Loading...
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 and Description
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
72Module Initialization
73---------------------
74
75.. kernel-doc:: include/drm/drm_module.h
76 :doc: overview
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
102Memory Manager Initialization
103~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
104
105Every DRM driver requires a memory manager which must be initialized at
106load time. DRM currently contains two memory managers, the Translation
107Table Manager (TTM) and the Graphics Execution Manager (GEM). This
108document describes the use of the GEM memory manager only. See ? for
109details.
110
111Miscellaneous Device Configuration
112~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
113
114Another task that may be necessary for PCI devices during configuration
115is mapping the video BIOS. On many devices, the VBIOS describes device
116configuration, LCD panel timings (if any), and contains flags indicating
117device state. Mapping the BIOS can be done using the pci_map_rom()
118call, a convenience function that takes care of mapping the actual ROM,
119whether it has been shadowed into memory (typically at address 0xc0000)
120or exists on the PCI device in the ROM BAR. Note that after the ROM has
121been mapped and any necessary information has been extracted, it should
122be unmapped; on many devices, the ROM address decoder is shared with
123other BARs, so leaving it mapped could cause undesired behaviour like
124hangs or memory corruption.
125
126Managed Resources
127-----------------
128
129.. kernel-doc:: drivers/gpu/drm/drm_managed.c
130 :doc: managed resources
131
132.. kernel-doc:: drivers/gpu/drm/drm_managed.c
133 :export:
134
135.. kernel-doc:: include/drm/drm_managed.h
136 :internal:
137
138Open/Close, File Operations and IOCTLs
139======================================
140
141.. _drm_driver_fops:
142
143File Operations
144---------------
145
146.. kernel-doc:: drivers/gpu/drm/drm_file.c
147 :doc: file operations
148
149.. kernel-doc:: include/drm/drm_file.h
150 :internal:
151
152.. kernel-doc:: drivers/gpu/drm/drm_file.c
153 :export:
154
155Misc Utilities
156==============
157
158Printer
159-------
160
161.. kernel-doc:: include/drm/drm_print.h
162 :doc: print
163
164.. kernel-doc:: include/drm/drm_print.h
165 :internal:
166
167.. kernel-doc:: drivers/gpu/drm/drm_print.c
168 :export:
169
170Utilities
171---------
172
173.. kernel-doc:: include/drm/drm_util.h
174 :doc: drm utils
175
176.. kernel-doc:: include/drm/drm_util.h
177 :internal:
178
179
180Unit testing
181============
182
183KUnit
184-----
185
186KUnit (Kernel unit testing framework) provides a common framework for unit tests
187within the Linux kernel.
188
189This section covers the specifics for the DRM subsystem. For general information
190about KUnit, please refer to Documentation/dev-tools/kunit/start.rst.
191
192How to run the tests?
193~~~~~~~~~~~~~~~~~~~~~
194
195In order to facilitate running the test suite, a configuration file is present
196in ``drivers/gpu/drm/tests/.kunitconfig``. It can be used by ``kunit.py`` as
197follows:
198
199.. code-block:: bash
200
201 $ ./tools/testing/kunit/kunit.py run --kunitconfig=drivers/gpu/drm/tests \
202 --kconfig_add CONFIG_VIRTIO_UML=y \
203 --kconfig_add CONFIG_UML_PCI_OVER_VIRTIO=y
204
205.. note::
206 The configuration included in ``.kunitconfig`` should be as generic as
207 possible.
208 ``CONFIG_VIRTIO_UML`` and ``CONFIG_UML_PCI_OVER_VIRTIO`` are not
209 included in it because they are only required for User Mode Linux.
210
211
212Legacy Support Code
213===================
214
215The section very briefly covers some of the old legacy support code
216which is only used by old DRM drivers which have done a so-called
217shadow-attach to the underlying device instead of registering as a real
218driver. This also includes some of the old generic buffer management and
219command submission code. Do not use any of this in new and modern
220drivers.
221
222Legacy Suspend/Resume
223---------------------
224
225The DRM core provides some suspend/resume code, but drivers wanting full
226suspend/resume support should provide save() and restore() functions.
227These are called at suspend, hibernate, or resume time, and should
228perform any state save or restore required by your device across suspend
229or hibernate states.
