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
114IRQ Helper Library
115~~~~~~~~~~~~~~~~~~
116
117.. kernel-doc:: drivers/gpu/drm/drm_irq.c
118   :doc: irq helpers
119
120.. kernel-doc:: drivers/gpu/drm/drm_irq.c
121   :export:
122
123Memory Manager Initialization
124~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
125
126Every DRM driver requires a memory manager which must be initialized at
127load time. DRM currently contains two memory managers, the Translation
128Table Manager (TTM) and the Graphics Execution Manager (GEM). This
129document describes the use of the GEM memory manager only. See ? for
130details.
131
132Miscellaneous Device Configuration
133~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
134
135Another task that may be necessary for PCI devices during configuration
136is mapping the video BIOS. On many devices, the VBIOS describes device
137configuration, LCD panel timings (if any), and contains flags indicating
138device state. Mapping the BIOS can be done using the pci_map_rom()
139call, a convenience function that takes care of mapping the actual ROM,
140whether it has been shadowed into memory (typically at address 0xc0000)
141or exists on the PCI device in the ROM BAR. Note that after the ROM has
142been mapped and any necessary information has been extracted, it should
143be unmapped; on many devices, the ROM address decoder is shared with
144other BARs, so leaving it mapped could cause undesired behaviour like
145hangs or memory corruption.
146
147Managed Resources
148-----------------
149
150.. kernel-doc:: drivers/gpu/drm/drm_managed.c
151   :doc: managed resources
152
153.. kernel-doc:: drivers/gpu/drm/drm_managed.c
154   :export:
155
156.. kernel-doc:: include/drm/drm_managed.h
157   :internal:
158
159Bus-specific Device Registration and PCI Support
160------------------------------------------------
161
162A number of functions are provided to help with device registration. The
163functions deal with PCI and platform devices respectively and are only
164provided for historical reasons. These are all deprecated and shouldn't
165be used in new drivers. Besides that there's a few helpers for pci
166drivers.
167
168.. kernel-doc:: drivers/gpu/drm/drm_pci.c
169   :export:
170
171Open/Close, File Operations and IOCTLs
172======================================
173
174.. _drm_driver_fops:
175
176File Operations
177---------------
178
179.. kernel-doc:: drivers/gpu/drm/drm_file.c
180   :doc: file operations
181
182.. kernel-doc:: include/drm/drm_file.h
183   :internal:
184
185.. kernel-doc:: drivers/gpu/drm/drm_file.c
186   :export:
187
188Misc Utilities
189==============
190
191Printer
192-------
193
194.. kernel-doc:: include/drm/drm_print.h
195   :doc: print
196
197.. kernel-doc:: include/drm/drm_print.h
198   :internal:
199
200.. kernel-doc:: drivers/gpu/drm/drm_print.c
201   :export:
202
203Utilities
204---------
205
206.. kernel-doc:: include/drm/drm_util.h
207   :doc: drm utils
208
209.. kernel-doc:: include/drm/drm_util.h
210   :internal:
211
212
213Legacy Support Code
214===================
215
216The section very briefly covers some of the old legacy support code
217which is only used by old DRM drivers which have done a so-called
218shadow-attach to the underlying device instead of registering as a real
219driver. This also includes some of the old generic buffer management and
220command submission code. Do not use any of this in new and modern
221drivers.
222
223Legacy Suspend/Resume
224---------------------
225
226The DRM core provides some suspend/resume code, but drivers wanting full
227suspend/resume support should provide save() and restore() functions.
228These are called at suspend, hibernate, or resume time, and should
229perform any state save or restore required by your device across suspend
230or hibernate states.
231
232int (\*suspend) (struct drm_device \*, pm_message_t state); int
233(\*resume) (struct drm_device \*);
234Those are legacy suspend and resume methods which *only* work with the
235legacy shadow-attach driver registration functions. New driver should
236use the power management interface provided by their bus type (usually
237through the :c:type:`struct device_driver <device_driver>`
238dev_pm_ops) and set these methods to NULL.
239
240Legacy DMA Services
241-------------------
242
243This should cover how DMA mapping etc. is supported by the core. These
244functions are deprecated and should not be used.
245