1 ============= 1 =============
2 DRM Internals 2 DRM Internals
3 ============= 3 =============
4 4
5 This chapter documents DRM internals relevant 5 This chapter documents DRM internals relevant to driver authors and
6 developers working to add support for the late 6 developers working to add support for the latest features to existing
7 drivers. 7 drivers.
8 8
9 First, we go over some typical driver initiali 9 First, we go over some typical driver initialization requirements, like
10 setting up command buffers, creating an initia 10 setting up command buffers, creating an initial output configuration,
11 and initializing core services. Subsequent sec 11 and initializing core services. Subsequent sections cover core internals
12 in more detail, providing implementation notes 12 in more detail, providing implementation notes and examples.
13 13
14 The DRM layer provides several services to gra 14 The DRM layer provides several services to graphics drivers, many of
15 them driven by the application interfaces it p 15 them driven by the application interfaces it provides through libdrm,
16 the library that wraps most of the DRM ioctls. 16 the library that wraps most of the DRM ioctls. These include vblank
17 event handling, memory management, output mana 17 event handling, memory management, output management, framebuffer
18 management, command submission & fencing, susp 18 management, command submission & fencing, suspend/resume support, and
19 DMA services. 19 DMA services.
20 20
21 Driver Initialization 21 Driver Initialization
22 ===================== 22 =====================
23 23
24 At the core of every DRM driver is a :c:type:` 24 At the core of every DRM driver is a :c:type:`struct drm_driver
25 <drm_driver>` structure. Drivers typically sta 25 <drm_driver>` structure. Drivers typically statically initialize
26 a drm_driver structure, and then pass it to 26 a drm_driver structure, and then pass it to
27 drm_dev_alloc() to allocate a device instance. 27 drm_dev_alloc() to allocate a device instance. After the
28 device instance is fully initialized it can be 28 device instance is fully initialized it can be registered (which makes
29 it accessible from userspace) using drm_dev_re 29 it accessible from userspace) using drm_dev_register().
30 30
31 The :c:type:`struct drm_driver <drm_driver>` s 31 The :c:type:`struct drm_driver <drm_driver>` structure
32 contains static information that describes the 32 contains static information that describes the driver and features it
33 supports, and pointers to methods that the DRM 33 supports, and pointers to methods that the DRM core will call to
34 implement the DRM API. We will first go throug 34 implement the DRM API. We will first go through the :c:type:`struct
35 drm_driver <drm_driver>` static information fi 35 drm_driver <drm_driver>` static information fields, and will
36 then describe individual operations in details 36 then describe individual operations in details as they get used in later
37 sections. 37 sections.
38 38
39 Driver Information 39 Driver Information
40 ------------------ 40 ------------------
41 41
42 Major, Minor and Patchlevel 42 Major, Minor and Patchlevel
43 ~~~~~~~~~~~~~~~~~~~~~~~~~~~ 43 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
44 44
45 int major; int minor; int patchlevel; 45 int major; int minor; int patchlevel;
46 The DRM core identifies driver versions by a m 46 The DRM core identifies driver versions by a major, minor and patch
47 level triplet. The information is printed to t 47 level triplet. The information is printed to the kernel log at
48 initialization time and passed to userspace th 48 initialization time and passed to userspace through the
49 DRM_IOCTL_VERSION ioctl. 49 DRM_IOCTL_VERSION ioctl.
50 50
51 The major and minor numbers are also used to v 51 The major and minor numbers are also used to verify the requested driver
52 API version passed to DRM_IOCTL_SET_VERSION. W 52 API version passed to DRM_IOCTL_SET_VERSION. When the driver API
53 changes between minor versions, applications c 53 changes between minor versions, applications can call
54 DRM_IOCTL_SET_VERSION to select a specific ver 54 DRM_IOCTL_SET_VERSION to select a specific version of the API. If the
55 requested major isn't equal to the driver majo 55 requested major isn't equal to the driver major, or the requested minor
56 is larger than the driver minor, the DRM_IOCTL 56 is larger than the driver minor, the DRM_IOCTL_SET_VERSION call will
57 return an error. Otherwise the driver's set_ve 57 return an error. Otherwise the driver's set_version() method will be
58 called with the requested version. 58 called with the requested version.
