1 ============= 2 DRM Internals 3 ============= 4 5 This chapter documents DRM internals relevant to driver authors and 6 developers working to add support for the latest features to existing 7 drivers. 8 9 First, we go over some typical driver initialization requirements, like 10 setting up command buffers, creating an initial output configuration, 11 and initializing core services. Subsequent sections cover core internals 12 in more detail, providing implementation notes and examples. 13 14 The DRM layer provides several services to graphics drivers, many of 15 them driven by the application interfaces it provides through libdrm, 16 the library that wraps most of the DRM ioctls. These include vblank 17 event handling, memory management, output management, framebuffer 18 management, command submission & fencing, suspend/resume support, and 19 DMA services. 20 21 Driver Initialization 22 ===================== 23 24 At the core of every DRM driver is a :c:type:`struct drm_driver 25 <drm_driver>` structure. Drivers typically statically initialize 26 a drm_driver structure, and then pass it to 27 drm_dev_alloc() to allocate a device instance. After the 28 device instance is fully initialized it can be registered (which makes 29 it accessible from userspace) using drm_dev_register(). 30 31 The :c:type:`struct drm_driver <drm_driver>` structure 32 contains static information that describes the driver and features it 33 supports, and pointers to methods that the DRM core will call to 34 implement the DRM API. We will first go through the :c:type:`struct 35 drm_driver <drm_driver>` static information fields, and will 36 then describe individual operations in details as they get used in later 37 sections. 38 39 Driver Information 40 ------------------ 41 42 Major, Minor and Patchlevel 43 ~~~~~~~~~~~~~~~~~~~~~~~~~~~ 44 45 int major; int minor; int patchlevel; 46 The DRM core identifies driver versions by a major, minor and patch 47 level triplet. The information is printed to the kernel log at 48 initialization time and passed to userspace through the 49 DRM_IOCTL_VERSION ioctl. 50 51 The major and minor numbers are also used to verify the requested driver 52 API version passed to DRM_IOCTL_SET_VERSION. When the driver API 53 changes between minor versions, applications can call 54 DRM_IOCTL_SET_VERSION to select a specific version of the API. If the 55 requested major isn't equal to the driver major, or the requested minor 56 is larger than the driver minor, the DRM_IOCTL_SET_VERSION call will 57 return an error. Otherwise the driver's set_version() method will be 58 called with the requested version. 59 60 Name and Description 61 ~~~~~~~~~~~~~~~~~~~~ 62 63 char \*name; char \*desc; char \*date; 64 The driver name is printed to the kernel log at initialization time, 65 used for IRQ registration and passed to userspace through 66 DRM_IOCTL_VERSION. 67 68 The driver description is a purely informative string passed to 69 userspace through the DRM_IOCTL_VERSION ioctl and otherwise unused by 70 the kernel. 71 72 Module Initialization 73 --------------------- 74 75 .. kernel-doc:: include/drm/drm_module.h 76 :doc: overview 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 90 Device Instance and Driver Handling 91 ----------------------------------- 92 93 .. kernel-doc:: drivers/gpu/drm/drm_drv.c 94 :doc: driver instance overview 95 96 .. kernel-doc:: include/drm/drm_device.h 97 :internal: 98 99 .. kernel-doc:: include/drm/drm_drv.h 100 :internal: 101 102 .. kernel-doc:: drivers/gpu/drm/drm_drv.c 103 :export: 104 105 Driver Load 106 ----------- 107 108 Component Helper Usage 109 ~~~~~~~~~~~~~~~~~~~~~~ 110 111 .. kernel-doc:: drivers/gpu/drm/drm_drv.c 112 :doc: component helper usage recommendations 113 114 Memory Manager Initialization 115 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 116 117 Every DRM driver requires a memory manager which must be initialized at 118 load time. DRM currently contains two memory managers, the Translation 119 Table Manager (TTM) and the Graphics Execution Manager (GEM). This 120 document describes the use of the GEM memory manager only. See ? for 121 details. 