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