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
42 Major, Minor and Patchlevel 101 Major, Minor and Patchlevel
43 ~~~~~~~~~~~~~~~~~~~~~~~~~~~ 102 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
44 103
45 int major; int minor; int patchlevel; 104 int major; int minor; int patchlevel;
46 The DRM core identifies driver versions by a m 105 The DRM core identifies driver versions by a major, minor and patch
47 level triplet. The information is printed to t 106 level triplet. The information is printed to the kernel log at
48 initialization time and passed to userspace th 107 initialization time and passed to userspace through the
49 DRM_IOCTL_VERSION ioctl. 108 DRM_IOCTL_VERSION ioctl.
50 109
51 The major and minor numbers are also used to v 110 The major and minor numbers are also used to verify the requested driver
52 API version passed to DRM_IOCTL_SET_VERSION. W 111 API version passed to DRM_IOCTL_SET_VERSION. When the driver API
53 changes between minor versions, applications c 112 changes between minor versions, applications can call
54 DRM_IOCTL_SET_VERSION to select a specific ver 113 DRM_IOCTL_SET_VERSION to select a specific version of the API. If the
55 requested major isn't equal to the driver majo 114 requested major isn't equal to the driver major, or the requested minor
56 is larger than the driver minor, the DRM_IOCTL 115 is larger than the driver minor, the DRM_IOCTL_SET_VERSION call will
57 return an error. Otherwise the driver's set_ve 116 return an error. Otherwise the driver's set_version() method will be
58 called with the requested version. 117 called with the requested version.
59 118
60 Name and Description !! 119 Name, Description and Date
61 ~~~~~~~~~~~~~~~~~~~~ !! 120 ~~~~~~~~~~~~~~~~~~~~~~~~~~
62 121
63 char \*name; char \*desc; char \*date; 122 char \*name; char \*desc; char \*date;
64 The driver name is printed to the kernel log a 123 The driver name is printed to the kernel log at initialization time,
65 used for IRQ registration and passed to usersp 124 used for IRQ registration and passed to userspace through
66 DRM_IOCTL_VERSION. 125 DRM_IOCTL_VERSION.
67 126
68 The driver description is a purely informative 127 The driver description is a purely informative string passed to
69 userspace through the DRM_IOCTL_VERSION ioctl 128 userspace through the DRM_IOCTL_VERSION ioctl and otherwise unused by
70 the kernel. 129 the kernel.
71 130
72 Module Initialization !! 131 The driver date, formatted as YYYYMMDD, is meant to identify the date of
73 --------------------- !! 132 the latest modification to the driver. However, as most drivers fail to
74 !! 133 update it, its value is mostly useless. The DRM core prints it to the
75 .. kernel-doc:: include/drm/drm_module.h !! 134 kernel log at initialization time and passes it to userspace through the
76 :doc: overview !! 135 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: <<
89 136
90 Device Instance and Driver Handling 137 Device Instance and Driver Handling
91 ----------------------------------- 138 -----------------------------------
92 139
93 .. kernel-doc:: drivers/gpu/drm/drm_drv.c 140 .. kernel-doc:: drivers/gpu/drm/drm_drv.c
94 :doc: driver instance overview 141 :doc: driver instance overview
95 142
96 .. kernel-doc:: include/drm/drm_device.h <<
97 :internal: <<
98 <<
99 .. kernel-doc:: include/drm/drm_drv.h 143 .. kernel-doc:: include/drm/drm_drv.h
100 :internal: 144 :internal:
101 145
102 .. kernel-doc:: drivers/gpu/drm/drm_drv.c 146 .. kernel-doc:: drivers/gpu/drm/drm_drv.c
103 :export: 147 :export:
104 148
105 Driver Load 149 Driver Load
106 ----------- 150 -----------
107 151
108 Component Helper Usage !! 152 IRQ Registration
109 ~~~~~~~~~~~~~~~~~~~~~~ !! 153 ~~~~~~~~~~~~~~~~
110 154
111 .. kernel-doc:: drivers/gpu/drm/drm_drv.c !! 155 The DRM core tries to facilitate IRQ handler registration and
112 :doc: component helper usage recommendation !! 156 unregistration by providing :c:func:`drm_irq_install()` and
>> 157 :c:func:`drm_irq_uninstall()` functions. Those functions only
>> 158 support a single interrupt per device, devices that use more than one
>> 159 IRQs need to be handled manually.
