Display

1. Composition: blends individual layers into a single frame and sends it to the display panel
2. Scaling: supports upscale and downscale of the source image to match the panel resolution
3. Color format conversion: converts colors from one color format to another (from YUV to RGB)
4. Color space conversion: converts colors from one color space to another (sRGB, P3, and BT2020)
5. Color processing: enhances the colors for better visual quality
6. Interfaces: Connects with various panels using the mobile industry processor interface display serial interface (MIPI DSI) and TV or monitor with the DisplayPort interface
7. MIPI DSI: defines the protocols between a host processor and peripheral devices that adhere to the MIPI Alliance specifications for mobile device interfaces
8. DisplayPort: serves as a digital display interface, primarily connecting video sources to display devices such as computer monitors, and can also transmit audio, USB, and other data forms

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Display Architecture

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DPU Hardware Architecture

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Display Software Architecture

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Display specifications

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Display features

1. Wayland and Weston with upstream protocol
2. Weston compositor with direct rendering manager (DRM) backend module
3. DSI interface
4. 2xDisplayPort with single stream transport (SST)

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Setup the DisplayPort

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Connect DisplayPort

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Verify DisplayPort Setup

1

Connect primary display

Connect a DisplayPort cable to the eDP0 connector.

2

Connect secondary display (optional)

For dual display, connect a second DisplayPort cable to eDP1.

3

Power on

Power on the device. Weston launches automatically during boot and displays the flower pattern.

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SSH Access

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Testing and Verification

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Run the Weston simple EGL client application

mount -o remount,rw /

. /etc/profile

export XDG_RUNTIME_DIR=/run/user/1000 && mkdir -p $XDG_RUNTIME_DIR

cd /usr/bin

export WAYLAND_DISPLAY=wayland-1 && weston-simple-egl

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Run the DRM modetest application

1. To kill the Weston client application, run the following commands in the device shell:

mount -o remount,rw /

ps -A | grep weston

824 ?        00:00:12 weston
1090 ?        00:00:00 weston-keyboard
1092 ?        00:00:01 weston-desktop-

2. To kill all Weston processes, run the following command:

systemctl stop weston.service

chmod 0777 /usr/bin/modetest

4. To view the connector IDs and modes, run the following command:

/usr/bin/modetest -M msm > /opt/drm_mode.txt

5. To verify DRM modes and connector information, pull the /opt/drm_mode.txt file locally on your host computer. Use the Secure Copy Protocol (SCP) to pull the drm_mode.txt file from the device to your host computer. For example,

scp -r root@<IP of the device>:/opt/drm_mode.txt <directory path of the host machine>

6. To fetch the connector ID, mode name and refresh rate use the relevant values from the /opt/drm_mode.txt file:

modetest -M msm -s <Connector id>:<mode name>-<refresh>

7. To start the modetest application, run the following sample command using the connector ID and the mode name retrieved from the /opt/drm_mode.txt file. For example:

/usr/bin/modetest -M msm -s 32:1920x1080-60

systemctl start weston.service

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Troubleshooting

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Check DisplayPort Status

 mount -t debugfs none /sys/kernel/debug

# Cable status
cat /sys/class/drm/card0-DP-1/status   # eDP0
cat /sys/class/drm/card0-DP-2/status   # eDP1

# Available modes (EDID)
cat /sys/class/drm/card0-DP-1/modes

# Detailed DP info
cat /sys/kernel/debug/dri/0/DP-1/dp_debug

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Resources