Dietpi: ODROID 3.5" LCD shield backlight not turning on with the current kernel

[Kreeblah]

Creating a bug report/issue:

Required Information:

• DietPi version | v6.17.12
• Distro version | stretch
• Kernel version | Linux DietPi 3.16.57+ #1 SMP PREEMPT Sun Aug 19 15:27:56 CEST 2018 aarch64 GNU/Linux
• SBC device | Odroid C2 (aarch64)
• Power supply used | https://ameridroid.com/products/5v-2a-power-supply
• SDcard used | https://ameridroid.com/products/emmc-module-c2-linux-red-box

Additional Information (if applicable):

• Software title | dietpi-cloudshell
• Was the software title installed freshly or updated/migrated? Freshly installed
• Can this issue be replicated on a fresh installation of DietPi? Yes
• Bugreport ID: dd8eaf40-8f9b-4377-8bbf-210dde45ce63

Steps to reproduce:

1. Perform a fresh install of DietPi
2. Configure DietPi to use the odroid-lcd35 screen via the display options in dietpi-config
3. Install dietpi-cloudshell
4. Configure dietpi-cloudshell to use tty1
5. Run dietpi-autostart to run dietpi-cloudshell at boot
6. Reboot

Expected behaviour:

• The LCD should light up and display the scenes from dietpi-cloudshell

Actual behaviour:

• The LCD doesn't light up.

Extra details:

• At some point, the paths to echo things to changed. This is reflected in the ODROID documentation under how to enable the display on 18.04 at https://wiki.odroid.com/accessory/display/3.5inch_lcd_shield/3.5inch_lcd_shield
• I was able to resolve this by editing /etc/systemd/system/odroid-lcd35.service and removing the "/platform" strings in the paths where things get echoed to since that's the difference between the old and new paths.

[MichaIng]

@Kreeblah
Thanks for your report and research+solution. Indeed we currently add the path with platform/ inside: https://github.com/Fourdee/DietPi/blob/dev/dietpi/func/dietpi-set_hardware#L850-L869

They mention this changed with Ubuntu 18.04 but I guess it's about the kernel version. We either need to verify, that on all our images the required kernel will be installed (at least with first run update), or somehow add a file check to the service to automatically choose the right files.

€:

If you're using Ubuntu 18.04 on C2, enter the following commands instead.

Ah wait, does this mean it changed on C2 only, not on C1? 🤔

[MichaIng]

@Kreeblah @Fourdee
Added PR for auto detection: https://github.com/Fourdee/DietPi/pull/2265
Theoretically it can still fail, when APT update to the new kernel version is done. Then user would need to re-enable the LCD without an LCD (e.g. after reboot). Not sure if we can assume that on Jessie the config files remain the same and on Stretch, with next dietpi-update, APT updates the kernel accordingly?

Then we could use config files based on G_DISTRO and simply update the service file for all C1/2 Stretch systems on patch_file.

[Fourdee]

C2

root@DietPi:~# find /sys -name pwm*
/sys/bus/platform/devices/pwm
/sys/bus/platform/devices/pwm-ctrl
/sys/devices/pwm
/sys/devices/pwm-ctrl

root@DietPi:~# ls -lha /sys/devices/pwm-ctrl/
driver/    enable0    modalias   subsystem/
duty0      freq0      power/     uevent

🈯️

root@DietPi:~# [[ -e '/sys/devices/pwm-ctrl/enable0' ]] && fp_control='/sys/devices/pwm-ctrl'
root@DietPi:~# echo $fp_control
/sys/devices/pwm-ctrl

[MichaIng]

@Fourdee
Do you have a chance to check on Jessie?

[Fourdee]

@MichaIng

1 sec, fails on install due to not modprobe, dir not available.

[Fourdee]

Testing https://github.com/Fourdee/DietPi/commit/5c1e0f88e0c4183c5be4130cd8ce245304137da5:

• 🈯️ C2 Stretch
• C2 Jessie

[MichaIng]

@Fourdee
Ah makes sense. Is anyway food to use modprobe where possible, so we can start service directly skip reboot requirement as well?

[Fourdee]

@MichaIng

so we can start service directly skip reboot requirement as well?

In theory yep 👍

[Fourdee]

Jessie working fine 👍

root@DietPi:~# cat /etc/systemd/system/odroid-lcd35.service
[Unit]
Description=Odroid LCD 3.5

[Path]
PathExists=/dev/fb2

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/bin/bash -c 'echo 500000 > /sys/devices/platform/pwm-ctrl/freq0'
ExecStart=/bin/bash -c 'echo 1 > /sys/devices/platform/pwm-ctrl/enable0'
ExecStart=/bin/bash -c 'echo 1023 > /sys/devices/platform/pwm-ctrl/duty0'
ExecStart=/usr/bin/setterm -blank 0 -powersave off
ExecStart=/bin/con2fbmap 1 2
StandardOutput=tty

[Install]
WantedBy=multi-user.target
root@DietPi:~# ls -lha /sys/devices/platform/pwm-ctrl/freq0
-rwxrwxrwx 1 root root 4.0K Nov 20 20:11 /sys/devices/platform/pwm-ctrl/freq0

Completed. Thanks @MichaIng