Re: [PATCH 2/3] firmware: qcom: scm: Expose download-mode control

In order to aid post-mortem debugging the Qualcomm platforms provides a
"memory download mode", where the boot loader will provide an interface
for custom tools to "download" the content of RAM to a host machine.

The mode is triggered by writing a magic value somehwere in RAM, that is
read in the boot code path after a warm-restart. Two mechanism for
setting this magic value are supported in modern platforms; a direct SCM
call to enable the mode or through a secure io write of a magic value.

In order for a normal reboot not to trigger "download mode" the magic
must be cleared during a clean reboot.

Download mode has to be enabled by including qcom_scm.download_mode=1 on
the command line.

Signed-off-by: Bjorn Andersson <redacted>
---
 .../devicetree/bindings/firmware/qcom,scm.txt      |  1 +
 drivers/firmware/qcom_scm-32.c                     |  6 ++++
 drivers/firmware/qcom_scm-64.c                     | 16 +++++++++
 drivers/firmware/qcom_scm.c                        | 42 ++++++++++++++++++++++
 drivers/firmware/qcom_scm.h                        |  2 ++
 5 files changed, 67 insertions(+)

diff --git a/Documentation/devicetree/bindings/firmware/qcom,scm.txt b/Documentation/devicetree/bindings/firmware/qcom,scm.txt
index 20f26fbce875..8467a181f22c 100644
--- a/Documentation/devicetree/bindings/firmware/qcom,scm.txt
+++ b/Documentation/devicetree/bindings/firmware/qcom,scm.txt

@@ -18,6 +18,7 @@ Required properties:
  * Core, iface, and bus clocks required for "qcom,scm"
 - clock-names: Must contain "core" for the core clock, "iface" for the interface
   clock and "bus" for the bus clock per the requirements of the compatible.
+- qcom,dload-mode-addr: Specifies the address for the download mode magic (optional)