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 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 102IRQ Helper Library 103~~~~~~~~~~~~~~~~~~ 104 105.. kernel-doc:: drivers/gpu/drm/drm_irq.c 106 :doc: irq helpers 107 108.. kernel-doc:: drivers/gpu/drm/drm_irq.c 109 :export: 110 111Memory Manager Initialization 112~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 113 114Every DRM driver requires a memory manager which must be initialized at 115load time. DRM currently contains two memory managers, the Translation 116Table Manager (TTM) and the Graphics Execution Manager (GEM). This 117document describes the use of the GEM memory manager only. See ? for 118details. 119 120Miscellaneous Device Configuration 121~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 122 123Another task that may be necessary for PCI devices during configuration 124is mapping the video BIOS. On many devices, the VBIOS describes device 125configuration, LCD panel timings (if any), and contains flags indicating 126device state. Mapping the BIOS can be done using the pci_map_rom() 127call, a convenience function that takes care of mapping the actual ROM, 128whether it has been shadowed into memory (typically at address 0xc0000) 129or exists on the PCI device in the ROM BAR. Note that after the ROM has 130been mapped and any necessary information has been extracted, it should 131be unmapped; on many devices, the ROM address decoder is shared with 132other BARs, so leaving it mapped could cause undesired behaviour like 133hangs or memory corruption. 134 135Bus-specific Device Registration and PCI Support 136------------------------------------------------ 137 138A number of functions are provided to help with device registration. The 139functions deal with PCI and platform devices respectively and are only 140provided for historical reasons. These are all deprecated and shouldn't 141be used in new drivers. Besides that there's a few helpers for pci 142drivers. 143 144.. kernel-doc:: drivers/gpu/drm/drm_pci.c 145 :export: 146 147Open/Close, File Operations and IOCTLs 148====================================== 149 150.. _drm_driver_fops: 151 152File Operations 153--------------- 154 155.. kernel-doc:: drivers/gpu/drm/drm_file.c 156 :doc: file operations 157 158.. kernel-doc:: include/drm/drm_file.h 159 :internal: 160 161.. kernel-doc:: drivers/gpu/drm/drm_file.c 162 :export: 163 164Misc Utilities 165============== 166 167Printer 168------- 169 170.. kernel-doc:: include/drm/drm_print.h 171 :doc: print 172 173.. kernel-doc:: include/drm/drm_print.h 174 :internal: 175 176.. kernel-doc:: drivers/gpu/drm/drm_print.c 177 :export: 178 179Utilities 180--------- 181 182.. kernel-doc:: include/drm/drm_util.h 183 :doc: drm utils 184 185.. kernel-doc:: include/drm/drm_util.h 186 :internal: 187 188 189Legacy Support Code 190=================== 191 192The section very briefly covers some of the old legacy support code 193which is only used by old DRM drivers which have done a so-called 194shadow-attach to the underlying device instead of registering as a real 195driver. This also includes some of the old generic buffer management and 196command submission code. Do not use any of this in new and modern 197drivers. 198 199Legacy Suspend/Resume 200--------------------- 201 202The DRM core provides some suspend/resume code, but drivers wanting full 203suspend/resume support should provide save() and restore() functions. 204These are called at suspend, hibernate, or resume time, and should 205perform any state save or restore required by your device across suspend 206or hibernate states. 207 208int (\*suspend) (struct drm_device \*, pm_message_t state); int 209(\*resume) (struct drm_device \*); 210Those are legacy suspend and resume methods which *only* work with the 211legacy shadow-attach driver registration functions. New driver should 212use the power management interface provided by their bus type (usually 213through the :c:type:`struct device_driver <device_driver>` 214dev_pm_ops) and set these methods to NULL. 215 216Legacy DMA Services 217------------------- 218 219This should cover how DMA mapping etc. is supported by the core. These 220functions are deprecated and should not be used. 221