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 Driver Features
>> 43 ~~~~~~~~~~~~~~~
>> 44
>> 45 Drivers inform the DRM core about their requirements and supported
>> 46 features by setting appropriate flags in the driver_features field.
>> 47 Since those flags influence the DRM core behaviour since registration
>> 48 time, most of them must be set to registering the :c:type:`struct
>> 49 drm_driver <drm_driver>` instance.
>> 50
>> 51 u32 driver_features;
>> 52
>> 53 DRIVER_USE_AGP
>> 54 Driver uses AGP interface, the DRM core will manage AGP resources.
>> 55
>> 56 DRIVER_LEGACY
>> 57 Denote a legacy driver using shadow attach. Don't use.
>> 58
>> 59 DRIVER_KMS_LEGACY_CONTEXT
>> 60 Used only by nouveau for backwards compatibility with existing userspace.
>> 61 Don't use.
>> 62
>> 63 DRIVER_PCI_DMA
>> 64 Driver is capable of PCI DMA, mapping of PCI DMA buffers to
>> 65 userspace will be enabled. Deprecated.
>> 66
>> 67 DRIVER_SG
>> 68 Driver can perform scatter/gather DMA, allocation and mapping of
>> 69 scatter/gather buffers will be enabled. Deprecated.
>> 70
>> 71 DRIVER_HAVE_DMA
>> 72 Driver supports DMA, the userspace DMA API will be supported.
>> 73 Deprecated.
>> 74
>> 75 DRIVER_HAVE_IRQ; DRIVER_IRQ_SHARED
>> 76 DRIVER_HAVE_IRQ indicates whether the driver has an IRQ handler
>> 77 managed by the DRM Core. The core will support simple IRQ handler
>> 78 installation when the flag is set. The installation process is
>> 79 described in ?.
>> 80
>> 81 DRIVER_IRQ_SHARED indicates whether the device & handler support
>> 82 shared IRQs (note that this is required of PCI drivers).
>> 83
>> 84 DRIVER_GEM
>> 85 Driver use the GEM memory manager.
>> 86
>> 87 DRIVER_MODESET
>> 88 Driver supports mode setting interfaces (KMS).
>> 89
>> 90 DRIVER_PRIME
>> 91 Driver implements DRM PRIME buffer sharing.
>> 92
>> 93 DRIVER_RENDER
>> 94 Driver supports dedicated render nodes.
>> 95
>> 96 DRIVER_ATOMIC
>> 97 Driver supports atomic properties. In this case the driver must
>> 98 implement appropriate obj->atomic_get_property() vfuncs for any
>> 99 modeset objects with driver specific properties.
>> 100
>> 101 DRIVER_SYNCOBJ
>> 102 Driver support drm sync objects.
>> 103
42 Major, Minor and Patchlevel 104 Major, Minor and Patchlevel
43 ~~~~~~~~~~~~~~~~~~~~~~~~~~~ 105 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
44 106
45 int major; int minor; int patchlevel; 107 int major; int minor; int patchlevel;
46 The DRM core identifies driver versions by a m 108 The DRM core identifies driver versions by a major, minor and patch
47 level triplet. The information is printed to t 109 level triplet. The information is printed to the kernel log at
48 initialization time and passed to userspace th 110 initialization time and passed to userspace through the
49 DRM_IOCTL_VERSION ioctl. 111 DRM_IOCTL_VERSION ioctl.
50 112
51 The major and minor numbers are also used to v 113 The major and minor numbers are also used to verify the requested driver
52 API version passed to DRM_IOCTL_SET_VERSION. W 114 API version passed to DRM_IOCTL_SET_VERSION. When the driver API
53 changes between minor versions, applications c 115 changes between minor versions, applications can call
54 DRM_IOCTL_SET_VERSION to select a specific ver 116 DRM_IOCTL_SET_VERSION to select a specific version of the API. If the
55 requested major isn't equal to the driver majo 117 requested major isn't equal to the driver major, or the requested minor
56 is larger than the driver minor, the DRM_IOCTL 118 is larger than the driver minor, the DRM_IOCTL_SET_VERSION call will
57 return an error. Otherwise the driver's set_ve 119 return an error. Otherwise the driver's set_version() method will be
58 called with the requested version. 120 called with the requested version.