59 59
60 Name and Description !! 60 Name, Description and Date
61 ~~~~~~~~~~~~~~~~~~~~ !! 61 ~~~~~~~~~~~~~~~~~~~~~~~~~~
62 62
63 char \*name; char \*desc; char \*date; 63 char \*name; char \*desc; char \*date;
64 The driver name is printed to the kernel log a 64 The driver name is printed to the kernel log at initialization time,
65 used for IRQ registration and passed to usersp 65 used for IRQ registration and passed to userspace through
66 DRM_IOCTL_VERSION. 66 DRM_IOCTL_VERSION.
67 67
68 The driver description is a purely informative 68 The driver description is a purely informative string passed to
69 userspace through the DRM_IOCTL_VERSION ioctl 69 userspace through the DRM_IOCTL_VERSION ioctl and otherwise unused by
70 the kernel. 70 the kernel.
71 71
>> 72 The driver date, formatted as YYYYMMDD, is meant to identify the date of
>> 73 the latest modification to the driver. However, as most drivers fail to
>> 74 update it, its value is mostly useless. The DRM core prints it to the
>> 75 kernel log at initialization time and passes it to userspace through the
>> 76 DRM_IOCTL_VERSION ioctl.
>> 77
72 Module Initialization 78 Module Initialization
73 --------------------- 79 ---------------------
74 80
75 .. kernel-doc:: include/drm/drm_module.h 81 .. kernel-doc:: include/drm/drm_module.h
76 :doc: overview 82 :doc: overview
77 83
78 Managing Ownership of the Framebuffer Aperture 84 Managing Ownership of the Framebuffer Aperture
79 ---------------------------------------------- 85 ----------------------------------------------
80 86
81 .. kernel-doc:: drivers/gpu/drm/drm_aperture.c 87 .. kernel-doc:: drivers/gpu/drm/drm_aperture.c
82 :doc: overview 88 :doc: overview
83 89
84 .. kernel-doc:: include/drm/drm_aperture.h 90 .. kernel-doc:: include/drm/drm_aperture.h
85 :internal: 91 :internal:
86 92
87 .. kernel-doc:: drivers/gpu/drm/drm_aperture.c 93 .. kernel-doc:: drivers/gpu/drm/drm_aperture.c
88 :export: 94 :export:
89 95
90 Device Instance and Driver Handling 96 Device Instance and Driver Handling
91 ----------------------------------- 97 -----------------------------------
92 98
93 .. kernel-doc:: drivers/gpu/drm/drm_drv.c 99 .. kernel-doc:: drivers/gpu/drm/drm_drv.c
94 :doc: driver instance overview 100 :doc: driver instance overview
95 101
96 .. kernel-doc:: include/drm/drm_device.h 102 .. kernel-doc:: include/drm/drm_device.h
97 :internal: 103 :internal:
98 104
99 .. kernel-doc:: include/drm/drm_drv.h 105 .. kernel-doc:: include/drm/drm_drv.h
100 :internal: 106 :internal:
101 107
102 .. kernel-doc:: drivers/gpu/drm/drm_drv.c 108 .. kernel-doc:: drivers/gpu/drm/drm_drv.c
103 :export: 109 :export:
104 110
105 Driver Load 111 Driver Load
106 ----------- 112 -----------
107 113
108 Component Helper Usage 114 Component Helper Usage
109 ~~~~~~~~~~~~~~~~~~~~~~ 115 ~~~~~~~~~~~~~~~~~~~~~~
110 116
111 .. kernel-doc:: drivers/gpu/drm/drm_drv.c 117 .. kernel-doc:: drivers/gpu/drm/drm_drv.c
112 :doc: component helper usage recommendation 118 :doc: component helper usage recommendations
113 119
114 Memory Manager Initialization 120 Memory Manager Initialization
115 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 121 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
116 122
117 Every DRM driver requires a memory manager whi 123 Every DRM driver requires a memory manager which must be initialized at
118 load time. DRM currently contains two memory m 124 load time. DRM currently contains two memory managers, the Translation
119 Table Manager (TTM) and the Graphics Execution 125 Table Manager (TTM) and the Graphics Execution Manager (GEM). This
120 document describes the use of the GEM memory m 126 document describes the use of the GEM memory manager only. See ? for
121 details. 127 details.
