Merge tag 'perf-urgent-2022-06-05' of git://git.kernel.org/pub/scm/linux/kernel/git...
[linux-block.git] / Documentation / gpu / vkms.rst
CommitLineData
ad9ff96f
HM
1.. _vkms:
2
3==========================================
4 drm/vkms Virtual Kernel Modesetting
5==========================================
6
7.. kernel-doc:: drivers/gpu/drm/vkms/vkms_drv.c
8 :doc: vkms (Virtual Kernel Modesetting)
9
63ade104
SP
10Setup
11=====
12
13The VKMS driver can be setup with the following steps:
14
15To check if VKMS is loaded, run::
16
17 lsmod | grep vkms
18
19This should list the VKMS driver. If no output is obtained, then
20you need to enable and/or load the VKMS driver.
21Ensure that the VKMS driver has been set as a loadable module in your
22kernel config file. Do::
23
24 make nconfig
25
26 Go to `Device Drivers> Graphics support`
27
28 Enable `Virtual KMS (EXPERIMENTAL)`
29
30Compile and build the kernel for the changes to get reflected.
31Now, to load the driver, use::
32
33 sudo modprobe vkms
34
35On running the lsmod command now, the VKMS driver will appear listed.
36You can also observe the driver being loaded in the dmesg logs.
37
af20724c
SP
38The VKMS driver has optional features to simulate different kinds of hardware,
39which are exposed as module options. You can use the `modinfo` command
40to see the module options for vkms::
41
42 modinfo vkms
43
44Module options are helpful when testing, and enabling modules
45can be done while loading vkms. For example, to load vkms with cursor enabled,
46use::
47
48 sudo modprobe vkms enable_cursor=1
49
63ade104
SP
50To disable the driver, use ::
51
52 sudo modprobe -r vkms
53
54Testing With IGT
55================
56
57The IGT GPU Tools is a test suite used specifically for debugging and
58development of the DRM drivers.
59The IGT Tools can be installed from
60`here <https://gitlab.freedesktop.org/drm/igt-gpu-tools>`_ .
61
62The tests need to be run without a compositor, so you need to switch to text
63only mode. You can do this by::
64
65 sudo systemctl isolate multi-user.target
66
67To return to graphical mode, do::
68
69 sudo systemctl isolate graphical.target
70
71Once you are in text only mode, you can run tests using the --device switch
72or IGT_DEVICE variable to specify the device filter for the driver we want
73to test. IGT_DEVICE can also be used with the run-test.sh script to run the
74tests for a specific driver::
75
76 sudo ./build/tests/<name of test> --device "sys:/sys/devices/platform/vkms"
77 sudo IGT_DEVICE="sys:/sys/devices/platform/vkms" ./build/tests/<name of test>
78 sudo IGT_DEVICE="sys:/sys/devices/platform/vkms" ./scripts/run-tests.sh -t <name of test>
79
80For example, to test the functionality of the writeback library,
81we can run the kms_writeback test::
82
83 sudo ./build/tests/kms_writeback --device "sys:/sys/devices/platform/vkms"
84 sudo IGT_DEVICE="sys:/sys/devices/platform/vkms" ./build/tests/kms_writeback
85 sudo IGT_DEVICE="sys:/sys/devices/platform/vkms" ./scripts/run-tests.sh -t kms_writeback
86
87You can also run subtests if you do not want to run the entire test::
88
89 sudo ./build/tests/kms_flip --run-subtest basic-plain-flip --device "sys:/sys/devices/platform/vkms"
90 sudo IGT_DEVICE="sys:/sys/devices/platform/vkms" ./build/tests/kms_flip --run-subtest basic-plain-flip
91
ad9ff96f
HM
92TODO
93====
94
5a388432
MW
95If you want to do any of the items listed below, please share your interest
96with VKMS maintainers.
