1 .. _vkms:
2
3 ==========================================
4 drm/vkms Virtual Kernel Modesetting
5 ==========================================
6
7 .. kernel-doc:: drivers/gpu/drm/vkms/vkms_drv.
8 :doc: vkms (Virtual Kernel Modesetting)
9
10 Setup
11 =====
12
13 The VKMS driver can be setup with the followin
14
15 To check if VKMS is loaded, run::
16
17 lsmod | grep vkms
18
19 This should list the VKMS driver. If no output
20 you need to enable and/or load the VKMS driver
21 Ensure that the VKMS driver has been set as a
22 kernel config file. Do::
23
24 make nconfig
25
26 Go to `Device Drivers> Graphics support`
27
28 Enable `Virtual KMS (EXPERIMENTAL)`
29
30 Compile and build the kernel for the changes t
31 Now, to load the driver, use::
32
33 sudo modprobe vkms
34
35 On running the lsmod command now, the VKMS dri
36 You can also observe the driver being loaded i
37
38 The VKMS driver has optional features to simul
39 which are exposed as module options. You can u
40 to see the module options for vkms::
41
42 modinfo vkms
43
44 Module options are helpful when testing, and e
45 can be done while loading vkms. For example, t
46 use::
47
48 sudo modprobe vkms enable_cursor=1
49
50 To disable the driver, use ::
51
52 sudo modprobe -r vkms
53
54 Testing With IGT
55 ================
56
57 The IGT GPU Tools is a test suite used specifi
58 development of the DRM drivers.
59 The IGT Tools can be installed from
60 `here <https://gitlab.freedesktop.org/drm/igt-
61
62 The tests need to be run without a compositor,
63 only mode. You can do this by::
64
65 sudo systemctl isolate multi-user.target
66
67 To return to graphical mode, do::
68
69 sudo systemctl isolate graphical.target
70
71 Once you are in text only mode, you can run te
72 or IGT_DEVICE variable to specify the device f
73 to test. IGT_DEVICE can also be used with the
74 tests for a specific driver::
75
76 sudo ./build/tests/<name of test> --device "
77 sudo IGT_DEVICE="sys:/sys/devices/platform/v
78 sudo IGT_DEVICE="sys:/sys/devices/platform/v
79
80 For example, to test the functionality of the
81 we can run the kms_writeback test::
82
83 sudo ./build/tests/kms_writeback --device "s
84 sudo IGT_DEVICE="sys:/sys/devices/platform/v
85 sudo IGT_DEVICE="sys:/sys/devices/platform/v
86
87 You can also run subtests if you do not want t
88
89 sudo ./build/tests/kms_flip --run-subtest ba
90 sudo IGT_DEVICE="sys:/sys/devices/platform/v
91
92 TODO
93 ====
94
95 If you want to do any of the items listed belo
96 with VKMS maintainers.
97
98 IGT better support
99 ------------------
100
101 Debugging:
102
103 - kms_plane: some test cases are failing due t
104
105 Virtual hardware (vblank-less) mode:
106
107 - VKMS already has support for vblanks simulat
108 tested with kms_flip test; in some way, we c
109 the real hardware vblank. However, we also h
110 not support vblank interrupt and completes p
111 this case, compositor developers may end up
112 hardware. It would be useful to support Virt
113 because this can help compositor developers
114 multiple scenarios.
115
116 Add Plane Features
117 ------------------
118
119 There's lots of plane features we could add su
120
121 - Add background color KMS property[Good to ge
122
123 - Scaling.
124
125 - Additional buffer formats, especially YUV fo
126 Low/high bpp RGB formats would also be inter
127
128 - Async updates (currently only possible on cu
129 cursor api).
130
131 For all of these, we also want to review the i
132 all relevant igt testcases work on vkms. They
133 project.
134
135 Runtime Configuration
136 ---------------------
137
138 We want to be able to reconfigure vkms instanc
139 module. Use/Test-cases:
140
141 - Hotplug/hotremove connectors on the fly (to
142 of compositors).
143
144 - Configure planes/crtcs/connectors (we'd need
145 them first).
146
147 - Change output configuration: Plug/unplug scr
148 the refresh rate.
149
150 The currently proposed solution is to expose v
151 configfs. All existing module options should b
152 too.
153
154 Writeback support
155 -----------------
156
157 - The writeback and CRC capture operations sha
158 boolean to ensure vblanks. Probably, when th
159 composer_enabled needs to refcounting the co
160 [Good to get started]
161
162 - Add support for cloned writeback outputs and
163 cloned output in the IGT kms_writeback.
164
165 - As a v4l device. This is useful for debuggin
166 configurations, so that developers see what'
167
168 Output Features
169 ---------------
170
171 - Variable refresh rate/freesync support. This
172 sharing support, so that we can use vgem fen
173 testing. Also needs support to specify the E
174
175 - Add support for link status, so that composi
176 fallbacks when e.g. a Display Port link goes
177
178 CRC API Improvements
179 --------------------
180
181 - Optimize CRC computation ``compute_crc()`` a
182
183 Atomic Check using eBPF
184 -----------------------
185
186 Atomic drivers have lots of restrictions which
187 any explicit form through e.g. possible proper
188 inquiry about these limits through the atomic
189 TEST_ONLY flag. Trying to add configurable cod
190 compositors to be tested against them, would b
191 we could add support for eBPF to validate any
192 implement a library of different restrictions.
193
194 This needs a bunch of features (plane composit
195 enabled already to make sense.
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