1========================
2Display Core Debug tools
3========================
4
5DC Visual Confirmation
6======================
7
8Display core provides a feature named visual confirmation, which is a set of
9bars added at the scanout time by the driver to convey some specific
10information. In general, you can enable this debug option by using::
11
12  echo <N> > /sys/kernel/debug/dri/0/amdgpu_dm_visual_confirm
13
14Where `N` is an integer number for some specific scenarios that the developer
15wants to enable, you will see some of these debug cases in the following
16subsection.
17
18Multiple Planes Debug
19---------------------
20
21If you want to enable or debug multiple planes in a specific user-space
22application, you can leverage a debug feature named visual confirm. For
23enabling it, you will need::
24
25  echo 1 > /sys/kernel/debug/dri/0/amdgpu_dm_visual_confirm
26
27You need to reload your GUI to see the visual confirmation. When the plane
28configuration changes or a full update occurs there will be a colored bar at
29the bottom of each hardware plane being drawn on the screen.
30
31* The color indicates the format - For example, red is AR24 and green is NV12
32* The height of the bar indicates the index of the plane
33* Pipe split can be observed if there are two bars with a difference in height
34  covering the same plane
35
36Consider the video playback case in which a video is played in a specific
37plane, and the desktop is drawn in another plane. The video plane should
38feature one or two green bars at the bottom of the video depending on pipe
39split configuration.
40
41* There should **not** be any visual corruption
42* There should **not** be any underflow or screen flashes
43* There should **not** be any black screens
44* There should **not** be any cursor corruption
45* Multiple plane **may** be briefly disabled during window transitions or
46  resizing but should come back after the action has finished
47
48Pipe Split Debug
49----------------
50
51Sometimes we need to debug if DCN is splitting pipes correctly, and visual
52confirmation is also handy for this case. Similar to the MPO case, you can use
53the below command to enable visual confirmation::
54
55  echo 1 > /sys/kernel/debug/dri/0/amdgpu_dm_visual_confirm
56
57In this case, if you have a pipe split, you will see one small red bar at the
58bottom of the display covering the entire display width and another bar
59covering the second pipe. In other words, you will see a bit high bar in the
60second pipe.
61
62DTN Debug
63=========
64
65DC (DCN) provides an extensive log that dumps multiple details from our
66hardware configuration. Via debugfs, you can capture those status values by
67using Display Test Next (DTN) log, which can be captured via debugfs by using::
68
69  cat /sys/kernel/debug/dri/0/amdgpu_dm_dtn_log
70
71Since this log is updated accordingly with DCN status, you can also follow the
72change in real-time by using something like::
73
74  sudo watch -d cat /sys/kernel/debug/dri/0/amdgpu_dm_dtn_log
75
76When reporting a bug related to DC, consider attaching this log before and
77after you reproduce the bug.
78