On Fri, Apr 19, 2024 at 09:53:45AM +0100, Sudeep Holla wrote: > On Wed, Apr 17, 2024 at 02:54:41PM -0700, Elliot Berman wrote: > > 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. > > Fair enough. But I assume you are not providing the details of PMIC register > or IMEM cookie via DT. Kernel doesn't need this info. > > Anyways you did confirm if PSCI SYSTEM_RESET works as expected or not. That > is default and must work. > Yes, SYSTEM_RESET works on Quacomm firmware. The bindings disallow trying to override the default reboot. (reboot command = NULL or "") The PSCI parsing of the DT also doesn't have any of the special handling to deal with "mode-normal". > > > > 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. > > > > Yes and as usual DT has become dumping ground for firmware that don't > make things discoverable. Make crap that Qcom puts in the DT are firmware > related and can be make discoverable. Anyways it is sad that no efforts > to make it so are done as DT is always there to provide shortcuts. > > > - 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. > > You are right, but that is the only example I can see and it was done > in very early days of PSCI. It shouldn't be example if there are better > ways. > > > - 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. > > Correct but it can be Qcom specific firmware interface. There are so many > already. This splitting information between firmware and DT works well > for vertically integrated things which probably is the case with most of > Qcom SoCs but it is prone to issues if DT and firmware mismatch. Firmware > discovery eliminates such issues. > I worry about designing interfaces both in Qualcomm firmware and in the PSCI driver which doesn't really suit handling the discovery. We can implement the dynamic discovery mechanims once there is a board which needs it. Thanks, Elliot
