1============= 2DRM Internals 3============= 4 5This chapter documents DRM internals relevant to driver authors and 6developers working to add support for the latest features to existing 7drivers. 8 9First, we go over some typical driver initialization requirements, like 10setting up command buffers, creating an initial output configuration, 11and initializing core services. Subsequent sections cover core internals 12in more detail, providing implementation notes and examples. 13 14The DRM layer provides several services to graphics drivers, many of 15them driven by the application interfaces it provides through libdrm, 16the library that wraps most of the DRM ioctls. These include vblank 17event handling, memory management, output management, framebuffer 18management, command submission & fencing, suspend/resume support, and 19DMA services. 20 21Driver Initialization 22===================== 23 24At the core of every DRM driver is a :c:type:`struct drm_driver 25<drm_driver>` structure. Drivers typically statically initialize 26a drm_driver structure, and then pass it to 27drm_dev_alloc() to allocate a device instance. After the 28device instance is fully initialized it can be registered (which makes 29it accessible from userspace) using drm_dev_register(). 30 31The :c:type:`struct drm_driver <drm_driver>` structure 32contains static information that describes the driver and features it 33supports, and pointers to methods that the DRM core will call to 34implement the DRM API. We will first go through the :c:type:`struct 35drm_driver <drm_driver>` static information fields, and will 36then describe individual operations in details as they get used in later 37sections. 38 39Driver Information 40------------------ 41 42Major, Minor and Patchlevel 43~~~~~~~~~~~~~~~~~~~~~~~~~~~ 44 45int major; int minor; int patchlevel; 46The DRM core identifies driver versions by a major, minor and patch 47level triplet. The information is printed to the kernel log at 48initialization time and passed to userspace through the 49DRM_IOCTL_VERSION ioctl. 50 51The major and minor numbers are also used to verify the requested driver 52API version passed to DRM_IOCTL_SET_VERSION. When the driver API 53changes between minor versions, applications can call 54DRM_IOCTL_SET_VERSION to select a specific version of the API. If the 55requested major isn't equal to the driver major, or the requested minor 56is larger than the driver minor, the DRM_IOCTL_SET_VERSION call will 57return an error. Otherwise the driver's set_version() method will be 58called with the requested version. 59 60Name, Description and Date 61~~~~~~~~~~~~~~~~~~~~~~~~~~ 62 63char \*name; char \*desc; char \*date; 64The driver name is printed to the kernel log at initialization time, 65used for IRQ registration and passed to userspace through 66DRM_IOCTL_VERSION. 67 68The driver description is a purely informative string passed to 69userspace through the DRM_IOCTL_VERSION ioctl and otherwise unused by 70the kernel. 71 72The driver date, formatted as YYYYMMDD, is meant to identify the date of 73the latest modification to the driver. However, as most drivers fail to 74update it, its value is mostly useless. The DRM core prints it to the 75kernel log at initialization time and passes it to userspace through the 76DRM_IOCTL_VERSION ioctl. 77 78Module Initialization 79--------------------- 80 81.. kernel-doc:: include/drm/drm_module.h 82 :doc: overview 83 84Managing Ownership of the Framebuffer Aperture 85---------------------------------------------- 86 87.. kernel-doc:: drivers/gpu/drm/drm_aperture.c 88 :doc: overview 89 90.. kernel-doc:: include/drm/drm_aperture.h 91 :internal: 92 93.. kernel-doc:: drivers/gpu/drm/drm_aperture.c 94 :export: 95 96Device Instance and Driver Handling 97----------------------------------- 98 99.. kernel-doc:: drivers/gpu/drm/drm_drv.c 100 :doc: driver instance overview 101 102.. kernel-doc:: include/drm/drm_device.h 103 :internal: 104 105.. kernel-doc:: include/drm/drm_drv.h 106 :internal: 107 108.. kernel-doc:: drivers/gpu/drm/drm_drv.c 109 :export: 110 111Driver Load 112----------- 113 114Component Helper Usage 115~~~~~~~~~~~~~~~~~~~~~~ 116 117.. kernel-doc:: drivers/gpu/drm/drm_drv.c 118 :doc: component helper usage recommendations 119 120Memory Manager Initialization 121~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 122 123Every DRM driver requires a memory manager which must be initialized at 124load time. DRM currently contains two memory managers, the Translation 125Table Manager (TTM) and the Graphics Execution Manager (GEM). This 126document describes the use of the GEM memory manager only. See ? for 127details. 