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
27:c:func:`drm_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 :c:func:`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