230
231int (\*suspend) (struct drm_device \*, pm_message_t state); int
232(\*resume) (struct drm_device \*);
233Those are legacy suspend and resume methods which *only* work with the
234legacy shadow-attach driver registration functions. New driver should
235use the power management interface provided by their bus type (usually
236through the :c:type:`struct device_driver <device_driver>`
237dev_pm_ops) and set these methods to NULL.
238
239Legacy DMA Services
240-------------------
241
242This should cover how DMA mapping etc. is supported by the core. These
243functions are deprecated and should not be used.
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
42Driver Features
43~~~~~~~~~~~~~~~
44
45Drivers inform the DRM core about their requirements and supported
46features by setting appropriate flags in the driver_features field.
47Since those flags influence the DRM core behaviour since registration
48time, most of them must be set to registering the :c:type:`struct
49drm_driver <drm_driver>` instance.
50
51u32 driver_features;
52
53DRIVER_USE_AGP
54 Driver uses AGP interface, the DRM core will manage AGP resources.
55
56DRIVER_LEGACY
57 Denote a legacy driver using shadow attach. Don't use.
58
59DRIVER_KMS_LEGACY_CONTEXT
60 Used only by nouveau for backwards compatibility with existing userspace.
61 Don't use.
62
63DRIVER_PCI_DMA
64 Driver is capable of PCI DMA, mapping of PCI DMA buffers to
65 userspace will be enabled. Deprecated.
66
67DRIVER_SG
68 Driver can perform scatter/gather DMA, allocation and mapping of
69 scatter/gather buffers will be enabled. Deprecated.
70
71DRIVER_HAVE_DMA
72 Driver supports DMA, the userspace DMA API will be supported.
73 Deprecated.
74
75DRIVER_HAVE_IRQ; DRIVER_IRQ_SHARED
76 DRIVER_HAVE_IRQ indicates whether the driver has an IRQ handler
77 managed by the DRM Core. The core will support simple IRQ handler
78 installation when the flag is set. The installation process is
79 described in ?.
80
81 DRIVER_IRQ_SHARED indicates whether the device & handler support
82 shared IRQs (note that this is required of PCI drivers).
83
84DRIVER_GEM
85 Driver use the GEM memory manager.
86
87DRIVER_MODESET
88 Driver supports mode setting interfaces (KMS).
89
90DRIVER_PRIME
91 Driver implements DRM PRIME buffer sharing.
92
93DRIVER_RENDER
94 Driver supports dedicated render nodes.
95
96DRIVER_ATOMIC
97 Driver supports atomic properties. In this case the driver must
98 implement appropriate obj->atomic_get_property() vfuncs for any
99 modeset objects with driver specific properties.
100
101DRIVER_SYNCOBJ
102 Driver support drm sync objects.
103
104Major, Minor and Patchlevel
105~~~~~~~~~~~~~~~~~~~~~~~~~~~
106
107int major; int minor; int patchlevel;
108The DRM core identifies driver versions by a major, minor and patch
109level triplet. The information is printed to the kernel log at
110initialization time and passed to userspace through the
111DRM_IOCTL_VERSION ioctl.
112
113The major and minor numbers are also used to verify the requested driver
114API version passed to DRM_IOCTL_SET_VERSION. When the driver API
115changes between minor versions, applications can call
116DRM_IOCTL_SET_VERSION to select a specific version of the API. If the
117requested major isn't equal to the driver major, or the requested minor
118is larger than the driver minor, the DRM_IOCTL_SET_VERSION call will
119return an error. Otherwise the driver's set_version() method will be
120called with the requested version.
121
122Name, Description and Date
123~~~~~~~~~~~~~~~~~~~~~~~~~~
124
125char \*name; char \*desc; char \*date;
126The driver name is printed to the kernel log at initialization time,
127used for IRQ registration and passed to userspace through
128DRM_IOCTL_VERSION.
129
130The driver description is a purely informative string passed to
131userspace through the DRM_IOCTL_VERSION ioctl and otherwise unused by
132the kernel.