128 129Miscellaneous Device Configuration 130~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 131 132Another task that may be necessary for PCI devices during configuration 133is mapping the video BIOS. On many devices, the VBIOS describes device 134configuration, LCD panel timings (if any), and contains flags indicating 135device state. Mapping the BIOS can be done using the pci_map_rom() 136call, a convenience function that takes care of mapping the actual ROM, 137whether it has been shadowed into memory (typically at address 0xc0000) 138or exists on the PCI device in the ROM BAR. Note that after the ROM has 139been mapped and any necessary information has been extracted, it should 140be unmapped; on many devices, the ROM address decoder is shared with 141other BARs, so leaving it mapped could cause undesired behaviour like 142hangs or memory corruption. 143 144Managed Resources 145----------------- 146 147.. kernel-doc:: drivers/gpu/drm/drm_managed.c 148 :doc: managed resources 149 150.. kernel-doc:: drivers/gpu/drm/drm_managed.c 151 :export: 152 153.. kernel-doc:: include/drm/drm_managed.h 154 :internal: 155 156Bus-specific Device Registration and PCI Support 157------------------------------------------------ 158 159A number of functions are provided to help with device registration. The 160functions deal with PCI and platform devices respectively and are only 161provided for historical reasons. These are all deprecated and shouldn't 162be used in new drivers. Besides that there's a few helpers for pci 163drivers. 164 165.. kernel-doc:: drivers/gpu/drm/drm_pci.c 166 :export: 167 168Open/Close, File Operations and IOCTLs 169====================================== 170 171.. _drm_driver_fops: 172 173File Operations 174--------------- 175 176.. kernel-doc:: drivers/gpu/drm/drm_file.c 177 :doc: file operations 178 179.. kernel-doc:: include/drm/drm_file.h 180 :internal: 181 182.. kernel-doc:: drivers/gpu/drm/drm_file.c 183 :export: 184 185Misc Utilities 186============== 187 188Printer 189------- 190 191.. kernel-doc:: include/drm/drm_print.h 192 :doc: print 193 194.. kernel-doc:: include/drm/drm_print.h 195 :internal: 196 197.. kernel-doc:: drivers/gpu/drm/drm_print.c 198 :export: 199 200Utilities 201--------- 202 203.. kernel-doc:: include/drm/drm_util.h 204 :doc: drm utils 205 206.. kernel-doc:: include/drm/drm_util.h 207 :internal: 208 209 210Unit testing 211============ 212 213KUnit 214----- 215 216KUnit (Kernel unit testing framework) provides a common framework for unit tests 217within the Linux kernel. 218 219This section covers the specifics for the DRM subsystem. For general information 220about KUnit, please refer to Documentation/dev-tools/kunit/start.rst. 221 222How to run the tests? 223~~~~~~~~~~~~~~~~~~~~~ 224 225In order to facilitate running the test suite, a configuration file is present 226in ``drivers/gpu/drm/tests/.kunitconfig``. It can be used by ``kunit.py`` as 227follows: 228 229.. code-block:: bash 230 231 $ ./tools/testing/kunit/kunit.py run --kunitconfig=drivers/gpu/drm/tests \ 232 --kconfig_add CONFIG_VIRTIO_UML=y \ 233 --kconfig_add CONFIG_UML_PCI_OVER_VIRTIO=y 234 235.. note:: 236 The configuration included in ``.kunitconfig`` should be as generic as 237 possible. 238 ``CONFIG_VIRTIO_UML`` and ``CONFIG_UML_PCI_OVER_VIRTIO`` are not 239 included in it because they are only required for User Mode Linux. 240 241 242Legacy Support Code 243=================== 244 245The section very briefly covers some of the old legacy support code 246which is only used by old DRM drivers which have done a so-called 247shadow-attach to the underlying device instead of registering as a real 248driver. This also includes some of the old generic buffer management and 249command submission code. Do not use any of this in new and modern 250drivers. 251 252Legacy Suspend/Resume 253--------------------- 254 255The DRM core provides some suspend/resume code, but drivers wanting full 256suspend/resume support should provide save() and restore() functions. 257These are called at suspend, hibernate, or resume time, and should 258perform any state save or restore required by your device across suspend 259or hibernate states. 260 261int (\*suspend) (struct drm_device \*, pm_message_t state); int 262(\*resume) (struct drm_device \*); 263Those are legacy suspend and resume methods which *only* work with the 264legacy shadow-attach driver registration functions. New driver should 265use the power management interface provided by their bus type (usually 266through the :c:type:`struct device_driver <device_driver>` 267dev_pm_ops) and set these methods to NULL. 268 269Legacy DMA Services 270------------------- 271 272This should cover how DMA mapping etc. is supported by the core. These 273functions are deprecated and should not be used. 274