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 :c:func:`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 :c:func:`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 Module Initialization !! 72 The driver date, formatted as YYYYMMDD, is meant to identify the date of
73 --------------------- !! 73 the latest modification to the driver. However, as most drivers fail to
74 !! 74 update it, its value is mostly useless. The DRM core prints it to the
75 .. kernel-doc:: include/drm/drm_module.h !! 75 kernel log at initialization time and passes it to userspace through the
76 :doc: overview !! 76 DRM_IOCTL_VERSION ioctl.
77 <<
78 Managing Ownership of the Framebuffer Aperture <<
79 ---------------------------------------------- <<
80 <<
81 .. kernel-doc:: drivers/gpu/drm/drm_aperture.c <<
82 :doc: overview <<
83 <<
84 .. kernel-doc:: include/drm/drm_aperture.h <<
85 :internal: <<
86 <<
87 .. kernel-doc:: drivers/gpu/drm/drm_aperture.c <<
88 :export: <<
89 77
90 Device Instance and Driver Handling 78 Device Instance and Driver Handling
91 ----------------------------------- 79 -----------------------------------
92 80
93 .. kernel-doc:: drivers/gpu/drm/drm_drv.c 81 .. kernel-doc:: drivers/gpu/drm/drm_drv.c
94 :doc: driver instance overview 82 :doc: driver instance overview
95 83
96 .. kernel-doc:: include/drm/drm_device.h 84 .. kernel-doc:: include/drm/drm_device.h
97 :internal: 85 :internal:
98 86
99 .. kernel-doc:: include/drm/drm_drv.h 87 .. kernel-doc:: include/drm/drm_drv.h
100 :internal: 88 :internal:
101 89
102 .. kernel-doc:: drivers/gpu/drm/drm_drv.c 90 .. kernel-doc:: drivers/gpu/drm/drm_drv.c
103 :export: 91 :export:
104 92
105 Driver Load 93 Driver Load
106 ----------- 94 -----------
107 95
108 Component Helper Usage 96 Component Helper Usage
109 ~~~~~~~~~~~~~~~~~~~~~~ 97 ~~~~~~~~~~~~~~~~~~~~~~
110 98
111 .. kernel-doc:: drivers/gpu/drm/drm_drv.c 99 .. kernel-doc:: drivers/gpu/drm/drm_drv.c
112 :doc: component helper usage recommendation 100 :doc: component helper usage recommendations
113 101
>> 102 IRQ Helper Library
>> 103 ~~~~~~~~~~~~~~~~~~
>> 104
>> 105 .. kernel-doc:: drivers/gpu/drm/drm_irq.c
>> 106 :doc: irq helpers
>> 107
>> 108 .. kernel-doc:: drivers/gpu/drm/drm_irq.c
>> 109 :export:
>> 110
114 Memory Manager Initialization 111 Memory Manager Initialization
115 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 112 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
116 113
117 Every DRM driver requires a memory manager whi 114 Every DRM driver requires a memory manager which must be initialized at
118 load time. DRM currently contains two memory m 115 load time. DRM currently contains two memory managers, the Translation
119 Table Manager (TTM) and the Graphics Execution 116 Table Manager (TTM) and the Graphics Execution Manager (GEM). This
120 document describes the use of the GEM memory m 117 document describes the use of the GEM memory manager only. See ? for
121 details. 118 details.
122 119
123 Miscellaneous Device Configuration 120 Miscellaneous Device Configuration
124 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 121 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
125 122
126 Another task that may be necessary for PCI dev 123 Another task that may be necessary for PCI devices during configuration
127 is mapping the video BIOS. On many devices, th 124 is mapping the video BIOS. On many devices, the VBIOS describes device
128 configuration, LCD panel timings (if any), and 125 configuration, LCD panel timings (if any), and contains flags indicating
129 device state. Mapping the BIOS can be done usi 126 device state. Mapping the BIOS can be done using the pci_map_rom()
130 call, a convenience function that takes care o 127 call, a convenience function that takes care of mapping the actual ROM,
131 whether it has been shadowed into memory (typi 128 whether it has been shadowed into memory (typically at address 0xc0000)
132 or exists on the PCI device in the ROM BAR. No 129 or exists on the PCI device in the ROM BAR. Note that after the ROM has
133 been mapped and any necessary information has 130 been mapped and any necessary information has been extracted, it should
134 be unmapped; on many devices, the ROM address 131 be unmapped; on many devices, the ROM address decoder is shared with
135 other BARs, so leaving it mapped could cause u 132 other BARs, so leaving it mapped could cause undesired behaviour like
136 hangs or memory corruption. 133 hangs or memory corruption.
137 134
138 Managed Resources !! 135 Bus-specific Device Registration and PCI Support
139 ----------------- !! 136 ------------------------------------------------
140 137
141 .. kernel-doc:: drivers/gpu/drm/drm_managed.c !! 138 A number of functions are provided to help with device registration. The
142 :doc: managed resources !! 139 functions deal with PCI and platform devices respectively and are only
>> 140 provided for historical reasons. These are all deprecated and shouldn't
>> 141 be used in new drivers. Besides that there's a few helpers for pci
>> 142 drivers.
