Re: [PATCH v17 07/12] firmware: psci: Implement vendor-specific resets as reboot-mode

Shivendra Pratap
2025-11-18T17:42:00Z

On 11/18/2025 5:58 PM, Lorenzo Pieralisi wrote:
> On Mon, Nov 17, 2025 at 11:14:48PM +0530, Shivendra Pratap wrote:
>>
>>
>> On 11/10/2025 10:52 PM, Lorenzo Pieralisi wrote:
>>> On Sun, Nov 09, 2025 at 08:07:20PM +0530, Shivendra Pratap wrote:
>>>> SoC vendors have different types of resets which are controlled
>>>> through various hardware registers. For instance, Qualcomm SoC
>>>> may have a requirement that reboot with “bootloader” command
>>>> should reboot the device to bootloader flashing mode and reboot
>>>> with “edl” should reboot the device into Emergency flashing mode.
>>>> Setting up such reboots on Qualcomm devices can be inconsistent
>>>> across SoC platforms and may require setting different HW
>>>> registers, where some of these registers may not be accessible to
>>>> HLOS. These knobs evolve over product generations and require
>>>> more drivers. PSCI spec defines, SYSTEM_RESET2, vendor-specific
>>>> reset which can help align this requirement. Add support for PSCI
>>>> SYSTEM_RESET2, vendor-specific resets and align the implementation
>>>> to allow user-space initiated reboots to trigger these resets.
>>>>
>>>> Implement the PSCI vendor-specific resets by registering to the
>>>> reboot-mode framework.
>>>
>>> I think that we should expose to user space _all_ PSCI reset types,
>>> cold, warm + vendor specific - as a departure from using the reboot_mode
>>> variable (and possibly deprecate it - or at least stop using it).
>>
>> sure. We can try that. Have tried to compile it all at the end of this thread.
>>
>>>
>>>> As psci init is done at early kernel init, reboot-mode registration cannot
>>>> be done at the time of psci init. This is because reboot-mode creates a
>>>> “reboot-mode” class for exposing sysfs, which can fail at early kernel init.
>>>> To overcome this, introduce a late_initcall to register PSCI vendor-specific
>>>> resets as reboot modes. Implement a reboot-mode write function that sets
>>>> reset_type and cookie values during the reboot notifier callback. Introduce
>>>> a firmware-based call for SYSTEM_RESET2 vendor-specific reset in the
>>>> psci_sys_reset path, using reset_type and cookie if supported by secure
>>>> firmware. Register a panic notifier and clear vendor_reset valid status
>>>> during panic. This is needed for any kernel panic that occurs post
>>>> reboot_notifiers.
>>>
>>> Is it because panic uses reboot_mode to determine the reset to issue ?
>>
>> Yes. As we know, currently psci supports only two resets,
>> psci_sys_reset2 (ARCH warm reset) and psci_sys_reset(COLD RESET). And kernel
>> panic path should take the path set by reboot_mode to maintain backward
>> compatibility.
>>
>>>
>>>> By using the above implementation, userspace will be able to issue
>>>> such resets using the reboot() system call with the "*arg"
>>>> parameter as a string based command. The commands can be defined
>>>> in PSCI device tree node under “reboot-mode” and are based on the
>>>> reboot-mode based commands.
>>>
>>> IMHO - it would be nice if could add mode-cold (or mode-normal in reboot mode
>>> speak) and mode-warm by default (if PSCI supports them) so that userspace
>>
>> Default mode in current kernel is cold, until explicitly set to warm.
>> So should it be defaulted to cold?
>
> I managed to confuse you sorry. What I wanted to say is that user space
> should be able to issue _all_ PSCI resets (inclusive of cold and warm if
> supported - ie if SYSTEM_RESET2 is supported) not just vendor resets.
>
> I misused "by default" - I meant cold and warm PSCI resets should be part
> of the reboot-mode list.
>
> [...]
>
>>>>
>>>> +struct psci_vendor_sysreset2 {
>>>> + u32 reset_type;
>>>> + u32 cookie;
>>>> + bool valid;
>>>> +};
>>>> +
>>>> +static struct psci_vendor_sysreset2 vendor_reset;
>>>
>>> I think this should represent all possible PSCI reset types, not vendor only
>>> and its value is set by the reboot mode framework.
>>>
>>>> +
>>>> +static int psci_panic_event(struct notifier_block *nb, unsigned long v, void *p)
>>>> +{
>>>> + vendor_reset.valid = false;
>>>
>>> I don't like this. Basically all you want this for is to make sure that
>>> we don't override the reboot_mode variable.
>>
>> Yes, it does not look good but as we planned to use reboot-mode framework earlier, which
>> sets the modes at the at reboot_notifiers. This needs to be taken care for any panic
>> that occurs between reboot_notifier and restart_notifier.
>
> Isn't there a simpler way to detect whether we are in panic mode and
> consequently we just issue a reset based on reboot_mode ?
>
> panic_in_progress() ?

