Re: [PATCH 0/3] soc: qcom: Add download mode support for QTI platforms
From: Sai Prakash Ranjan
Date: Mon Aug 16 2021 - 06:39:37 EST
On 2021-08-13 05:46, 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
or clear it on normal reboot. The normal reboot PSCI call would clear
the cookie in the firmware, in case something goes wrong after the
kernel hands off control to PSCI, and then panics that want to go into
download mode would make the SYSTEM_RESET2 reboot call into PSCI that
sets the cookie.
Maybe it could be a linux specific psci number or maybe we could
configure the reboot call in the psci node to be this specific number
so
that it can be different based on the firmware implementation if
consolidating around a single number doesn't work. Either way, that all
seems manageable and we can keep these cookie details out of the kernel
and the reboot/panic paths.
Alright, I think we can probably make it work without much/any changes
in kernel. So following what you said, we can just implement
PSCI_SYSTEM_RESET2 in firmware to enter the download mode having cookies
already set by default and the cookie is cleared when we have a normal
reboot via PSCI_SYSTEM_RESET. For panic reboot, we already have a
cmdline
*reboot=panic_warm* to identify panic reboots and can call into
PSCI_SYSTEM_RESET2. I have just tested and it works fine if we have
psci_system_reset2_supported as true.
@Trilok/@Elliot, you can check if above works for your usecases in
android
as well and it doesn't need any of your additional changes to kernel.
Thanks,
Sai
Currently this series doesn't add support for android targets where
a couple of SCM calls are required to set/unset the download mode
cookies and SDI configuration but can be easily added gradually to
the same driver, so as of now only chrome platforms are supported
and tested.
Sai Prakash Ranjan (3):
soc: qcom: Add download mode support
dt-bindings: msm: Add QTI download mode support binding
arm64: dts: qcom: sc7180: Add IMEM, pil info and download mode
region
.../bindings/arm/msm/qcom,dload-mode.yaml | 53 ++++++
MAINTAINERS | 7 +
arch/arm64/boot/dts/qcom/sc7180.dtsi | 21 +++
drivers/soc/qcom/Kconfig | 10 ++
drivers/soc/qcom/Makefile | 1 +
drivers/soc/qcom/download_mode.c | 152
++++++++++++++++++
6 files changed, 244 insertions(+)
create mode 100644
Documentation/devicetree/bindings/arm/msm/qcom,dload-mode.yaml
create mode 100644 drivers/soc/qcom/download_mode.c
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