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 78Device Instance and Driver Handling 79----------------------------------- 80 81.. kernel-doc:: drivers/gpu/drm/drm_drv.c 82 :doc: driver instance overview 83 84.. kernel-doc:: include/drm/drm_device.h 85 :internal: 86 87.. kernel-doc:: include/drm/drm_drv.h 88 :internal: 89 90.. kernel-doc:: drivers/gpu/drm/drm_drv.c 91 :export: 92 93Driver Load 94----------- 95 96Component Helper Usage 97~~~~~~~~~~~~~~~~~~~~~~ 98 99.. kernel-doc:: drivers/gpu/drm/drm_drv.c 100 :doc: component helper usage recommendations 101 102Memory Manager Initialization 103~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 104 105Every DRM driver requires a memory manager which must be initialized at 106load time. DRM currently contains two memory managers, the Translation 107Table Manager (TTM) and the Graphics Execution Manager (GEM). This 108document describes the use of the GEM memory manager only. See ? for 109details. 110 111Miscellaneous Device Configuration 112~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 113 114Another task that may be necessary for PCI devices during configuration 115is mapping the video BIOS. On many devices, the VBIOS describes device 116configuration, LCD panel timings (if any), and contains flags indicating 117device state. Mapping the BIOS can be done using the pci_map_rom() 118call, a convenience function that takes care of mapping the actual ROM, 119whether it has been shadowed into memory (typically at address 0xc0000) 120or exists on the PCI device in the ROM BAR. Note that after the ROM has 121been mapped and any necessary information has been extracted, it should 122be unmapped; on many devices, the ROM address decoder is shared with 123other BARs, so leaving it mapped could cause undesired behaviour like 124hangs or memory corruption. 125 126Managed Resources 127----------------- 128 129.. kernel-doc:: drivers/gpu/drm/drm_managed.c 130 :doc: managed resources 131 132.. kernel-doc:: drivers/gpu/drm/drm_managed.c 133 :export: 134 135.. kernel-doc:: include/drm/drm_managed.h 136 :internal: 137 138Open/Close, File Operations and IOCTLs 139====================================== 140 141.. _drm_driver_fops: 142 143File Operations 144--------------- 145 146.. kernel-doc:: drivers/gpu/drm/drm_file.c 147 :doc: file operations 148 149.. kernel-doc:: include/drm/drm_file.h 150 :internal: 151 152.. kernel-doc:: drivers/gpu/drm/drm_file.c 153 :export: 154 155Misc Utilities 156============== 157 158Printer 159------- 160 161.. kernel-doc:: include/drm/drm_print.h 162 :doc: print 163 164.. kernel-doc:: include/drm/drm_print.h 165 :internal: 166 167.. kernel-doc:: drivers/gpu/drm/drm_print.c 168 :export: 169 170Utilities 171--------- 172 173.. kernel-doc:: include/drm/drm_util.h 174 :doc: drm utils 175 176.. kernel-doc:: include/drm/drm_util.h 177 :internal: 178 179 180Unit testing 181============ 182 183KUnit 184----- 185 186KUnit (Kernel unit testing framework) provides a common framework for unit tests 187within the Linux kernel. 188 189This section covers the specifics for the DRM subsystem. For general information 190about KUnit, please refer to Documentation/dev-tools/kunit/start.rst. 191 192How to run the tests? 193~~~~~~~~~~~~~~~~~~~~~ 194 195In order to facilitate running the test suite, a configuration file is present 196in ``drivers/gpu/drm/tests/.kunitconfig``. It can be used by ``kunit.py`` as 197follows: 198 199.. code-block:: bash 200 201 $ ./tools/testing/kunit/kunit.py run --kunitconfig=drivers/gpu/drm/tests \ 202 --kconfig_add CONFIG_VIRTIO_UML=y \ 203 --kconfig_add CONFIG_UML_PCI_OVER_VIRTIO=y 204 205.. note:: 206 The configuration included in ``.kunitconfig`` should be as generic as 207 possible. 208 ``CONFIG_VIRTIO_UML`` and ``CONFIG_UML_PCI_OVER_VIRTIO`` are not 209 included in it because they are only required for User Mode Linux. 210 211 212Legacy Support Code 213=================== 214 215The section very briefly covers some of the old legacy support code 216which is only used by old DRM drivers which have done a so-called 217shadow-attach to the underlying device instead of registering as a real 218driver. This also includes some of the old generic buffer management and 219command submission code. Do not use any of this in new and modern 220drivers. 221 222Legacy Suspend/Resume 223--------------------- 224 225The DRM core provides some suspend/resume code, but drivers wanting full 226suspend/resume support should provide save() and restore() functions. 227These are called at suspend, hibernate, or resume time, and should 228perform any state save or restore required by your device across suspend 229or hibernate states. 230 231int (\*suspend) (struct drm_device \*, pm_message_t state); int 232(\*resume) (struct drm_device \*); 233Those are legacy suspend and resume methods which *only* work with the 234legacy shadow-attach driver registration functions. New driver should 235use the power management interface provided by their bus type (usually 236through the :c:type:`struct device_driver <device_driver>` 237dev_pm_ops) and set these methods to NULL. 238 239Legacy DMA Services 240------------------- 241 242This should cover how DMA mapping etc. is supported by the core. These 243functions are deprecated and should not be used. 244