122 128
123 Miscellaneous Device Configuration 129 Miscellaneous Device Configuration
124 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 130 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
125 131
126 Another task that may be necessary for PCI dev 132 Another task that may be necessary for PCI devices during configuration
127 is mapping the video BIOS. On many devices, th 133 is mapping the video BIOS. On many devices, the VBIOS describes device
128 configuration, LCD panel timings (if any), and 134 configuration, LCD panel timings (if any), and contains flags indicating
129 device state. Mapping the BIOS can be done usi 135 device state. Mapping the BIOS can be done using the pci_map_rom()
130 call, a convenience function that takes care o 136 call, a convenience function that takes care of mapping the actual ROM,
131 whether it has been shadowed into memory (typi 137 whether it has been shadowed into memory (typically at address 0xc0000)
132 or exists on the PCI device in the ROM BAR. No 138 or exists on the PCI device in the ROM BAR. Note that after the ROM has
133 been mapped and any necessary information has 139 been mapped and any necessary information has been extracted, it should
134 be unmapped; on many devices, the ROM address 140 be unmapped; on many devices, the ROM address decoder is shared with
135 other BARs, so leaving it mapped could cause u 141 other BARs, so leaving it mapped could cause undesired behaviour like
136 hangs or memory corruption. 142 hangs or memory corruption.
137 143
138 Managed Resources 144 Managed Resources
139 ----------------- 145 -----------------
140 146
141 .. kernel-doc:: drivers/gpu/drm/drm_managed.c 147 .. kernel-doc:: drivers/gpu/drm/drm_managed.c
142 :doc: managed resources 148 :doc: managed resources
143 149
144 .. kernel-doc:: drivers/gpu/drm/drm_managed.c 150 .. kernel-doc:: drivers/gpu/drm/drm_managed.c
145 :export: 151 :export:
146 152
147 .. kernel-doc:: include/drm/drm_managed.h 153 .. kernel-doc:: include/drm/drm_managed.h
148 :internal: 154 :internal:
>> 155
>> 156 Bus-specific Device Registration and PCI Support
>> 157 ------------------------------------------------
>> 158
>> 159 A number of functions are provided to help with device registration. The
>> 160 functions deal with PCI and platform devices respectively and are only
>> 161 provided for historical reasons. These are all deprecated and shouldn't
>> 162 be used in new drivers. Besides that there's a few helpers for pci
>> 163 drivers.
>> 164
>> 165 .. kernel-doc:: drivers/gpu/drm/drm_pci.c
>> 166 :export:
149 167
150 Open/Close, File Operations and IOCTLs 168 Open/Close, File Operations and IOCTLs
151 ====================================== 169 ======================================
152 170
153 .. _drm_driver_fops: 171 .. _drm_driver_fops:
154 172
155 File Operations 173 File Operations
156 --------------- 174 ---------------
157 175
158 .. kernel-doc:: drivers/gpu/drm/drm_file.c 176 .. kernel-doc:: drivers/gpu/drm/drm_file.c
159 :doc: file operations 177 :doc: file operations
160 178
161 .. kernel-doc:: include/drm/drm_file.h 179 .. kernel-doc:: include/drm/drm_file.h
162 :internal: 180 :internal:
163 181
164 .. kernel-doc:: drivers/gpu/drm/drm_file.c 182 .. kernel-doc:: drivers/gpu/drm/drm_file.c
165 :export: 183 :export:
166 184
167 Misc Utilities 185 Misc Utilities
168 ============== 186 ==============
169 187
170 Printer 188 Printer
171 ------- 189 -------
172 190
173 .. kernel-doc:: include/drm/drm_print.h 191 .. kernel-doc:: include/drm/drm_print.h
174 :doc: print 192 :doc: print
175 193
176 .. kernel-doc:: include/drm/drm_print.h 194 .. kernel-doc:: include/drm/drm_print.h
177 :internal: 195 :internal:
178 196
179 .. kernel-doc:: drivers/gpu/drm/drm_print.c 197 .. kernel-doc:: drivers/gpu/drm/drm_print.c
180 :export: 198 :export:
181 199
182 Utilities 200 Utilities
183 --------- 201 ---------
184 202
185 .. kernel-doc:: include/drm/drm_util.h 203 .. kernel-doc:: include/drm/drm_util.h
186 :doc: drm utils 204 :doc: drm utils
187 205
188 .. kernel-doc:: include/drm/drm_util.h 206 .. kernel-doc:: include/drm/drm_util.h
189 :internal: 207 :internal:
190 208
191 209
192 Unit testing 210 Unit testing
193 ============ 211 ============
194 212
195 KUnit 213 KUnit
196 ----- 214 -----
197 215
198 KUnit (Kernel unit testing framework) provides 216 KUnit (Kernel unit testing framework) provides a common framework for unit tests
199 within the Linux kernel. 217 within the Linux kernel.
