On Tue, Apr 16, 2024 at 10:35:22AM +0100, Sudeep Holla wrote: > On Sun, Apr 14, 2024 at 12:30:23PM -0700, Elliot Berman wrote: > > The PSCI SYSTEM_RESET2 call allows vendor firmware to define additional > > reset types which could be mapped to the reboot argument. > > > > Setting up reboot on Qualcomm devices can be inconsistent from chipset > > to chipset. > > That doesn't sound good. Do you mean PSCI SYSTEM_RESET doesn't work as > expected ? Does it mean it is not conformant to the specification ? > I was motivating the reason for using SYSTEM_RESET2. How to set the PMIC register and IMEM cookie can change between chipsets. Using SYSTEM_RESET2 alows us to abstract how to perform the reset. > > Generally, there is a PMIC register that gets written to > > decide the reboot type. There is also sometimes a cookie that can be > > written to indicate that the bootloader should behave differently than a > > regular boot. These knobs evolve over product generations and require > > more drivers. Qualcomm firmwares are beginning to expose vendor > > SYSTEM_RESET2 types to simplify driver requirements from Linux. > > > > Why can't this be fully userspace driven ? What is the need to keep the > cookie in the DT ? As Dmitry pointed out, this information isn't discoverable. I suppose we could technically use bootconfig or kernel command-line to convey the map although I think devicetree is the right spot for this mapping. - Other vendor-specific bits for PSCI are described in the devicetree. One example is the suspend param (e.g. the StateID) for cpu idle states. - Describing firmware bits in the DT isn't unprecedented, and putting this information outside the DT means that other OSes (besides Linux) need their own way to convey this information. - PSCI would be the odd one out that reboot mode map is not described in DT. Other reboot-mode drivers specify the mapping in the DT. Userspace that runs with firmware that support vendor reset2 need to make sure they can configure the mapping early enough. Thanks, Elliot
