2021–10–21: Pinephone Pro – levinboot payload selection

I've extended Levinboot with support for chosing which payload to boot based on status of volume keys. Levinboot will also report which payload was booted using LED color. Ordering of payloads is based on physical location of volume keys, thus:

Just power key press: payload A, red LED (on my setup this is the kernel version that is actively under development and possibly broken/may fail to boot)
Power key + volume down: payload B, blue LED (second testing kernel, less debug output)
Power key + volume down: payload C, green LED (failsafe, known to work kernel)

Here's a little demo:

With this setup it's easy to quickly try new kernel changes without any worry, and without having to swap uSD cards or open the phone ever again. The feeback cycle from code change to a booted kernel can be as fast as 10s, which makes for very pleasant development experience.

5.15 kernel fixed

I've managed to identify the cause for boot hangs on 5.15 kernel. The hang happens in of_platform_default_populate when processing the newly added debug@fe610000 (arm coresight) DT nodes (specifically the ones for the big ARM cores).

Precise reason is unknown to me, but I can live without the coresight support, so I commented those nodes out, and the 5.15 kernel now boots fine.

This allowed me to start playing with camera sensors support. I tried to add as much necessary support for the cameras as possible, and found a few issues in the process:

IMX258 device tree bindings had some documented properties that were nevertheless not implemented by the driver. I've added support for those to the driver.
IMX258 driver is made to only work with 19.2 Mhz clock which the rk3399 can't provide precisely. So I've made the driver accept somewhat unprecise frequency that rk3399 can generate.
Making rk3399 generate the proper frequency on the CIF_OUT pin required changing parent of the cif_out clock to something else than the default 24 MHz oscillator. I had to patch the rk3399 driver to export the cif_out_src clock to allow configuring the parent via assigned-clock-parents DT property.

I've pushed my changes to my kernel tree to various branches. I've added DT changes that should match the hardware, but for some reason cameras don't work yet and will need more debugging.

I've also found out that SD card power supply was wrongly defined in the DT. Interestingly a lot of regulators in the phone are enabled automatically by chaining output of one regulator to the enable pin of the dependent regulator. This was the case with SD card regulator, too.