>> 160
>> 161 Managed IRQ Registration
>> 162 ''''''''''''''''''''''''
>> 163
>> 164 :c:func:`drm_irq_install()` starts by calling the irq_preinstall
>> 165 driver operation. The operation is optional and must make sure that the
>> 166 interrupt will not get fired by clearing all pending interrupt flags or
>> 167 disabling the interrupt.
>> 168
>> 169 The passed-in IRQ will then be requested by a call to
>> 170 :c:func:`request_irq()`. If the DRIVER_IRQ_SHARED driver feature
>> 171 flag is set, a shared (IRQF_SHARED) IRQ handler will be requested.
>> 172
>> 173 The IRQ handler function must be provided as the mandatory irq_handler
>> 174 driver operation. It will get passed directly to
>> 175 :c:func:`request_irq()` and thus has the same prototype as all IRQ
>> 176 handlers. It will get called with a pointer to the DRM device as the
>> 177 second argument.
>> 178
>> 179 Finally the function calls the optional irq_postinstall driver
>> 180 operation. The operation usually enables interrupts (excluding the
>> 181 vblank interrupt, which is enabled separately), but drivers may choose
>> 182 to enable/disable interrupts at a different time.
>> 183
>> 184 :c:func:`drm_irq_uninstall()` is similarly used to uninstall an
>> 185 IRQ handler. It starts by waking up all processes waiting on a vblank
>> 186 interrupt to make sure they don't hang, and then calls the optional
>> 187 irq_uninstall driver operation. The operation must disable all hardware
>> 188 interrupts. Finally the function frees the IRQ by calling
>> 189 :c:func:`free_irq()`.
>> 190
>> 191 Manual IRQ Registration
>> 192 '''''''''''''''''''''''
>> 193
>> 194 Drivers that require multiple interrupt handlers can't use the managed
>> 195 IRQ registration functions. In that case IRQs must be registered and
>> 196 unregistered manually (usually with the :c:func:`request_irq()` and
>> 197 :c:func:`free_irq()` functions, or their :c:func:`devm_request_irq()` and
>> 198 :c:func:`devm_free_irq()` equivalents).
>> 199
>> 200 When manually registering IRQs, drivers must not set the
>> 201 DRIVER_HAVE_IRQ driver feature flag, and must not provide the
>> 202 irq_handler driver operation. They must set the :c:type:`struct
>> 203 drm_device <drm_device>` irq_enabled field to 1 upon
>> 204 registration of the IRQs, and clear it to 0 after unregistering the
>> 205 IRQs.
113 206
114 Memory Manager Initialization 207 Memory Manager Initialization
115 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 208 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
116 209
117 Every DRM driver requires a memory manager whi 210 Every DRM driver requires a memory manager which must be initialized at
118 load time. DRM currently contains two memory m 211 load time. DRM currently contains two memory managers, the Translation
119 Table Manager (TTM) and the Graphics Execution 212 Table Manager (TTM) and the Graphics Execution Manager (GEM). This
120 document describes the use of the GEM memory m 213 document describes the use of the GEM memory manager only. See ? for
121 details. 214 details.
122 215
123 Miscellaneous Device Configuration 216 Miscellaneous Device Configuration
124 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 217 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
125 218
126 Another task that may be necessary for PCI dev 219 Another task that may be necessary for PCI devices during configuration
127 is mapping the video BIOS. On many devices, th 220 is mapping the video BIOS. On many devices, the VBIOS describes device
128 configuration, LCD panel timings (if any), and 221 configuration, LCD panel timings (if any), and contains flags indicating
129 device state. Mapping the BIOS can be done usi 222 device state. Mapping the BIOS can be done using the pci_map_rom()
130 call, a convenience function that takes care o 223 call, a convenience function that takes care of mapping the actual ROM,
131 whether it has been shadowed into memory (typi 224 whether it has been shadowed into memory (typically at address 0xc0000)
132 or exists on the PCI device in the ROM BAR. No 225 or exists on the PCI device in the ROM BAR. Note that after the ROM has
133 been mapped and any necessary information has 226 been mapped and any necessary information has been extracted, it should
134 be unmapped; on many devices, the ROM address 227 be unmapped; on many devices, the ROM address decoder is shared with
135 other BARs, so leaving it mapped could cause u 228 other BARs, so leaving it mapped could cause undesired behaviour like
136 hangs or memory corruption. 229 hangs or memory corruption.
