
629 across interrupt disable periods. It should return the current
630 vertical blank event count, which is often tracked in a device
631 register. The enable and disable vblank callbacks should enable
632 and disable vertical blank interrupts, respectively. In the
633 absence of DRM clients waiting on vblank events, the core DRM
634 code will use the disable_vblank() function to disable
635 interrupts, which saves power. They'll be re-enabled again when
636 a client calls the vblank wait ioctl above.
637 </para>
638 <para>
639 Devices that don't provide a count register can simply use an
640 internal atomic counter incremented on every vertical blank
641 interrupt, and can make their enable and disable vblank
642 functions into no-ops.
643 </para>
644 </sect1>
645
646 <sect1>
647 <title>Memory management</title>
648 <para>
649 The memory manager lies at the heart of many DRM operations, and
650 is also required to support advanced client features like OpenGL
651 pbuffers. The DRM currently contains two memory managers, TTM
652 and GEM.
653 </para>
654
655 <sect2>
656 <title>The Translation Table Manager (TTM)</title>
657 <para>
658 TTM was developed by Tungsten Graphics, primarily by Thomas
659 Hellström, and is intended to be a flexible, high performance
660 graphics memory manager.
661 </para>
662 <para>
663 Drivers wishing to support TTM must fill out a drm_bo_driver
664 structure.
665 </para>
666 <para>
667 TTM design background and information belongs here.
668 </para>
669 </sect2>
670
671 <sect2>
672 <title>The Graphics Execution Manager (GEM)</title>
673 <para>
674 GEM is an Intel project, authored by Eric Anholt and Keith
675 Packard. It provides simpler interfaces than TTM, and is well
676 suited for UMA devices.
677 </para>
678 <para>
679 GEM-enabled drivers must provide gem_init_object() and
680 gem_free_object() callbacks to support the core memory
681 allocation routines. They should also provide several driver
682 specific ioctls to support command execution, pinning, buffer
683 read &amp; write, mapping, and domain ownership transfers.
684 </para>
685 <para>
686 On a fundamental level, GEM involves several operations: memory
687 allocation and freeing, command execution, and aperture management
688 at command execution time. Buffer object allocation is relatively
689 straightforward and largely provided by Linux's shmem layer, which
690 provides memory to back each object. When mapped into the GTT
691 or used in a command buffer, the backing pages for an object are
692 flushed to memory and marked write combined so as to be coherent
693 with the GPU. Likewise, when the GPU finishes rendering to an object,
694 if the CPU accesses it, it must be made coherent with the CPU's view
695 of memory, usually involving GPU cache flushing of various kinds.
696 This core CPU&lt;-&gt;GPU coherency management is provided by the GEM
697 set domain function, which evaluates an object's current domain and
698 performs any necessary flushing or synchronization to put the object
699 into the desired coherency domain (note that the object may be busy,
700 i.e. an active render target; in that case the set domain function
701 will block the client and wait for rendering to complete before
702 performing any necessary flushing operations).
703 </para>
704 <para>
705 Perhaps the most important GEM function is providing a command
706 execution interface to clients. Client programs construct command
707 buffers containing references to previously allocated memory objects
708 and submit them to GEM. At that point, GEM will take care to bind
709 all the objects into the GTT, execute the buffer, and provide
710 necessary synchronization between clients accessing the same buffers.
711 This often involves evicting some objects from the GTT and re-binding
712 others (a fairly expensive operation), and providing relocation
713 support which hides fixed GTT offsets from clients. Clients must
714 take care not to submit command buffers that reference more objects
715 than can fit in the GTT or GEM will reject them and no rendering
716 will occur. Similarly, if several objects in the buffer require
717 fence registers to be allocated for correct rendering (e.g. 2D blits
718 on pre-965 chips), care must be taken not to require more fence
719 registers than are available to the client. Such resource management
720 should be abstracted from the client in libdrm.
