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22554020 | 1 | ============= |
ca00c2b9 JN |
2 | DRM Internals |
3 | ============= | |
4 | ||
5 | This chapter documents DRM internals relevant to driver authors and | |
6 | developers working to add support for the latest features to existing | |
7 | drivers. | |
8 | ||
9 | First, we go over some typical driver initialization requirements, like | |
10 | setting up command buffers, creating an initial output configuration, | |
11 | and initializing core services. Subsequent sections cover core internals | |
12 | in more detail, providing implementation notes and examples. | |
13 | ||
14 | The DRM layer provides several services to graphics drivers, many of | |
15 | them driven by the application interfaces it provides through libdrm, | |
16 | the library that wraps most of the DRM ioctls. These include vblank | |
17 | event handling, memory management, output management, framebuffer | |
18 | management, command submission & fencing, suspend/resume support, and | |
19 | DMA services. | |
20 | ||
21 | Driver Initialization | |
22554020 | 22 | ===================== |
ca00c2b9 JN |
23 | |
24 | At the core of every DRM driver is a :c:type:`struct drm_driver | |
25 | <drm_driver>` structure. Drivers typically statically initialize | |
26 | a drm_driver structure, and then pass it to | |
27 | :c:func:`drm_dev_alloc()` to allocate a device instance. After the | |
28 | device instance is fully initialized it can be registered (which makes | |
29 | it accessible from userspace) using :c:func:`drm_dev_register()`. | |
30 | ||
31 | The :c:type:`struct drm_driver <drm_driver>` structure | |
32 | contains static information that describes the driver and features it | |
33 | supports, and pointers to methods that the DRM core will call to | |
34 | implement the DRM API. We will first go through the :c:type:`struct | |
35 | drm_driver <drm_driver>` static information fields, and will | |
36 | then describe individual operations in details as they get used in later | |
37 | sections. | |
38 | ||
39 | Driver Information | |
22554020 | 40 | ------------------ |
ca00c2b9 | 41 | |
ca00c2b9 | 42 | Major, Minor and Patchlevel |
2fa91d15 | 43 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
ca00c2b9 JN |
44 | |
45 | int major; int minor; int patchlevel; | |
46 | The DRM core identifies driver versions by a major, minor and patch | |
47 | level triplet. The information is printed to the kernel log at | |
48 | initialization time and passed to userspace through the | |
49 | DRM_IOCTL_VERSION ioctl. | |
50 | ||
51 | The major and minor numbers are also used to verify the requested driver | |
52 | API version passed to DRM_IOCTL_SET_VERSION. When the driver API | |
53 | changes between minor versions, applications can call | |
54 | DRM_IOCTL_SET_VERSION to select a specific version of the API. If the | |
55 | requested major isn't equal to the driver major, or the requested minor | |
56 | is larger than the driver minor, the DRM_IOCTL_SET_VERSION call will | |
57 | return an error. Otherwise the driver's set_version() method will be | |
58 | called with the requested version. | |
59 | ||
60 | Name, Description and Date | |
2fa91d15 | 61 | ~~~~~~~~~~~~~~~~~~~~~~~~~~ |
ca00c2b9 JN |
62 | |
63 | char \*name; char \*desc; char \*date; | |
64 | The driver name is printed to the kernel log at initialization time, | |
65 | used for IRQ registration and passed to userspace through | |
66 | DRM_IOCTL_VERSION. | |
67 | ||
68 | The driver description is a purely informative string passed to | |
69 | userspace through the DRM_IOCTL_VERSION ioctl and otherwise unused by | |
70 | the kernel. | |
71 | ||
72 | The driver date, formatted as YYYYMMDD, is meant to identify the date of | |
73 | the latest modification to the driver. However, as most drivers fail to | |
74 | update it, its value is mostly useless. The DRM core prints it to the | |
75 | kernel log at initialization time and passes it to userspace through the | |
76 | DRM_IOCTL_VERSION ioctl. | |
77 | ||
78 | Device Instance and Driver Handling | |
22554020 | 79 | ----------------------------------- |
ca00c2b9 JN |
80 | |
81 | .. kernel-doc:: drivers/gpu/drm/drm_drv.c | |
82 | :doc: driver instance overview | |
83 | ||
3214a166 DV |
84 | .. kernel-doc:: include/drm/drm_device.h |
85 | :internal: | |
86 | ||
6c4789ed DV |
87 | .. kernel-doc:: include/drm/drm_drv.h |
88 | :internal: | |
89 | ||
1ea35768 DV |
90 | .. kernel-doc:: drivers/gpu/drm/drm_drv.c |
91 | :export: | |
92 | ||
ca00c2b9 | 93 | Driver Load |
22554020 | 94 | ----------- |
ca00c2b9 | 95 | |
ca00c2b9 | 96 | |
3ed4351a DV |
97 | IRQ Helper Library |
98 | ~~~~~~~~~~~~~~~~~~ | |
99 | ||
100 | .. kernel-doc:: drivers/gpu/drm/drm_irq.c | |
101 | :doc: irq helpers | |
102 | ||
103 | .. kernel-doc:: drivers/gpu/drm/drm_irq.c | |
104 | :export: | |
105 | ||
ca00c2b9 | 106 | Memory Manager Initialization |
