[PATCH v8 3/6] firmware: psci: Read and use vendor reset types

[Stephen Boyd]

Quoting Elliot Berman (2024-11-07 15:38:27)
> SoC vendors have different types of resets and are controlled through
> various registers. For instance, Qualcomm chipsets can reboot to a
> "download mode" that allows a RAM dump to be collected. Another example
> is they also support writing a cookie that can be read by bootloader
> during next boot. PSCI offers a mechanism, SYSTEM_RESET2, for these
> vendor reset types to be implemented without requiring drivers for every
> register/cookie.
>
> Add support in PSCI to statically map reboot mode commands from
> userspace to a vendor reset and cookie value using the device tree.
>
> A separate initcall is needed to parse the devicetree, instead of using
> psci_dt_init because mm isn't sufficiently set up to allocate memory.
>
> Reboot mode framework is close but doesn't quite fit with the
> design and requirements for PSCI SYSTEM_RESET2. Some of these issues can
> be solved but doesn't seem reasonable in sum:
>  1. reboot mode registers against the reboot_notifier_list, which is too
>     early to call SYSTEM_RESET2. PSCI would need to remember the reset
>     type from the reboot-mode framework callback and use it
>     psci_sys_reset.
>  2. reboot mode assumes only one cookie/parameter is described in the
>     device tree. SYSTEM_RESET2 uses 2: one for the type and one for
>     cookie.
>  3. psci cpuidle driver already registers a driver against the
>     arm,psci-1.0 compatible. Refactoring would be needed to have both a
>     cpuidle and reboot-mode driver.
>
> Tested-by: Florian Fainelli <florian.fainelli at broadcom.com>
> Signed-off-by: Elliot Berman <quic_eberman at quicinc.com>
> ---

Reviewed-by: Stephen Boyd <swboyd at chromium.org>