Re: [PATCH v6 0/4] regulator: qcom-rpmh: Support RPMH address reads and use it for rpmh-regulators

[Kanishka Chakraborty <kanishka.developer@gmail.com>]

Hi,

with this series in v7.3, SM7150 (Snapdragon 732G, Xiaomi Redmi Note 10
Pro) no longer boots. SM7150 support is not upstream yet; I am running
v7.3 with the sm7150-mainline patches on top, but the problem looks
independent of that and may affect other SoCs with older RSCs.

Symptom: the boot stops around the time the RPMh regulators register.
The display (left on by the bootloader) goes grey at that point and the
initramfs never runs, while the kernel apparently keeps running (the
watchdog keeps being serviced). The v7.1-based sm7150-mainline tree
boots fine on the same device with the same DT.

What I checked:

- Reverting 09d99ff7fc3c ("regulator: qcom-rpmh: readback
  voltage/bypass/mode set during bootup") and its follow-up 216e8873bc80
  ("regulator: qcom-rpmh: Fix coding style issues") makes v7.3 boot.

- A log-only variant that still issues every rpmh_read() but throws the
  results away (vreg->mode, bypassed and voltage_selector restored to the
  pre-readback defaults) hangs exactly the same way. So issuing the reads
  is enough to break it, independent of what is done with the values.
  I couldn't capture the per-read log lines: the display dies at that
  point and the boot never gets far enough for USB or a log.

- The apps RSC here reports RSC_DRV_ID = 0x00010100, i.e. version 1.1.
  rpmh-rsc only describes the v2.7 and v3.0 register layouts and uses the
  v2.7 one for everything below 3.0, so on this RSC the read path writes
  CMD_MSGID without the write bit and later reads RESP_DATA at the v2.7
  offset. This SoC has two active-only TCSes.

I don't know whether read requests are supported on RSC v1.x at all, or
only need a different register layout there. Would it make sense to only
issue reads on RSCs known to support them, and let rpmh_read() return
-EOPNOTSUPP otherwise, so the regulator driver falls back to the old
behaviour?

I'm happy to test patches or collect more data on this device.

Thanks,
Kanishka