122 123 Miscellaneous Device Configuration 124 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 125 126 Another task that may be necessary for PCI devices during configuration 127 is mapping the video BIOS. On many devices, the VBIOS describes device 128 configuration, LCD panel timings (if any), and contains flags indicating 129 device state. Mapping the BIOS can be done using the pci_map_rom() 130 call, a convenience function that takes care of mapping the actual ROM, 131 whether it has been shadowed into memory (typically at address 0xc0000) 132 or exists on the PCI device in the ROM BAR. Note that after the ROM has 133 been mapped and any necessary information has been extracted, it should 134 be unmapped; on many devices, the ROM address decoder is shared with 135 other BARs, so leaving it mapped could cause undesired behaviour like 136 hangs or memory corruption. 137 138 Managed Resources 139 ----------------- 140 141 .. kernel-doc:: drivers/gpu/drm/drm_managed.c 142 :doc: managed resources 143 144 .. kernel-doc:: drivers/gpu/drm/drm_managed.c 145 :export: 146 147 .. kernel-doc:: include/drm/drm_managed.h 148 :internal: 149 150 Open/Close, File Operations and IOCTLs 151 ====================================== 152 153 .. _drm_driver_fops: 154 155 File Operations 156 --------------- 157 158 .. kernel-doc:: drivers/gpu/drm/drm_file.c 159 :doc: file operations 160 161 .. kernel-doc:: include/drm/drm_file.h 162 :internal: 163 164 .. kernel-doc:: drivers/gpu/drm/drm_file.c 165 :export: 166 167 Misc Utilities 168 ============== 169 170 Printer 171 ------- 172 173 .. kernel-doc:: include/drm/drm_print.h 174 :doc: print 175 176 .. kernel-doc:: include/drm/drm_print.h 177 :internal: 178 179 .. kernel-doc:: drivers/gpu/drm/drm_print.c 180 :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 a common framework for unit tests 199 within the Linux kernel. 200 201 This section covers the specifics for the DRM subsystem. For general information 202 about KUnit, please refer to Documentation/dev-tools/kunit/start.rst. 203 204 How to run the tests? 205 ~~~~~~~~~~~~~~~~~~~~~ 206 207 In order to facilitate running the test suite, a configuration file is present 208 in ``drivers/gpu/drm/tests/.kunitconfig``. It can be used by ``kunit.py`` as 209 follows: 210 211 .. code-block:: bash 212 213 $ ./tools/testing/kunit/kunit.py run --kunitconfig=drivers/gpu/drm/tests \ 214 --kconfig_add CONFIG_VIRTIO_UML=y \ 215 --kconfig_add CONFIG_UML_PCI_OVER_VIRTIO=y 216 217 .. note:: 218 The configuration included in ``.kunitconfig`` should be as generic as 219 possible. 220 ``CONFIG_VIRTIO_UML`` and ``CONFIG_UML_PCI_OVER_VIRTIO`` are not 221 included in it because they are only required for User Mode Linux. 222 223 224 Legacy Support Code 225 =================== 226 227 The section very briefly covers some of the old legacy support code 228 which is only used by old DRM drivers which have done a so-called 229 shadow-attach to the underlying device instead of registering as a real 230 driver. This also includes some of the old generic buffer management and 231 command submission code. Do not use any of this in new and modern 232 drivers. 233 234 Legacy Suspend/Resume 235 --------------------- 236 237 The DRM core provides some suspend/resume code, but drivers wanting full 238 suspend/resume support should provide save() and restore() functions. 239 These are called at suspend, hibernate, or resume time, and should 240 perform any state save or restore required by your device across suspend 241 or hibernate states. 242 243 int (\*suspend) (struct drm_device \*, pm_message_t state); int 244 (\*resume) (struct drm_device \*); 245 Those are legacy suspend and resume methods which *only* work with the 246 legacy shadow-attach driver registration functions. New driver should 247 use the power management interface provided by their bus type (usually 248 through the :c:type:`struct device_driver <device_driver>` 249 dev_pm_ops) and set these methods to NULL. 250 251 Legacy DMA Services 252 ------------------- 253 254 This should cover how DMA mapping etc. is supported by the core. These 255 functions are deprecated and should not be used.
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