137 230
138 Managed Resources !! 231 Bus-specific Device Registration and PCI Support
139 ----------------- !! 232 ------------------------------------------------
140 233
141 .. kernel-doc:: drivers/gpu/drm/drm_managed.c !! 234 A number of functions are provided to help with device registration. The
142 :doc: managed resources !! 235 functions deal with PCI and platform devices respectively and are only
>> 236 provided for historical reasons. These are all deprecated and shouldn't
>> 237 be used in new drivers. Besides that there's a few helpers for pci
>> 238 drivers.
143 239
144 .. kernel-doc:: drivers/gpu/drm/drm_managed.c !! 240 .. kernel-doc:: drivers/gpu/drm/drm_pci.c
145 :export: 241 :export:
146 242
147 .. kernel-doc:: include/drm/drm_managed.h <<
148 :internal: <<
149 <<
150 Open/Close, File Operations and IOCTLs 243 Open/Close, File Operations and IOCTLs
151 ====================================== 244 ======================================
152 245
153 .. _drm_driver_fops: <<
154 <<
155 File Operations 246 File Operations
156 --------------- 247 ---------------
157 248
158 .. kernel-doc:: drivers/gpu/drm/drm_file.c 249 .. kernel-doc:: drivers/gpu/drm/drm_file.c
159 :doc: file operations 250 :doc: file operations
160 251
161 .. kernel-doc:: include/drm/drm_file.h 252 .. kernel-doc:: include/drm/drm_file.h
162 :internal: 253 :internal:
163 254
164 .. kernel-doc:: drivers/gpu/drm/drm_file.c 255 .. kernel-doc:: drivers/gpu/drm/drm_file.c
165 :export: 256 :export:
166 257
167 Misc Utilities 258 Misc Utilities
168 ============== 259 ==============
169 260
170 Printer 261 Printer
171 ------- 262 -------
172 263
173 .. kernel-doc:: include/drm/drm_print.h 264 .. kernel-doc:: include/drm/drm_print.h
174 :doc: print 265 :doc: print
175 266
176 .. kernel-doc:: include/drm/drm_print.h 267 .. kernel-doc:: include/drm/drm_print.h
177 :internal: 268 :internal:
178 269
179 .. kernel-doc:: drivers/gpu/drm/drm_print.c 270 .. kernel-doc:: drivers/gpu/drm/drm_print.c
180 :export: 271 :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 <<
222 272
223 273
224 Legacy Support Code 274 Legacy Support Code
225 =================== 275 ===================
226 276
227 The section very briefly covers some of the ol 277 The section very briefly covers some of the old legacy support code
228 which is only used by old DRM drivers which ha 278 which is only used by old DRM drivers which have done a so-called
229 shadow-attach to the underlying device instead 279 shadow-attach to the underlying device instead of registering as a real
230 driver. This also includes some of the old gen 280 driver. This also includes some of the old generic buffer management and
231 command submission code. Do not use any of thi 281 command submission code. Do not use any of this in new and modern
232 drivers. 282 drivers.
233 283
234 Legacy Suspend/Resume 284 Legacy Suspend/Resume
235 --------------------- 285 ---------------------
236 286
237 The DRM core provides some suspend/resume code 287 The DRM core provides some suspend/resume code, but drivers wanting full
238 suspend/resume support should provide save() a 288 suspend/resume support should provide save() and restore() functions.
239 These are called at suspend, hibernate, or res 289 These are called at suspend, hibernate, or resume time, and should
240 perform any state save or restore required by 290 perform any state save or restore required by your device across suspend
241 or hibernate states. 291 or hibernate states.
242 292
243 int (\*suspend) (struct drm_device \*, pm_mess 293 int (\*suspend) (struct drm_device \*, pm_message_t state); int
244 (\*resume) (struct drm_device \*); 294 (\*resume) (struct drm_device \*);
245 Those are legacy suspend and resume methods wh 295 Those are legacy suspend and resume methods which *only* work with the
246 legacy shadow-attach driver registration funct 296 legacy shadow-attach driver registration functions. New driver should
247 use the power management interface provided by 297 use the power management interface provided by their bus type (usually
248 through the :c:type:`struct device_driver <dev 298 through the :c:type:`struct device_driver <device_driver>`
249 dev_pm_ops) and set these methods to NULL. 299 dev_pm_ops) and set these methods to NULL.
250 300
251 Legacy DMA Services 301 Legacy DMA Services
252 ------------------- 302 -------------------
253 303
254 This should cover how DMA mapping etc. is supp 304 This should cover how DMA mapping etc. is supported by the core. These
255 functions are deprecated and should not be use 305 functions are deprecated and should not be used.
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