133
134The driver date, formatted as YYYYMMDD, is meant to identify the date of
135the latest modification to the driver. However, as most drivers fail to
136update it, its value is mostly useless. The DRM core prints it to the
137kernel log at initialization time and passes it to userspace through the
138DRM_IOCTL_VERSION ioctl.
139
140Device Instance and Driver Handling
141-----------------------------------
142
143.. kernel-doc:: drivers/gpu/drm/drm_drv.c
144 :doc: driver instance overview
145
146.. kernel-doc:: include/drm/drm_drv.h
147 :internal:
148
149.. kernel-doc:: drivers/gpu/drm/drm_drv.c
150 :export:
151
152Driver Load
153-----------
154
155
156IRQ Helper Library
157~~~~~~~~~~~~~~~~~~
158
159.. kernel-doc:: drivers/gpu/drm/drm_irq.c
160 :doc: irq helpers
161
162.. kernel-doc:: drivers/gpu/drm/drm_irq.c
163 :export:
164
165Memory Manager Initialization
166~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
167
168Every DRM driver requires a memory manager which must be initialized at
169load time. DRM currently contains two memory managers, the Translation
170Table Manager (TTM) and the Graphics Execution Manager (GEM). This
171document describes the use of the GEM memory manager only. See ? for
172details.
173
174Miscellaneous Device Configuration
175~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
176
177Another task that may be necessary for PCI devices during configuration
178is mapping the video BIOS. On many devices, the VBIOS describes device
179configuration, LCD panel timings (if any), and contains flags indicating
180device state. Mapping the BIOS can be done using the pci_map_rom()
181call, a convenience function that takes care of mapping the actual ROM,
182whether it has been shadowed into memory (typically at address 0xc0000)
183or exists on the PCI device in the ROM BAR. Note that after the ROM has
184been mapped and any necessary information has been extracted, it should
185be unmapped; on many devices, the ROM address decoder is shared with
186other BARs, so leaving it mapped could cause undesired behaviour like
187hangs or memory corruption.
188
189Bus-specific Device Registration and PCI Support
190------------------------------------------------
191
192A number of functions are provided to help with device registration. The
193functions deal with PCI and platform devices respectively and are only
194provided for historical reasons. These are all deprecated and shouldn't
195be used in new drivers. Besides that there's a few helpers for pci
196drivers.
197
198.. kernel-doc:: drivers/gpu/drm/drm_pci.c
199 :export:
200
201Open/Close, File Operations and IOCTLs
202======================================
203
204.. _drm_driver_fops:
205
206File Operations
207---------------
208
209.. kernel-doc:: drivers/gpu/drm/drm_file.c
210 :doc: file operations
211
212.. kernel-doc:: include/drm/drm_file.h
213 :internal:
214
215.. kernel-doc:: drivers/gpu/drm/drm_file.c
216 :export:
217
218Misc Utilities
219==============
220
221Printer
222-------
223
224.. kernel-doc:: include/drm/drm_print.h
225 :doc: print
226
227.. kernel-doc:: include/drm/drm_print.h
228 :internal:
229
230.. kernel-doc:: drivers/gpu/drm/drm_print.c
231 :export:
232
233
234Legacy Support Code
235===================
236
237The section very briefly covers some of the old legacy support code
238which is only used by old DRM drivers which have done a so-called
239shadow-attach to the underlying device instead of registering as a real
240driver. This also includes some of the old generic buffer management and
241command submission code. Do not use any of this in new and modern
242drivers.
243
244Legacy Suspend/Resume
245---------------------
246
247The DRM core provides some suspend/resume code, but drivers wanting full
248suspend/resume support should provide save() and restore() functions.
249These are called at suspend, hibernate, or resume time, and should
250perform any state save or restore required by your device across suspend
251or hibernate states.
252
253int (\*suspend) (struct drm_device \*, pm_message_t state); int
254(\*resume) (struct drm_device \*);
255Those are legacy suspend and resume methods which *only* work with the
256legacy shadow-attach driver registration functions. New driver should
257use the power management interface provided by their bus type (usually
258through the :c:type:`struct device_driver <device_driver>`
259dev_pm_ops) and set these methods to NULL.
260
261Legacy DMA Services
262-------------------
263
264This should cover how DMA mapping etc. is supported by the core. These
265functions are deprecated and should not be used.