Hi Sudeep and Sebastian, On Wed, Jun 19, 2024 at 08:28:06AM -0700, Elliot Berman wrote: > On Wed, Jun 19, 2024 at 02:51:43PM +0100, Sudeep Holla wrote: > > On Mon, Jun 17, 2024 at 10:18:09AM -0700, Elliot Berman wrote: > > > 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. > > > > > > > I need to think through it but when you first introduced the generic > > Documentation/devicetree/bindings/power/reset/reboot-mode.yaml bindings > > I also looked at drivers/power/reset/reboot-mode.c > > > > I assumed this extension to that binding would reuse the same and > > PSCI would just do reboot_mode_register(). I didn't expect to see these > > changes. I might have missing something but since the bindings is still > > quite generic with additional cells that act as additional cookie for > > reboot call, I still think that should be possible. > > > > What am I missing here then ? > > > > Right, if that was only thing to "solve" to make it easy to use > reboot-mode framework, I agree we should update reboot mode framework to > work with the additional cells. There are a few other issues I mention > above which, when combined, make me feel that PSCI is different enough > from how reboot mode framework works that we shouldn't try to make PSCI > work with the framework. Issues #1 and #2 are pretty easy to solve > (whether they should be solved is different); I'm not sure a good > approach to issue #3. > Does the reasoning I mention in the commit text make sense why PSCI should avoid using the reboot-mode.c framework? Thanks, Elliot
