Re: [PATCH v3 2/3] firmware: qcom: scm: Expose download-mode control

From: Stephen Boyd
Date: Thu Aug 10 2017 - 19:48:19 EST


On 08/09/2017 01:10 PM, Bjorn Andersson wrote:
> In order to aid post-mortem debugging the Qualcomm platforms provides a

s/provides/provide/

> "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

s/somehwere/somewhere/

> 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 <bjorn.andersson@xxxxxxxxxx>
> ---
>
> Changes since v2:
> - Define memory address by reference to TCSR
> - Provide Kconfig option for defaulting to enabled
> - Provided some comment in the code
>
> Changes since v1:
> - Specify DT propert being two-cell
> - Correct handling of scm-call return code
>
> .../devicetree/bindings/firmware/qcom,scm.txt | 2 +
> drivers/firmware/Kconfig | 11 ++++
> drivers/firmware/qcom_scm-32.c | 6 ++
> drivers/firmware/qcom_scm-64.c | 13 ++++
> drivers/firmware/qcom_scm.c | 69 ++++++++++++++++++++++
> drivers/firmware/qcom_scm.h | 2 +
> 6 files changed, 103 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/firmware/qcom,scm.txt b/Documentation/devicetree/bindings/firmware/qcom,scm.txt
> index 20f26fbce875..838dba841797 100644
> --- a/Documentation/devicetree/bindings/firmware/qcom,scm.txt
> +++ b/Documentation/devicetree/bindings/firmware/qcom,scm.txt
> @@ -18,6 +18,8 @@ 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: phandle reference to the TCSR hardware block containing the
> + download mode control register (optional)
>
> Example for MSM8916:
>
> diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
> index 6e4ed5a9c6fd..ed23c77d6361 100644
> --- a/drivers/firmware/Kconfig
> +++ b/drivers/firmware/Kconfig
> @@ -215,6 +215,17 @@ config QCOM_SCM_64
> def_bool y
> depends on QCOM_SCM && ARM64
>
> +config QCOM_SCM_DOWNLOAD_MODE_DEFAULT
> + bool "Qualcomm Download mode enabled by default"

Decapitalize download?

> + depends on QCOM_SCM
> + help
> + A device with "download mode" enabled will upon an unexpected
> + warm-restart enter a special debug mode that allows the user to
> + "download" memory content over USB for offline postmortem analysis.
> + The feature can be enabled/disabled on the kernel command line.
> +
> + Say Y here to enable "download mode" by default.
> +

otherwise

Reviewed-by: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>

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