On Mon, Mar 03, 2025 at 01:08:31PM -0800, Elliot Berman wrote: > From: Elliot Berman <elliot.berman@xxxxxxxxxxxxxxxx> > > 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. I have managed to discuss a little bit this patchset over the last few days and I think we have defined a plan going forward. A point that was raised is: https://man7.org/linux/man-pages/man2/reboot.2.html LINUX_REBOOT_CMD_RESTART2 *arg command, what is it supposed to represent ? Is it the mode the system should reboot into OR it is the actual command to be issued (which is what this patchset implements) ? LINUX_REBOOT_CMD_RESTART "..a default restart..." It is unclear what "default" means. We wonder whether the reboot_mode variable was introduced to _define_ that "default". So, in short, my aim is trying to decouple reboot_mode from the LINUX_REBOOT_CMD_RESTART2 *arg command. I believe that adding a sysfs interface to reboot-mode driver infrastructure would be useful, so that the commands would be exposed to userspace and userspace can set the *arg command specifically to issue a given reset/mode. I wonder why this is not already in place for eg syscon-reboot-mode resets, how does user space issue a command in those systems if the available commands aren't exposed to userspace ? Is there a kernel entity exposing those "modes" to userspace, somehow ? > 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. This can be changed and I think it should, so that the reboot modes are exposed to user space and PSCI can use that. > 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. > > Signed-off-by: Elliot Berman <elliot.berman@xxxxxxxxxxxxxxxx> > --- > drivers/firmware/psci/psci.c | 105 +++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 105 insertions(+) > > diff --git a/drivers/firmware/psci/psci.c b/drivers/firmware/psci/psci.c > index a1ebbe9b73b136218e9d9f9b8daa7756b3ab2fbe..6f8c47deaec0225f26704e1f3bcad52603127a85 100644 > --- a/drivers/firmware/psci/psci.c > +++ b/drivers/firmware/psci/psci.c > @@ -80,6 +80,14 @@ static u32 psci_cpu_suspend_feature; > static bool psci_system_reset2_supported; > static bool psci_system_off2_hibernate_supported; > > +struct psci_reset_param { > + const char *mode; > + u32 reset_type; > + u32 cookie; > +}; > +static struct psci_reset_param *psci_reset_params __ro_after_init; > +static size_t num_psci_reset_params __ro_after_init; > + > static inline bool psci_has_ext_power_state(void) > { > return psci_cpu_suspend_feature & > @@ -306,9 +314,39 @@ static int get_set_conduit_method(const struct device_node *np) > return 0; > } > > +static int psci_vendor_system_reset2(const char *cmd) > +{ > + unsigned long ret; > + size_t i; > + > + for (i = 0; i < num_psci_reset_params; i++) { > + if (!strcmp(psci_reset_params[i].mode, cmd)) { > + ret = invoke_psci_fn(PSCI_FN_NATIVE(1_1, SYSTEM_RESET2), > + psci_reset_params[i].reset_type, > + psci_reset_params[i].cookie, 0); > + /* > + * if vendor reset fails, log it and fall back to > + * architecture reset types That's not what the code does. > + */ > + pr_err("failed to perform reset \"%s\": %ld\n", cmd, > + (long)ret); > + return 0; > + } > + } > + > + return -ENOENT; > +} > + > static int psci_sys_reset(struct notifier_block *nb, unsigned long action, > void *data) > { > + /* > + * try to do the vendor system_reset2 > + * If there wasn't a matching command, fall back to architectural resets > + */ > + if (data && !psci_vendor_system_reset2(data)) > + return NOTIFY_DONE; > + > if ((reboot_mode == REBOOT_WARM || reboot_mode == REBOOT_SOFT) && > psci_system_reset2_supported) { > /* > @@ -795,6 +833,73 @@ static const struct of_device_id psci_of_match[] __initconst = { > {}, > }; > > +#define REBOOT_PREFIX "mode-" > + > +static int __init psci_init_system_reset2_modes(void) > +{ > + const size_t len = strlen(REBOOT_PREFIX); > + struct psci_reset_param *param; > + struct device_node *psci_np __free(device_node) = NULL; > + struct device_node *np __free(device_node) = NULL; > + struct property *prop; > + size_t count = 0; > + u32 magic[2]; > + int num; > + > + if (!psci_system_reset2_supported) > + return 0; > + > + psci_np = of_find_matching_node(NULL, psci_of_match); > + if (!psci_np) > + return 0; > + > + np = of_find_node_by_name(psci_np, "reset-types"); > + if (!np) > + return 0; Related to my initial question above. If LINUX_REBOOT_CMD_RESTART2 *arg command, is the actual reset to be issued, should we add a default mode "cold" and, if SYSTEM_RESET2 is supported, a "warm" reset mode too ? It all boils down to what *arg represents - adding "cold" and "warm" modes would remove the dependency on reboot_mode for resets issued through LINUX_REBOOT_CMD_RESTART2, the question is whether this is the correct thing to do. Comments very welcome. Thanks, Lorenzo > + > + for_each_property_of_node(np, prop) { > + if (strncmp(prop->name, REBOOT_PREFIX, len)) > + continue; > + num = of_property_count_u32_elems(np, prop->name); > + if (num != 1 && num != 2) > + continue; > + > + count++; > + } > + > + param = psci_reset_params = > + kcalloc(count, sizeof(*psci_reset_params), GFP_KERNEL); > + if (!psci_reset_params) > + return -ENOMEM; > + > + for_each_property_of_node(np, prop) { > + if (strncmp(prop->name, REBOOT_PREFIX, len)) > + continue; > + > + num = of_property_read_variable_u32_array(np, prop->name, magic, > + 1, ARRAY_SIZE(magic)); > + if (num < 0) { > + pr_warn("Failed to parse vendor reboot mode %s\n", > + param->mode); > + kfree_const(param->mode); > + continue; > + } > + > + param->mode = kstrdup_const(prop->name + len, GFP_KERNEL); > + if (!param->mode) > + continue; > + > + /* Force reset type to be in vendor space */ > + param->reset_type = PSCI_1_1_RESET_TYPE_VENDOR_START | magic[0]; > + param->cookie = num > 1 ? magic[1] : 0; > + param++; > + num_psci_reset_params++; > + } > + > + return 0; > +} > +arch_initcall(psci_init_system_reset2_modes); > + > int __init psci_dt_init(void) > { > struct device_node *np; > > -- > 2.34.1 >
