Lenovo Tab 4 8 (lenovo-tb8504f)

Contributors

 * Angus-g

Unlocking
In developer options the allow oem unlock toggle may be unexpectedly disabled. In this case, try a software update to confirm latest (final) version, similar to tb-8504f_s001019_190909_row. The fastboot key combo is volume down + power. No device-specific information (e.g., bootloader version) is presented on the fastboot splash screen. shows some basic details. The standard unlock command  gives a warning and shows the correct command.

Installation
Install TWRP (3.2.3 and 3.3.1 are available). Format the System partition to prepare for the postmarketOS image. Either install from a recovery zip directly in TWRP, or use  as usual.

Note: install from a recovery zip using sdcard or via sideload fail with the  splash screen.

Status
Using the LineageOS kernel (which is derived from Lenovo's open-sourced kernel), we can boot to a graphical display with USB networking. If  is not set, it seems that there are a lot of errors regarding charging when connected via USB, and the boot doesn't get through to init. The touchscreen is detected, but the driver gets disabled in libinput due to a kernel bug.

Chipset
The chipset appears to be APQ8017, with an Adreno 300-series GPU. It seems to be very similar (at the devicetree level) to MSM8917. Neither of these currently have a mainline kernel effort. Wikipedia suggests the Snapdragon 425 MSM8917 is software-compatible with MSM8937.

The values are estimated strictly from software, not hardware, results (fastboot, adb, or twrp-3.3.1-1-TB8504 [unified 8504f/x)], using the commands given below.

chipset details (software-derived)

sample commands (software-derived)

CPU Tuning
According to  (cpufrequtils package), the chipset does indeed have a tiny frequency range, 960MHz - 1.4GHz. Benchmarks show trivial differences in performance between the available frequency governors (default is performance), and all result in thermal throttling (frequency limiting).

Battery
Charging works, monitor via

Sensors
Output of hwtest output

hwtest output (kleintux 20221119)

Output of  (lm-sensors package): sensors output

For reference, output of sensorssandbox (v1.8, f-droid): sensorssandbox results

Photos

 * Screenshot-tb8504f-xfce4-htop-about.png