Stephen,

On 8/12/2021 5:16 PM, Stephen Boyd wrote:

Quoting Sai Prakash Ranjan (2021-08-12 02:17:39)

quoted

Collecting ramdumps on QTI platforms mainly require two things,
SDI (System Debug Image) enabled firmware and kernel support to
configure download mode cookies and SDI settings. Ramdumps can
be collected once the system enters the download mode. To enter
download mode, magic values or cookies need to be set in IMEM
which is used by firmware to decide to enter download mode or not.
Download mode cookies remain the same across targets and SDI disable
register needs to be set or SDI needs to be disabled in case of normal
reboot since ramdumps are supposed to be for crash debugging and
not for every reboot. This series adds the kernel support required
to enter download mode.

I don't recall if we discussed this on the list, but I'd really prefer
that we don't make kernel changes to support this beyond implementing
PSCI SYSTEM_RESET2 support and then some sort of vendor specific (or if
ARM is willing to update the spec then ARM specific) reset command on
panic reboot paths. The idea is to set the cookie in the bootloader
before the kernel is booted, then any insta-reboots/watchdogs would go
into download mode, no special init code required to lay down the cookie

quoted

  create mode 100644 drivers/soc/qcom/download_mode.c

Some discussion by Elliot on the PSCI_SYSTEM_RESET2 and vendor bits was 
done here. You may want to check.

https://lkml.org/lkml/2020/2/24/1137

---Trilok Soni