U-Boot for the LG X3 T30 device family

DISCLAMER! Moving your LG P880 or P895 to use U-Boot assumes replacement of the vendor LG bootloader. Vendor android firmwares will no longer be able to run on the device. This replacement IS reversible if you have backups.

Quick Start

  • Build U-Boot

  • Process U-Boot

  • Flashing U-Boot into the eMMC

  • Boot

  • Self Upgrading

Build U-Boot

Device support is implemented by applying config fragment to a generic board defconfig. Valid fragments are p880.config and p895.config.

$ export CROSS_COMPILE=arm-none-eabi-
$ make x3_t30_defconfig p895.config # For LG Optimus Vu
$ make

After the build succeeds, you will obtain the final u-boot-dtb-tegra.bin image, ready for further processing.

Process U-Boot

DISCLAMER! All questions related to the re-crypt work should be asked in re-crypt repo issues. NOT HERE!

re-crypt is a tool that processes the u-boot-dtb-tegra.bin binary into form usable by device. This process is required only on the first installation or to recover the device in case of a failed update.

$ git clone https://gitlab.com/grate-driver/re-crypt.git
$ cd re-crypt # place your u-boot-dtb-tegra.bin here
$ ./re-crypt.py --dev p895 --split # or --dev p880

The script will produce bct.img and ebt.img ready to flash.

Flashing U-Boot into the eMMC

DISCLAMER! All questions related to fusee-tools should be asked in the proper place. NOT HERE! Flashing U-Boot will erase all eMMC, so make a backup before!

Permanent installation can be performed by pre-loading just built U-Boot into RAM. Bct and bootloader will end up in boot0 and boot1 partitions of eMMC.

You have to clone and prepare fusee-tools from here: https://gitlab.com/grate-driver/fusee-tools according to fusee-tools README to continue.

Bootloader preloading is performed to device in APX/RCM mode connected to host PC. This mode can be entered by holding power and both buttons on turned off phone connected to the host PC. Host PC should detect APX USB device in lsusb.

U-Boot pre-loaded into RAM acts the same as when it was booted “cold”. Currently U-Boot supports bootmenu entry fastboot, which allows to write a processed copy of U-Boot permanently into eMMC. This is how U-Boot can be preloaded using fusee-tools:

$ ./run_bootloader.sh -s T30 -t ./bct/p895.bct --b u-boot-dtb-tegra.bin # or p880.bct

While pre-loading U-Boot, hold the volume down button which will trigger the bootmenu. There, select fastboot using the volume and power buttons. After, on host PC, do:

$ fastboot flash 0.1 bct.img
$ fastboot flash 0.2 ebt.img
$ fastboot reboot

Device will reboot.

Boot

To boot Linux, U-Boot will look for an extlinux.conf on eMMC. Additionally, if the Volume Down button is pressed while booting, the device will enter bootmenu. Bootmenu contains entries to mount eMMC as mass storage, fastboot, reboot, reboot RCM, poweroff, enter U-Boot console and update bootloader (check the next chapter).

Flashing bct.img and ebt.img eliminates vendor restrictions on eMMC and allows the user to use/partition it in any way the user desires.

Self Upgrading

Place your u-boot-dtb-tegra.bin on the first partition of the eMMC or MicroSD card if it is supported (using ability of u-boot to mount it). Enter bootmenu, choose update bootloader option with Power button and U-Boot should update itself. Once the process is completed, U-Boot will ask to press any button to reboot.