143 143
144 .. kernel-doc:: drivers/gpu/drm/drm_managed.c !! 144 .. kernel-doc:: drivers/gpu/drm/drm_pci.c
145 :export: 145 :export:
146 146
147 .. kernel-doc:: include/drm/drm_managed.h <<
148 :internal: <<
149 <<
150 Open/Close, File Operations and IOCTLs 147 Open/Close, File Operations and IOCTLs
151 ====================================== 148 ======================================
152 149
153 .. _drm_driver_fops: 150 .. _drm_driver_fops:
154 151
155 File Operations 152 File Operations
156 --------------- 153 ---------------
157 154
158 .. kernel-doc:: drivers/gpu/drm/drm_file.c 155 .. kernel-doc:: drivers/gpu/drm/drm_file.c
159 :doc: file operations 156 :doc: file operations
160 157
161 .. kernel-doc:: include/drm/drm_file.h 158 .. kernel-doc:: include/drm/drm_file.h
162 :internal: 159 :internal:
163 160
164 .. kernel-doc:: drivers/gpu/drm/drm_file.c 161 .. kernel-doc:: drivers/gpu/drm/drm_file.c
165 :export: 162 :export:
166 163
167 Misc Utilities 164 Misc Utilities
168 ============== 165 ==============
169 166
170 Printer 167 Printer
171 ------- 168 -------
172 169
173 .. kernel-doc:: include/drm/drm_print.h 170 .. kernel-doc:: include/drm/drm_print.h
174 :doc: print 171 :doc: print
175 172
176 .. kernel-doc:: include/drm/drm_print.h 173 .. kernel-doc:: include/drm/drm_print.h
177 :internal: 174 :internal:
178 175
179 .. kernel-doc:: drivers/gpu/drm/drm_print.c 176 .. kernel-doc:: drivers/gpu/drm/drm_print.c
180 :export: 177 :export:
181 178
182 Utilities 179 Utilities
183 --------- 180 ---------
184 181
185 .. kernel-doc:: include/drm/drm_util.h 182 .. kernel-doc:: include/drm/drm_util.h
186 :doc: drm utils 183 :doc: drm utils
187 184
188 .. kernel-doc:: include/drm/drm_util.h 185 .. kernel-doc:: include/drm/drm_util.h
189 :internal: 186 :internal:
190 <<
191 <<
192 Unit testing <<
193 ============ <<
194 <<
195 KUnit <<
196 ----- <<
197 <<
198 KUnit (Kernel unit testing framework) provides <<
199 within the Linux kernel. <<
200 <<
201 This section covers the specifics for the DRM <<
202 about KUnit, please refer to Documentation/dev <<
203 <<
204 How to run the tests? <<
205 ~~~~~~~~~~~~~~~~~~~~~ <<
206 <<
207 In order to facilitate running the test suite, <<
208 in ``drivers/gpu/drm/tests/.kunitconfig``. It <<
209 follows: <<
210 <<
211 .. code-block:: bash <<
212 <<
213 $ ./tools/testing/kunit/kunit.py run - <<
214 --kconfig_add CONFIG_VIRTIO_UM <<
215 --kconfig_add CONFIG_UML_PCI_O <<
216 <<
217 .. note:: <<
218 The configuration included in ``.kunit <<
219 possible. <<
220 ``CONFIG_VIRTIO_UML`` and ``CONFIG_UML <<
221 included in it because they are only r <<
222 187
223 188
224 Legacy Support Code 189 Legacy Support Code
225 =================== 190 ===================
226 191
227 The section very briefly covers some of the ol 192 The section very briefly covers some of the old legacy support code
228 which is only used by old DRM drivers which ha 193 which is only used by old DRM drivers which have done a so-called
229 shadow-attach to the underlying device instead 194 shadow-attach to the underlying device instead of registering as a real
230 driver. This also includes some of the old gen 195 driver. This also includes some of the old generic buffer management and
231 command submission code. Do not use any of thi 196 command submission code. Do not use any of this in new and modern
232 drivers. 197 drivers.
233 198
234 Legacy Suspend/Resume 199 Legacy Suspend/Resume
235 --------------------- 200 ---------------------
236 201
237 The DRM core provides some suspend/resume code 202 The DRM core provides some suspend/resume code, but drivers wanting full
238 suspend/resume support should provide save() a 203 suspend/resume support should provide save() and restore() functions.
239 These are called at suspend, hibernate, or res 204 These are called at suspend, hibernate, or resume time, and should
240 perform any state save or restore required by 205 perform any state save or restore required by your device across suspend
241 or hibernate states. 206 or hibernate states.
242 207
243 int (\*suspend) (struct drm_device \*, pm_mess 208 int (\*suspend) (struct drm_device \*, pm_message_t state); int
244 (\*resume) (struct drm_device \*); 209 (\*resume) (struct drm_device \*);
245 Those are legacy suspend and resume methods wh 210 Those are legacy suspend and resume methods which *only* work with the
246 legacy shadow-attach driver registration funct 211 legacy shadow-attach driver registration functions. New driver should
247 use the power management interface provided by 212 use the power management interface provided by their bus type (usually
248 through the :c:type:`struct device_driver <dev 213 through the :c:type:`struct device_driver <device_driver>`
249 dev_pm_ops) and set these methods to NULL. 214 dev_pm_ops) and set these methods to NULL.
250 215
251 Legacy DMA Services 216 Legacy DMA Services
252 ------------------- 217 -------------------
253 218
254 This should cover how DMA mapping etc. is supp 219 This should cover how DMA mapping etc. is supported by the core. These
255 functions are deprecated and should not be use 220 functions are deprecated and should not be used.
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