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 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 150Bus-specific Device Registration and PCI Support 151------------------------------------------------ 152 153A number of functions are provided to help with device registration. The 154functions deal with PCI and platform devices respectively and are only 155provided for historical reasons. These are all deprecated and shouldn't 156be used in new drivers. Besides that there's a few helpers for pci 157drivers. 158 159.. kernel-doc:: drivers/gpu/drm/drm_pci.c 160 :export: 161 162Open/Close, File Operations and IOCTLs 163====================================== 164 165.. _drm_driver_fops: 166 167File Operations 168--------------- 169 170.. kernel-doc:: drivers/gpu/drm/drm_file.c 171 :doc: file operations 172 173.. kernel-doc:: include/drm/drm_file.h 174 :internal: 175 176.. kernel-doc:: drivers/gpu/drm/drm_file.c 177 :export: 178 179Misc Utilities 180============== 181 182Printer 183------- 184 185.. kernel-doc:: include/drm/drm_print.h 186 :doc: print 187 188.. kernel-doc:: include/drm/drm_print.h 189 :internal: 190 191.. kernel-doc:: drivers/gpu/drm/drm_print.c 192 :export: 193 194Utilities 195--------- 196 197.. kernel-doc:: include/drm/drm_util.h 198 :doc: drm utils 199 200.. kernel-doc:: include/drm/drm_util.h 201 :internal: 202 203 204Legacy Support Code 205=================== 206 207The section very briefly covers some of the old legacy support code 208which is only used by old DRM drivers which have done a so-called 209shadow-attach to the underlying device instead of registering as a real 210driver. This also includes some of the old generic buffer management and 211command submission code. Do not use any of this in new and modern 212drivers. 213 214Legacy Suspend/Resume 215--------------------- 216 217The DRM core provides some suspend/resume code, but drivers wanting full 218suspend/resume support should provide save() and restore() functions. 219These are called at suspend, hibernate, or resume time, and should 220perform any state save or restore required by your device across suspend 221or hibernate states. 222 223int (\*suspend) (struct drm_device \*, pm_message_t state); int 224(\*resume) (struct drm_device \*); 225Those are legacy suspend and resume methods which *only* work with the 226legacy shadow-attach driver registration functions. New driver should 227use the power management interface provided by their bus type (usually 228through the :c:type:`struct device_driver <device_driver>` 229dev_pm_ops) and set these methods to NULL. 230 231Legacy DMA Services 232------------------- 233 234This should cover how DMA mapping etc. is supported by the core. These 235functions are deprecated and should not be used. 236