msm8996: qcom-qmp: apq8096-db820c fails to boot, reset back to fastboot and locks up

[Paolo Pisati <p.pisati@gmail.com>]

From time to time, my apq8096-db820c fails to boot to userspace, reset back to
fastboot and locks up: to easily reproduce the issue, i'm boot looping using a
cron job with a 1 min reboot entry on the board while leaving a "while 1; do
fastboot boot boot.img; done" on the host pc.

The issue is present in mainline up to 5.2-rc4, using defconfig and:

CONFIG_SCSI_UFS_QCOM=y
CONFIG_PHY_QCOM_QMP=y
CONFIG_PHY_QCOM_UFS=y

but was present in previous releases too (e.g. 4.14., 4.19, etc qcom-lt or
mainline), where it's even easier to reproduce (e.g. takes way less reboots to
trigger it).

These are the last lines printed out:
...
[    7.407209] qcom-qmp-phy 34000.phy: Registered Qcom-QMP phy
[    7.448058] qcom-qmp-phy 7410000.phy: Registered Qcom-QMP phy
[    7.461859] ufs_qcom_phy_qmp_14nm 627000.phy: invalid resource
[    7.535434] qcom-qmp-phy 34000.phy: phy common block init timed-out
[    7.538596] phy phy-34000.phy.0: phy init failed --> -110
[    7.550891] qcom-pcie: probe of 600000.pcie failed with error -110
[    7.619008] qcom-pcie 608000.pcie: 608000.pcie supply vddpe-3v3 not found,
using dummy regulator

Log Type: B - Since Boot(Power On Reset),  D - Delta,  S - Statistic
S - QC_IMAGE_VERSION_STRING=BOOT.XF.1.0-00301
S - IMAGE_VARIANT_STRING=M8996LAB
S - OEM_IMAGE_VERSION_STRING=crm-ubuntu68
S - Boot Interface: UFS
S - Secure Boot: Off
...

Full boot here: https://pastebin.ubuntu.com/p/rtjVrD3yzk/

Any idea what is going on? Am i doing something wrong?
-- 
bye,
p.