59 121
60 Name and Description !! 122 Name, Description and Date
61 ~~~~~~~~~~~~~~~~~~~~ !! 123 ~~~~~~~~~~~~~~~~~~~~~~~~~~
62 124
63 char \*name; char \*desc; char \*date; 125 char \*name; char \*desc; char \*date;
64 The driver name is printed to the kernel log a 126 The driver name is printed to the kernel log at initialization time,
65 used for IRQ registration and passed to usersp 127 used for IRQ registration and passed to userspace through
66 DRM_IOCTL_VERSION. 128 DRM_IOCTL_VERSION.
67 129
68 The driver description is a purely informative 130 The driver description is a purely informative string passed to
69 userspace through the DRM_IOCTL_VERSION ioctl 131 userspace through the DRM_IOCTL_VERSION ioctl and otherwise unused by
70 the kernel. 132 the kernel.
71 133
72 Module Initialization !! 134 The driver date, formatted as YYYYMMDD, is meant to identify the date of
73 --------------------- !! 135 the latest modification to the driver. However, as most drivers fail to
74 !! 136 update it, its value is mostly useless. The DRM core prints it to the
75 .. kernel-doc:: include/drm/drm_module.h !! 137 kernel log at initialization time and passes it to userspace through the
76 :doc: overview !! 138 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: <<
89 139
90 Device Instance and Driver Handling 140 Device Instance and Driver Handling
91 ----------------------------------- 141 -----------------------------------
92 142
93 .. kernel-doc:: drivers/gpu/drm/drm_drv.c 143 .. kernel-doc:: drivers/gpu/drm/drm_drv.c
94 :doc: driver instance overview 144 :doc: driver instance overview
95 145
96 .. kernel-doc:: include/drm/drm_device.h <<
97 :internal: <<
98 <<
99 .. kernel-doc:: include/drm/drm_drv.h 146 .. kernel-doc:: include/drm/drm_drv.h
100 :internal: 147 :internal:
101 148
102 .. kernel-doc:: drivers/gpu/drm/drm_drv.c 149 .. kernel-doc:: drivers/gpu/drm/drm_drv.c
103 :export: 150 :export:
104 151
105 Driver Load 152 Driver Load
106 ----------- 153 -----------
107 154
108 Component Helper Usage <<
109 ~~~~~~~~~~~~~~~~~~~~~~ <<
110 155
111 .. kernel-doc:: drivers/gpu/drm/drm_drv.c !! 156 IRQ Helper Library
112 :doc: component helper usage recommendation !! 157 ~~~~~~~~~~~~~~~~~~
>> 158
>> 159 .. kernel-doc:: drivers/gpu/drm/drm_irq.c
>> 160 :doc: irq helpers
>> 161
>> 162 .. kernel-doc:: drivers/gpu/drm/drm_irq.c
>> 163 :export:
113 164
114 Memory Manager Initialization 165 Memory Manager Initialization
115 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 166 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
116 167
117 Every DRM driver requires a memory manager whi 168 Every DRM driver requires a memory manager which must be initialized at
118 load time. DRM currently contains two memory m 169 load time. DRM currently contains two memory managers, the Translation
119 Table Manager (TTM) and the Graphics Execution 170 Table Manager (TTM) and the Graphics Execution Manager (GEM). This
120 document describes the use of the GEM memory m 171 document describes the use of the GEM memory manager only. See ? for
121 details. 172 details.
122 173
123 Miscellaneous Device Configuration 174 Miscellaneous Device Configuration
124 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 175 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
125 176
126 Another task that may be necessary for PCI dev 177 Another task that may be necessary for PCI devices during configuration
127 is mapping the video BIOS. On many devices, th 178 is mapping the video BIOS. On many devices, the VBIOS describes device
128 configuration, LCD panel timings (if any), and 179 configuration, LCD panel timings (if any), and contains flags indicating
129 device state. Mapping the BIOS can be done usi 180 device state. Mapping the BIOS can be done using the pci_map_rom()
130 call, a convenience function that takes care o 181 call, a convenience function that takes care of mapping the actual ROM,
131 whether it has been shadowed into memory (typi 182 whether it has been shadowed into memory (typically at address 0xc0000)
132 or exists on the PCI device in the ROM BAR. No 183 or exists on the PCI device in the ROM BAR. Note that after the ROM has
133 been mapped and any necessary information has 184 been mapped and any necessary information has been extracted, it should
134 be unmapped; on many devices, the ROM address 185 be unmapped; on many devices, the ROM address decoder is shared with
135 other BARs, so leaving it mapped could cause u 186 other BARs, so leaving it mapped could cause undesired behaviour like
136 hangs or memory corruption. 187 hangs or memory corruption.
137 188
138 Managed Resources !! 189 Bus-specific Device Registration and PCI Support
139 ----------------- !! 190 ------------------------------------------------
140 191
141 .. kernel-doc:: drivers/gpu/drm/drm_managed.c !! 192 A number of functions are provided to help with device registration. The
142 :doc: managed resources !! 193 functions deal with PCI and platform devices respectively and are only
>> 194 provided for historical reasons. These are all deprecated and shouldn't
>> 195 be used in new drivers. Besides that there's a few helpers for pci
>> 196 drivers.