d717c6df 97
5a388432
MW
98IGT better support
99------------------
d717c6df 100
fb786a48
MW
101Debugging:
102
103- kms_plane: some test cases are failing due to timeout on capturing CRC;
104
105- kms_flip: when running test cases in sequence, some successful individual
106 test cases are failing randomly; when individually, some successful test
107 cases display in the log the following error::
108
109 [drm:vkms_prepare_fb [vkms]] ERROR vmap failed: -4
110
111Virtual hardware (vblank-less) mode:
d717c6df 112
5a388432
MW
113- VKMS already has support for vblanks simulated via hrtimers, which can be
114 tested with kms_flip test; in some way, we can say that VKMS already mimics
115 the real hardware vblank. However, we also have virtual hardware that does
116 not support vblank interrupt and completes page_flip events right away; in
117 this case, compositor developers may end up creating a busy loop on virtual
118 hardware. It would be useful to support Virtual Hardware behavior in VKMS
119 because this can help compositor developers to test their features in
120 multiple scenarios.
d717c6df
DV
121
122Add Plane Features
123------------------
124
125There's lots of plane features we could add support for:
126
fb786a48
MW
127- Clearing primary plane: clear primary plane before plane composition (at the
128 start) for correctness of pixel blend ops. It also guarantees alpha channel
129 is cleared in the target buffer for stable crc. [Good to get started]
130
131- ARGB format on primary plane: blend the primary plane into background with
132 translucent alpha.
133
134- Support when the primary plane isn't exactly matching the output size: blend
135 the primary plane into the black background.
d717c6df
DV
136
137- Full alpha blending on all planes.
138
139- Rotation, scaling.
140
141- Additional buffer formats, especially YUV formats for video like NV12.
142 Low/high bpp RGB formats would also be interesting.
143
5a388432
MW
144- Async updates (currently only possible on cursor plane using the legacy
145 cursor api).
146
147For all of these, we also want to review the igt test coverage and make sure
fb786a48
MW
148all relevant igt testcases work on vkms. They are good options for internship
149project.
5a388432
MW
150
151Runtime Configuration
152---------------------
153
154We want to be able to reconfigure vkms instance without having to reload the
155module. Use/Test-cases:
156
157- Hotplug/hotremove connectors on the fly (to be able to test DP MST handling
158 of compositors).
159
160- Configure planes/crtcs/connectors (we'd need some code to have more than 1 of
161 them first).
162
163- Change output configuration: Plug/unplug screens, change EDID, allow changing
164 the refresh rate.
165
166The currently proposed solution is to expose vkms configuration through
fb786a48 167configfs. All existing module options should be supported through configfs
5a388432 168too.
d717c6df
DV
169
170Writeback support
171-----------------
172
5a388432
MW
173- The writeback and CRC capture operations share the use of composer_enabled
174 boolean to ensure vblanks. Probably, when these operations work together,
175 composer_enabled needs to refcounting the composer state to proper work.
fb786a48 176 [Good to get started]
d717c6df 177
5a388432
MW
178- Add support for cloned writeback outputs and related test cases using a
179 cloned output in the IGT kms_writeback.
d717c6df
DV
180
181- As a v4l device. This is useful for debugging compositors on special vkms
182 configurations, so that developers see what's really going on.
183
d717c6df
DV
184Output Features
185---------------
186
187- Variable refresh rate/freesync support. This probably needs prime buffer
188 sharing support, so that we can use vgem fences to simulate rendering in
189 testing. Also needs support to specify the EDID.
190
191- Add support for link status, so that compositors can validate their runtime
192 fallbacks when e.g. a Display Port link goes bad.
193
5a388432
MW
194CRC API Improvements
195--------------------
196
197- Optimize CRC computation ``compute_crc()`` and plane blending ``blend()``
d717c6df
DV
198
199Atomic Check using eBPF
200-----------------------
201
202Atomic drivers have lots of restrictions which are not exposed to userspace in
203any explicit form through e.g. possible property values. Userspace can only
204inquiry about these limits through the atomic IOCTL, possibly using the
205TEST_ONLY flag. Trying to add configurable code for all these limits, to allow
206compositors to be tested against them, would be rather futile exercise. Instead
207we could add support for eBPF to validate any kind of atomic state, and
208implement a library of different restrictions.
209
210This needs a bunch of features (plane compositing, multiple outputs, ...)
211enabled already to make sense.