721 </para>
722 </sect2>
723
724 </sect1>
725
726 <!-- Output management -->
727 <sect1>
728 <title>Output management</title>
729 <para>
730 At the core of the DRM output management code is a set of
731 structures representing CRTCs, encoders and connectors.
732 </para>
733 <para>
734 A CRTC is an abstraction representing a part of the chip that
735 contains a pointer to a scanout buffer. Therefore, the number
736 of CRTCs available determines how many independent scanout
737 buffers can be active at any given time. The CRTC structure
738 contains several fields to support this: a pointer to some video
739 memory, a display mode, and an (x, y) offset into the video
740 memory to support panning or configurations where one piece of
741 video memory spans multiple CRTCs.
742 </para>
743 <para>
744 An encoder takes pixel data from a CRTC and converts it to a
745 format suitable for any attached connectors. On some devices,
746 it may be possible to have a CRTC send data to more than one
747 encoder. In that case, both encoders would receive data from
748 the same scanout buffer, resulting in a "cloned" display
749 configuration across the connectors attached to each encoder.
750 </para>
751 <para>
752 A connector is the final destination for pixel data on a device,
753 and usually connects directly to an external display device like
754 a monitor or laptop panel. A connector can only be attached to
755 one encoder at a time. The connector is also the structure
756 where information about the attached display is kept, so it
757 contains fields for display data, EDID data, DPMS &amp;
758 connection status, and information about modes supported on the
759 attached displays.
760 </para>
761<!--!Edrivers/char/drm/drm_crtc.c-->
762 </sect1>
763
764 <sect1>
765 <title>Framebuffer management</title>
766 <para>
767 In order to set a mode on a given CRTC, encoder and connector
768 configuration, clients need to provide a framebuffer object which
769 will provide a source of pixels for the CRTC to deliver to the encoder(s)
770 and ultimately the connector(s) in the configuration. A framebuffer
771 is fundamentally a driver specific memory object, made into an opaque
772 handle by the DRM addfb function. Once an fb has been created this
773 way it can be passed to the KMS mode setting routines for use in
774 a configuration.
775 </para>
776 </sect1>
777
778 <sect1>
779 <title>Command submission &amp; fencing</title>
780 <para>
781 This should cover a few device specific command submission
782 implementations.
783 </para>
784 </sect1>
785
786 <sect1>
787 <title>Suspend/resume</title>
788 <para>
789 The DRM core provides some suspend/resume code, but drivers
790 wanting full suspend/resume support should provide save() and
791 restore() functions. These will be called at suspend,
792 hibernate, or resume time, and should perform any state save or
793 restore required by your device across suspend or hibernate
794 states.
795 </para>
796 </sect1>
797
798 <sect1>
799 <title>DMA services</title>
800 <para>
801 This should cover how DMA mapping etc. is supported by the core.
802 These functions are deprecated and should not be used.
803 </para>
804 </sect1>
805 </chapter>
806
807 <!-- External interfaces -->
808
809 <chapter id="drmExternals">
810 <title>Userland interfaces</title>
811 <para>
812 The DRM core exports several interfaces to applications,
813 generally intended to be used through corresponding libdrm
814 wrapper functions. In addition, drivers export device specific
815 interfaces for use by userspace drivers &amp; device aware
816 applications through ioctls and sysfs files.
817 </para>
818 <para>
819 External interfaces include: memory mapping, context management,
820 DMA operations, AGP management, vblank control, fence
821 management, memory management, and output management.
822 </para>
823 <para>
824 Cover generic ioctls and sysfs layout here. Only need high
825 level info, since man pages will cover the rest.
826 </para>
827 </chapter>
828
829 <!-- API reference -->
830
831 <appendix id="drmDriverApi">
832 <title>DRM Driver API</title>
833 <para>
834 Include auto-generated API reference here (need to reference it
835 from paragraphs above too).
836 </para>
837 </appendix>
838
839</book>
generated by cgit v1.2.2 (git 2.25.0) at 2024-12-20 22:04:29 -0500