143 197
144 .. kernel-doc:: drivers/gpu/drm/drm_managed.c !! 198 .. kernel-doc:: drivers/gpu/drm/drm_pci.c
145 :export: 199 :export:
146 200
147 .. kernel-doc:: include/drm/drm_managed.h <<
148 :internal: <<
149 <<
150 Open/Close, File Operations and IOCTLs 201 Open/Close, File Operations and IOCTLs
151 ====================================== 202 ======================================
152 203
153 .. _drm_driver_fops: 204 .. _drm_driver_fops:
154 205
155 File Operations 206 File Operations
156 --------------- 207 ---------------
157 208
158 .. kernel-doc:: drivers/gpu/drm/drm_file.c 209 .. kernel-doc:: drivers/gpu/drm/drm_file.c
159 :doc: file operations 210 :doc: file operations
160 211
161 .. kernel-doc:: include/drm/drm_file.h 212 .. kernel-doc:: include/drm/drm_file.h
162 :internal: 213 :internal:
163 214
164 .. kernel-doc:: drivers/gpu/drm/drm_file.c 215 .. kernel-doc:: drivers/gpu/drm/drm_file.c
165 :export: 216 :export:
166 217
167 Misc Utilities 218 Misc Utilities
168 ============== 219 ==============
169 220
170 Printer 221 Printer
171 ------- 222 -------
172 223
173 .. kernel-doc:: include/drm/drm_print.h 224 .. kernel-doc:: include/drm/drm_print.h
174 :doc: print 225 :doc: print
175 226
176 .. kernel-doc:: include/drm/drm_print.h 227 .. kernel-doc:: include/drm/drm_print.h
177 :internal: 228 :internal:
178 229
179 .. kernel-doc:: drivers/gpu/drm/drm_print.c 230 .. kernel-doc:: drivers/gpu/drm/drm_print.c
180 :export: 231 :export:
181 <<
182 Utilities <<
183 --------- <<
184 <<
185 .. kernel-doc:: include/drm/drm_util.h <<
186 :doc: drm utils <<
187 <<
188 .. kernel-doc:: include/drm/drm_util.h <<
189 :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 <<
222 232
223 233
224 Legacy Support Code 234 Legacy Support Code
225 =================== 235 ===================
226 236
227 The section very briefly covers some of the ol 237 The section very briefly covers some of the old legacy support code
228 which is only used by old DRM drivers which ha 238 which is only used by old DRM drivers which have done a so-called
229 shadow-attach to the underlying device instead 239 shadow-attach to the underlying device instead of registering as a real
230 driver. This also includes some of the old gen 240 driver. This also includes some of the old generic buffer management and
231 command submission code. Do not use any of thi 241 command submission code. Do not use any of this in new and modern
232 drivers. 242 drivers.
233 243
234 Legacy Suspend/Resume 244 Legacy Suspend/Resume
235 --------------------- 245 ---------------------
236 246
237 The DRM core provides some suspend/resume code 247 The DRM core provides some suspend/resume code, but drivers wanting full
238 suspend/resume support should provide save() a 248 suspend/resume support should provide save() and restore() functions.
239 These are called at suspend, hibernate, or res 249 These are called at suspend, hibernate, or resume time, and should
240 perform any state save or restore required by 250 perform any state save or restore required by your device across suspend
241 or hibernate states. 251 or hibernate states.
242 252
243 int (\*suspend) (struct drm_device \*, pm_mess 253 int (\*suspend) (struct drm_device \*, pm_message_t state); int
244 (\*resume) (struct drm_device \*); 254 (\*resume) (struct drm_device \*);
245 Those are legacy suspend and resume methods wh 255 Those are legacy suspend and resume methods which *only* work with the
246 legacy shadow-attach driver registration funct 256 legacy shadow-attach driver registration functions. New driver should
247 use the power management interface provided by 257 use the power management interface provided by their bus type (usually
248 through the :c:type:`struct device_driver <dev 258 through the :c:type:`struct device_driver <device_driver>`
249 dev_pm_ops) and set these methods to NULL. 259 dev_pm_ops) and set these methods to NULL.
250 260
251 Legacy DMA Services 261 Legacy DMA Services
252 ------------------- 262 -------------------
253 263
254 This should cover how DMA mapping etc. is supp 264 This should cover how DMA mapping etc. is supported by the core. These
255 functions are deprecated and should not be use 265 functions are deprecated and should not be used.
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