2fa91d15 | 107 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
ca00c2b9 JN |
108 | |
109 | Every DRM driver requires a memory manager which must be initialized at | |
110 | load time. DRM currently contains two memory managers, the Translation | |
111 | Table Manager (TTM) and the Graphics Execution Manager (GEM). This | |
112 | document describes the use of the GEM memory manager only. See ? for | |
113 | details. | |
114 | ||
115 | Miscellaneous Device Configuration | |
2fa91d15 | 116 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
ca00c2b9 JN |
117 | |
118 | Another task that may be necessary for PCI devices during configuration | |
119 | is mapping the video BIOS. On many devices, the VBIOS describes device | |
120 | configuration, LCD panel timings (if any), and contains flags indicating | |
121 | device state. Mapping the BIOS can be done using the pci_map_rom() | |
122 | call, a convenience function that takes care of mapping the actual ROM, | |
123 | whether it has been shadowed into memory (typically at address 0xc0000) | |
124 | or exists on the PCI device in the ROM BAR. Note that after the ROM has | |
125 | been mapped and any necessary information has been extracted, it should | |
126 | be unmapped; on many devices, the ROM address decoder is shared with | |
127 | other BARs, so leaving it mapped could cause undesired behaviour like | |
128 | hangs or memory corruption. | |
129 | ||
130 | Bus-specific Device Registration and PCI Support | |
22554020 | 131 | ------------------------------------------------ |
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132 | |
133 | A number of functions are provided to help with device registration. The | |
134 | functions deal with PCI and platform devices respectively and are only | |
135 | provided for historical reasons. These are all deprecated and shouldn't | |
136 | be used in new drivers. Besides that there's a few helpers for pci | |
137 | drivers. | |
138 | ||
139 | .. kernel-doc:: drivers/gpu/drm/drm_pci.c | |
140 | :export: | |
141 | ||
ca00c2b9 | 142 | Open/Close, File Operations and IOCTLs |
22554020 | 143 | ====================================== |
ca00c2b9 | 144 | |
bb2eaba6 DV |
145 | .. _drm_driver_fops: |
146 | ||
ca00c2b9 | 147 | File Operations |
22554020 | 148 | --------------- |
ca00c2b9 | 149 | |
9acdac68 | 150 | .. kernel-doc:: drivers/gpu/drm/drm_file.c |
ca00c2b9 JN |
151 | :doc: file operations |
152 | ||
b93658f8 DV |
153 | .. kernel-doc:: include/drm/drm_file.h |
154 | :internal: | |
155 | ||
9acdac68 | 156 | .. kernel-doc:: drivers/gpu/drm/drm_file.c |
ca00c2b9 JN |
157 | :export: |
158 | ||
d8187177 RC |
159 | Misc Utilities |
160 | ============== | |
161 | ||
162 | Printer | |
163 | ------- | |
164 | ||
165 | .. kernel-doc:: include/drm/drm_print.h | |
166 | :doc: print | |
167 | ||
168 | .. kernel-doc:: include/drm/drm_print.h | |
169 | :internal: | |
170 | ||
2d5e836d | 171 | .. kernel-doc:: drivers/gpu/drm/drm_print.c |
d8187177 RC |
172 | :export: |
173 | ||
e9eafcb5 SR |
174 | Utilities |
175 | --------- | |
176 | ||
177 | .. kernel-doc:: include/drm/drm_util.h | |
178 | :doc: drm utils | |
179 | ||
180 | .. kernel-doc:: include/drm/drm_util.h | |
181 | :internal: | |
182 | ||
d8187177 | 183 | |
ca00c2b9 | 184 | Legacy Support Code |
22554020 | 185 | =================== |
ca00c2b9 JN |
186 | |
187 | The section very briefly covers some of the old legacy support code | |
188 | which is only used by old DRM drivers which have done a so-called | |
189 | shadow-attach to the underlying device instead of registering as a real | |
190 | driver. This also includes some of the old generic buffer management and | |
191 | command submission code. Do not use any of this in new and modern | |
192 | drivers. | |
193 | ||
194 | Legacy Suspend/Resume | |
22554020 | 195 | --------------------- |
ca00c2b9 JN |
196 | |
197 | The DRM core provides some suspend/resume code, but drivers wanting full | |
198 | suspend/resume support should provide save() and restore() functions. | |
199 | These are called at suspend, hibernate, or resume time, and should | |
200 | perform any state save or restore required by your device across suspend | |
201 | or hibernate states. | |
202 | ||
203 | int (\*suspend) (struct drm_device \*, pm_message_t state); int | |
204 | (\*resume) (struct drm_device \*); | |
205 | Those are legacy suspend and resume methods which *only* work with the | |
206 | legacy shadow-attach driver registration functions. New driver should | |
207 | use the power management interface provided by their bus type (usually | |
208 | through the :c:type:`struct device_driver <device_driver>` | |
209 | dev_pm_ops) and set these methods to NULL. | |
210 | ||
211 | Legacy DMA Services | |
22554020 | 212 | ------------------- |
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213 | |
214 | This should cover how DMA mapping etc. is supported by the core. These | |
215 | functions are deprecated and should not be used. |