QCS6490

Debug the high-definition multimedia interface (HDMI) display

Connect to the target through SSH and run target commands from the root shell. For instructions, see Sign in using SSH.

The QCS6490 HDMI path routes DSI0 through the Lontium LT9611UXC DSI-to-HDMI bridge to HDMI-A-1. Step 4 checks the DSI pixel clock that feeds this bridge, so it verifies the source signal for HDMI. Step 5 checks LT9611UXC bridge messages, and the optional firmware step applies to this bridge.

Figure: QCS6490 HDMI cable connection

1. Identify the connector

Run the following command:

modetest -M msm -c

This lists the HDMI connector, its DRM ID, and the connection state.

Reference output

34      33      connected       HDMI-A-1        480x270         13      33

2. Check connector status and modes

Run the following command:

cat /sys/class/drm/card0-HDMI-A-1/status

This reports whether HDMI is connected. The expected result is connected.Run the following command:

cat /sys/class/drm/card0-HDMI-A-1/modes

This lists the modes reported by the connected monitor.If HDMI is disconnected or reports no modes, check the cable, monitor power, and selected HDMI input. DRM object IDs and card numbers can vary by build.

3. Check the active DRM state

If debugfs is not mounted, run the following command:

mount -t debugfs none /sys/kernel/debug

This makes DRM state and interface debug data available.Run the following command:

modetest -M msm -c -p

This shows the HDMI encoder, CRTC, mode, and plane.

Reference output

CRTCs:
70      78      (0,0)   (1920x1080)
  #0 1920x1080 60.00

Run the following command:

cat /sys/kernel/debug/dri/0/state

This shows the kernel DRM connector, encoder, CRTC, and plane state.For HDMI-A-1, confirm one active display pipeline:

status: connected
A nonzero CRTC ID
active=yes for that CRTC
A plane whose crtc field matches that CRTC ID

Restore Weston after testing a display mode.To test a different mode, follow Run DRM modetest, then Relaunch Weston before returning to Weston tests.

4. Check interface signals

Run the following command:

cat /sys/kernel/debug/clk/disp_cc_mdss_pclk*/clk_rate

This prints the available DSI pixel-clock rates used by the HDMI bridge in Hz.

Reference output

148500000

Compare the rate with the active CRTC pixel clock, which modetest reports in kHz. If the clock path is absent, continue with the DRM state and kernel log checks.

5. Check current-boot kernel messages and live display events

Run the following command:

journalctl -k -b --no-pager -o short-monotonic | grep -Ei 'lt9611|lontium|hdmi|edid|dsi|dpu|drm'

This shows bridge, EDID, DSI, and DRM messages from the current boot only. If it returns no lines, capture live data while reproducing the issue.

Reference output

[   16.611725] lt9611uxc 0-002b: LT9611 revision: 0x17.04.93
[   18.207709] msm_dpu ae01000.display-controller: bound ae94000.dsi
[   18.299943] [drm] Initialized msm 1.13.0 for ae01000.display-controller

To capture display events while reproducing the issue, run the following command:

journalctl -f

This follows new Weston and kernel messages. Run it without -k so the output includes compositor connector changes and output enablement. Reproduce the issue, then press Ctrl+C.Look for connector-state changes, EDID or mode detection, output enablement, and driver errors. Compare the relevant messages with the connector status and active DRM state.EDID or I2C errors point to the monitor, cable, or bridge.

6. Interpret the result

Result	Likely area	Next action
`disconnected` after reconnecting, or no new display message and no status change	Cable, monitor input, bridge, or HPD path	Reseat the cable, select the HDMI input, and recheck connector status.
Connected with no modes or EDID/I2C errors	Monitor, cable, or bridge	Check the cable and monitor, then inspect bridge messages.
Mode reported, but the connector, CRTC, and plane do not form one active pipeline	DRM or compositor	Check the active DRM state and Weston status.
Active CRTC but blank screen	Bridge or Weston	Compare the DSI clock, bridge log, and Wayland output.

Verify the Weston service before checking the output layout.Run the following command:

systemctl is-active weston

The expected result is active. If the service is not active, Relaunch Weston before continuing.

7. Check Weston and the output layout

Run the following command:

journalctl -b -u weston -n 40 --no-pager

This shows the latest Weston messages from the current boot.Run the following command if Weston is active but the display is blank:

find /run/user/<weston-uid> -maxdepth 1 -type s -name 'wayland-*' -printf '%f\n'

This lists the available Wayland socket names.Run the following command after replacing the placeholders:

runuser -u weston -- env XDG_RUNTIME_DIR=/run/user/<weston-uid> WAYLAND_DISPLAY=<socket-name> wayland-info

Compare the Weston output with DRM state.This prints Weston output information. Find the selected display output and compare it with the DRM connector and CRTC state. If Weston is inactive, Relaunch Weston before continuing.

Optional: Update Lontium firmware

Update firmware only after the connection, mode, and bridge checks fail. Download the latest LT9611UXC firmware image from the Lontium website. Open the Qualcomm section and select the firmware image for this board. LT9611UXC_DSI_PortA_HDCP_Disable_V5.0.21.bin is an example filename; use the latest available image when copying it to the target.Run the following command on the target:

mount -o rw,remount /usr

This makes the firmware location writable.Run the following command on the host:

scp <firmware.bin> root@<device-ip>:/lib/firmware/lt9611uxc_fw.bin

Replace <firmware.bin> with the downloaded filename. This copies the firmware image to the target.Run the following command on the target:

sync

This flushes the copied firmware to storage.Run the following command on the target:

echo 0 > /sys/bus/i2c/devices/0-002b/lt9611uxc_firmware

This starts the firmware update.Run the following command on the target:

journalctl -k -b --no-pager -o short-monotonic | grep -i lt9611

This shows the firmware-update result from the current boot. Wait for at least three minutes, confirm Firmware updates successfully, then hard-reboot the device.

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Debug the high-definition multimedia interface (HDMI) display

1. Identify the connector

2. Check connector status and modes

3. Check the active DRM state

4. Check interface signals

5. Check current-boot kernel messages and live display events

6. Interpret the result

7. Check Weston and the output layout

Optional: Update Lontium firmware