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 and Description 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 72Module Initialization 73--------------------- 74 75.. kernel-doc:: include/drm/drm_module.h 76 :doc: overview 77 78Managing 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 90Device 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 105Driver Load 106----------- 107 108Component Helper Usage 109~~~~~~~~~~~~~~~~~~~~~~ 110 111.. kernel-doc:: drivers/gpu/drm/drm_drv.c 112 :doc: component helper usage recommendations 113 114Memory Manager Initialization 115~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 116 117Every DRM driver requires a memory manager which must be initialized at 118load time. DRM currently contains two memory managers, the Translation 119Table Manager (TTM) and the Graphics Execution Manager (GEM). This 120document describes the use of the GEM memory manager only. See ? for 121details. 122 123Miscellaneous Device Configuration 124~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 125 126Another task that may be necessary for PCI devices during configuration 127is mapping the video BIOS. On many devices, the VBIOS describes device 128configuration, LCD panel timings (if any), and contains flags indicating 129device state. Mapping the BIOS can be done using the pci_map_rom() 130call, a convenience function that takes care of mapping the actual ROM, 131whether it has been shadowed into memory (typically at address 0xc0000) 132or exists on the PCI device in the ROM BAR. Note that after the ROM has 133been mapped and any necessary information has been extracted, it should 134be unmapped; on many devices, the ROM address decoder is shared with 135other BARs, so leaving it mapped could cause undesired behaviour like 136hangs or memory corruption. 137 138Managed 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 150Open/Close, File Operations and IOCTLs 151====================================== 152 153.. _drm_driver_fops: 154 155File 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 167Misc Utilities 168============== 169 170Printer 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 182Utilities 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 192Unit testing 193============ 194 195KUnit 196----- 197 198KUnit (Kernel unit testing framework) provides a common framework for unit tests 199within the Linux kernel. 200 201This section covers the specifics for the DRM subsystem. For general information 202about KUnit, please refer to Documentation/dev-tools/kunit/start.rst. 203 204How to run the tests? 205~~~~~~~~~~~~~~~~~~~~~ 206 207In order to facilitate running the test suite, a configuration file is present 208in ``drivers/gpu/drm/tests/.kunitconfig``. It can be used by ``kunit.py`` as 209follows: 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 224Legacy Support Code 225=================== 226 227The section very briefly covers some of the old legacy support code 228which is only used by old DRM drivers which have done a so-called 229shadow-attach to the underlying device instead of registering as a real 230driver. This also includes some of the old generic buffer management and 231command submission code. Do not use any of this in new and modern 232drivers. 233 234Legacy Suspend/Resume 235--------------------- 236 237The DRM core provides some suspend/resume code, but drivers wanting full 238suspend/resume support should provide save() and restore() functions. 239These are called at suspend, hibernate, or resume time, and should 240perform any state save or restore required by your device across suspend 241or hibernate states. 242 243int (\*suspend) (struct drm_device \*, pm_message_t state); int 244(\*resume) (struct drm_device \*); 245Those are legacy suspend and resume methods which *only* work with the 246legacy shadow-attach driver registration functions. New driver should 247use the power management interface provided by their bus type (usually 248through the :c:type:`struct device_driver <device_driver>` 249dev_pm_ops) and set these methods to NULL. 250 251Legacy DMA Services 252------------------- 253 254This should cover how DMA mapping etc. is supported by the core. These 255functions are deprecated and should not be used. 256