Re: [PATCH 0/3] soc: qcom: Add download mode support for QTI platforms

[Trilok Soni]

Stephen,

On 8/12/2021 5:16 PM, Stephen Boyd wrote:
> Quoting Sai Prakash Ranjan (2021-08-12 02:17:39)
> > 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
> >   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