Boot issues with mainline kernel on Huawei Nexus 6P angler (MSM8994)

[Petr Vorel <petr.vorel@gmail.com>]

Hi,

I'm trying to test mainline kernel on Huawei Nexus 6P angler (MSM8994).
In the middle of boot (after "Serial: AMBA PL011 UART driver") phone got reset
Here is log from UART:

[119100] cmdline=console=ttyAMA0 console=ttyAMA1 console=ttyAMA2 console=ttyMSM0 console=ttyMSM1 console=ttyMSM2 keep_bootcon earlycon debug ignore_loglevel PMOS_NO_OUTPUT_REDIRECT
=> PMOS_NO_OUTPUT_REDIRECT is postmarketOS specific, I tested various console setup
...
[119510] boardid:8026
[119520] booting linux @ 0x80000, ramdisk @ 0x2700000 (1314539), tags/device tree @ 0x2500000
[119530] Jumping to kernel via monitor
[    0.000000] Booting Linux on physical CPU 0x0000000000 [0x410fd032]
[    0.000000] Linux version 5.12.0-rc2 (pmos@dell5510) (aarch64-alpine-linux-musl-gcc (Alpine 10.2.1_git20210318) 10.2.1 20210318, GNU ld (GNU Binutils) 2.35.2) #1 SMP PREEMPT Thu Mar 25 14:39:46 UTC 2021
[    0.000000] Machine model: Huawei Nexus 6P
[    0.000000] printk: debug: skip boot console de-registration.
[    0.000000] printk: debug: ignoring loglevel setting.
[    0.000000] efi: UEFI not found.
[    0.000000] [Firmware Bug]: Kernel image misaligned at boot, please fix your bootloader!
[    0.000000] earlycon: msm_serial_dm0 at MMIO 0x00000000f991e000 (options '115200n8')
[    0.000000] printk: bootconsole [msm_serial_dm0] enabled
...
[    0.244277] cpuidle: using governor menu
[    0.252555] hw-breakpoint: found 6 breakpoint and 4 watchpoint registers.
[    0.255958] ASID allocator initialised with 32768 entries
[    0.264414] Serial: AMBA PL011 UART driver
=> phone resets, continue first stage bootloader, Little Kernel and downstream kernel (LineageOS)
D -     15494 - pm_driver_init, Delta
B -    622413 - cpr_init, Start

I'm using original Little kernel bootloader, arm64 defconfig and
msm8994-angler-rev-101.dtb (obviously).

I tried various things:
* test various kernel versions current qcom/for-next, various v5.x versions,
  v4.10 (which brought MSM8994 support)
* keep_bootcon earlycon ignore_loglevel debug kernel parameters
* use various consoles (e.g. ttyMSM[0-2] and downstream ttyHSL0, ttyAMA0 or
  no console defined at all)
* original AOSP boot.img and boot.img from postmarketOS project (with updated
  kernel with abootimg
* although it should not be caused by missing SELinux (AOSP/postmarketOS
  require SELinux enabled), I also tested with SELinux enabled
  (CONFIG_DEFAULT_SECURITY_SELINUX=y, CONFIG_LSM="selinux", ...)

It behaves the same on all. I even tried to remove serial config from DTS
(serial@f991e000 and alias serial0 = &blsp1_uart2), which lead only to
(obviously) disabled UART, but phone still resets.
Unplugging UART didn't help either.

I looked into /sys/fs/pstore/ (rooted phone), but /sys/fs/pstore/console-ramoops
has content of rebooted kernel (LineageOS one), not the mainline.

I have no idea what could be wrong. Whether UART dts definition or something else.
I suppose the problem is with dts, not with code itself.

Any idea what to look for?  I can provide more logs, if needed.

Kind regards,
Petr