LG K40 (lg-mmh4x)

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LG K40
LG K40 running postmarketOS with Xfce4
LG K40 running postmarketOS with Xfce4
Manufacturer LG
Name K40
Codename lg-mmh4x
Released 2019
Category testing
Original software Android 8.1
postmarketOS kernel 4.9.190
Hardware
Chipset MediaTek MT6765
CPU Octa-core 2 GHz Cortex-A53
GPU PowerVR Rogue GE8320
Display 720x1440 IPS
Storage 16 or 32 GB
Memory 2 GB
Architecture armv7
Unixbench Whet/Dhry score 3140.0
Features
USB Networking
Works
Flashing
Partial
Touchscreen
Works
Display
Works
WiFi
FDE
Broken
Mainline
Broken
Battery
Broken
3D Acceleration
Broken
Audio
Bluetooth
Broken
Camera
Broken
GPS
Mobile data
SMS
Calls
USB OTG
Works
NFC
Sensors
Accelerometer
Magnetometer
Ambient Light
Proximity
Hall Effect
Unavailable
Barometer
Power Sensor
Misc
Keyboard
Unavailable
Touchpad
Unavailable
USB-A
Unavailable
HDMI/DP
Unavailable
Ir TX
Unavailable
TrustZone
FOSS bootloader
Broken



Contributors

  • BenTheTechGuy

Users owning this device


How to enter flash mode

The LG K40 doesn't have a useful recovery mode (it's just a factory reset button), and fastboot doesn't exist at all on the device; the only possible mode is Download Mode, but that requires a signed image to flash.

Luckily, there's a tool called mtkclient that makes use of vulnerabilities in the MediaTek SoC itself, and that can be used to unlock the bootloader and flash images. It's also packaged as mtkclient on some distributions (Alpine, AUR, soon Debian/Ubuntu).

In the below examples, the command mtk is used, but if you installed from source, you'll need to run python mtk inside the repo.

To enter into a mode that mtkclient can be used in, follow these steps:

  1. Power off the device.
  2. Run an mtkclient command, like mtk printgpt.
  3. While mtkclient waits for the device, hold Volume Up and plug it into the computer.
  4. mtkclient should output a lot of text at this point. The button can be released.
  5. As long as mtkclient did its job properly, the command will succeed. Now, other commands can be run with mtkclient.

Unlocking the bootloader

  1. Enable developer options, and OEM Unlocking from there.
  2. Follow the steps in #How to enter flash mode.
  3. Erase metadata, userdata, and md_udc:
    mtk e metadata,userdata,md_udc
    Note: If metadata or md_udc don't exist, just remove them from the command.
  4. Unlock the bootloader:
    mtk da seccfg unlock
  5. Reset mtkclient:
    mtk reset
  6. The bootloader should now be unlocked. From here, the device can be unplugged and powered on to go through setup.

Installation

Since recovery or fastboot can't be used, the kernel and rootfs must be flashed manually with mtkclient. First, find out which slot is active, A or B. Normally this would be done with fastboot, but that cannot be accessed, so adb must be used.

adb shell getprop ro.boot.slot_suffix # will return either _a or _b, current active slot

pmbootstrap init # DRM is not supported yet, so Xfce4 is the best graphical option for now
pmbootstrap install # can also install to an SD card and skip flashing to userdata later
pmbootstrap export # symlink kernel and rootfs to /tmp for easy manual flashing

mtk w boot_a /tmp/postmarketOS-export/boot.img # flash kernel to boot_a or boot_b depending on active slot
mtk w userdata /tmp/postmarketOS-export/lg-mmh4x.img # flash rootfs to userdata partition

mtk reset
# unplug the device, turn it back on, and enjoy postmarketOS :)

See also