200 218
201 This section covers the specifics for the DRM 219 This section covers the specifics for the DRM subsystem. For general information
202 about KUnit, please refer to Documentation/dev 220 about KUnit, please refer to Documentation/dev-tools/kunit/start.rst.
203 221
204 How to run the tests? 222 How to run the tests?
205 ~~~~~~~~~~~~~~~~~~~~~ 223 ~~~~~~~~~~~~~~~~~~~~~
206 224
207 In order to facilitate running the test suite, 225 In order to facilitate running the test suite, a configuration file is present
208 in ``drivers/gpu/drm/tests/.kunitconfig``. It 226 in ``drivers/gpu/drm/tests/.kunitconfig``. It can be used by ``kunit.py`` as
209 follows: 227 follows:
210 228
211 .. code-block:: bash 229 .. code-block:: bash
212 230
213 $ ./tools/testing/kunit/kunit.py run - 231 $ ./tools/testing/kunit/kunit.py run --kunitconfig=drivers/gpu/drm/tests \
214 --kconfig_add CONFIG_VIRTIO_UM 232 --kconfig_add CONFIG_VIRTIO_UML=y \
215 --kconfig_add CONFIG_UML_PCI_O 233 --kconfig_add CONFIG_UML_PCI_OVER_VIRTIO=y
216 234
217 .. note:: 235 .. note::
218 The configuration included in ``.kunit 236 The configuration included in ``.kunitconfig`` should be as generic as
219 possible. 237 possible.
220 ``CONFIG_VIRTIO_UML`` and ``CONFIG_UML 238 ``CONFIG_VIRTIO_UML`` and ``CONFIG_UML_PCI_OVER_VIRTIO`` are not
221 included in it because they are only r 239 included in it because they are only required for User Mode Linux.
222 240
223 241
224 Legacy Support Code 242 Legacy Support Code
225 =================== 243 ===================
226 244
227 The section very briefly covers some of the ol 245 The section very briefly covers some of the old legacy support code
228 which is only used by old DRM drivers which ha 246 which is only used by old DRM drivers which have done a so-called
229 shadow-attach to the underlying device instead 247 shadow-attach to the underlying device instead of registering as a real
230 driver. This also includes some of the old gen 248 driver. This also includes some of the old generic buffer management and
231 command submission code. Do not use any of thi 249 command submission code. Do not use any of this in new and modern
232 drivers. 250 drivers.
233 251
234 Legacy Suspend/Resume 252 Legacy Suspend/Resume
235 --------------------- 253 ---------------------
236 254
237 The DRM core provides some suspend/resume code 255 The DRM core provides some suspend/resume code, but drivers wanting full
238 suspend/resume support should provide save() a 256 suspend/resume support should provide save() and restore() functions.
239 These are called at suspend, hibernate, or res 257 These are called at suspend, hibernate, or resume time, and should
240 perform any state save or restore required by 258 perform any state save or restore required by your device across suspend
241 or hibernate states. 259 or hibernate states.
242 260
243 int (\*suspend) (struct drm_device \*, pm_mess 261 int (\*suspend) (struct drm_device \*, pm_message_t state); int
244 (\*resume) (struct drm_device \*); 262 (\*resume) (struct drm_device \*);
245 Those are legacy suspend and resume methods wh 263 Those are legacy suspend and resume methods which *only* work with the
246 legacy shadow-attach driver registration funct 264 legacy shadow-attach driver registration functions. New driver should
247 use the power management interface provided by 265 use the power management interface provided by their bus type (usually
248 through the :c:type:`struct device_driver <dev 266 through the :c:type:`struct device_driver <device_driver>`
249 dev_pm_ops) and set these methods to NULL. 267 dev_pm_ops) and set these methods to NULL.
250 268
251 Legacy DMA Services 269 Legacy DMA Services
252 ------------------- 270 -------------------
253 271
254 This should cover how DMA mapping etc. is supp 272 This should cover how DMA mapping etc. is supported by the core. These
255 functions are deprecated and should not be use 273 functions are deprecated and should not be used.
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