Yes. panic_in_progress is added in 6.18.rc1. We can use that. Thanks. Seems i was
outdated.

>
>>> One (hack) would consist in checking the reboot_mode variable here and
>>> set the struct I mentioned above to the value represented in reboot_mode.
>>>
>>> Good luck if reboot_mode == REBOOT_GPIO :-)
>>
>> psci supports only two modes, ARCH_WARM and cold, so anything else except WARM/SOFT
>> should default to cold? So even if REBOOT_GPIO is set in reboot_mode, we should default
>> it to cold reset.
>>
>>>
>>>> + return NOTIFY_DONE;
>>>> +}
>>>> +
>>>> +static struct notifier_block psci_panic_block = {
>>>> + .notifier_call = psci_panic_event
>>>> +};
>>>> +
>>>> bool psci_tos_resident_on(int cpu)
>>>> {
>>>> return cpu == resident_cpu;
>>>> @@ -309,7 +330,10 @@ static int get_set_conduit_method(const struct device_node *np)
>>>> static int psci_sys_reset(struct notifier_block *nb, unsigned long action,
>>>> void *data)
>>>> {
>>>> - if ((reboot_mode == REBOOT_WARM || reboot_mode == REBOOT_SOFT) &&
>>>> + if (vendor_reset.valid && psci_system_reset2_supported) {
>>>> + invoke_psci_fn(PSCI_FN_NATIVE(1_1, SYSTEM_RESET2), vendor_reset.reset_type,
>>>> + vendor_reset.cookie, 0);
>>>
>>> See above. Two calls here: one for resets issued using the new userspace
>>> interface you are adding and legacy below - no vendor vs reboot_mode, this
>>> is a mess.
>>
>> Are we suggesting to completely remove the reboot_mode check from here in the new
>> design and base it on reboot <CMD> param?
>
> I am suggesting that there must be two reset options:
>
> - based on reboot mode set by user space
> - based on reboot_mode variable (as a fallback and while panic is in progress)
>
>>>
>>>> + } else if ((reboot_mode == REBOOT_WARM || reboot_mode == REBOOT_SOFT) &&
>>>> psci_system_reset2_supported) {
>>>> /*
>>>> * reset_type[31] = 0 (architectural)
>>>> @@ -547,6 +571,72 @@ static const struct platform_suspend_ops psci_suspend_ops = {
>>>> .enter = psci_system_suspend_enter,
>>>> };
>>>>
>>>> +static int psci_set_vendor_sys_reset2(struct reboot_mode_driver *reboot, u64 magic)
>>>> +{
>>>> + u32 magic_32;
>>>> +
>>>> + if (psci_system_reset2_supported) {
>>>> + magic_32 = magic & GENMASK(31, 0);
>>>> + vendor_reset.reset_type = PSCI_1_1_RESET_TYPE_VENDOR_START | magic_32;
>>>> + vendor_reset.cookie = (magic >> 32) & GENMASK(31, 0);
>>>
>>> Use FIELD_PREP/GET() please (but as mentioned above the vendor reset type
>>> bit[31] should be part of the reboot mode magic value, see above).
>>
>> sure. Will align this. thanks.
>>
>>>
>>>> + vendor_reset.valid = true;
>>>> + }
>>>> +
>>>> + return NOTIFY_DONE;
>>>> +}
>>>> +
>>>> +static int __init psci_init_vendor_reset(void)
>>>> +{
>>>> + struct reboot_mode_driver *reboot;
>>>> + struct device_node *psci_np;
>>>> + struct device_node *np;
>>>> + int ret;
>>>> +
>>>> + if (!psci_system_reset2_supported)
>>>> + return -EINVAL;
>>>> +
>>>> + psci_np = of_find_compatible_node(NULL, NULL, "arm,psci-1.0");
>>>> + if (!psci_np)
>>>> + return -ENODEV;
>>>> +
>>>> + np = of_find_node_by_name(psci_np, "reboot-mode");
>>>> + if (!np) {
>>>> + of_node_put(psci_np);
>>>> + return -ENODEV;
>>>> + }
>>>> +
>>>> + ret = atomic_notifier_chain_register(&panic_notifier_list, &psci_panic_block);
>>>> + if (ret)
>>>> + goto err_notifier;
>>>> +
>>>> + reboot = kzalloc(sizeof(*reboot), GFP_KERNEL);
>>>> + if (!reboot) {
>>>> + ret = -ENOMEM;
>>>> + goto err_kzalloc;
>>>> + }
>>>> +
>>>> + reboot->write = psci_set_vendor_sys_reset2;
>>>> + reboot->driver_name = "psci";
>>>> +
>>>> + ret = reboot_mode_register(reboot, of_fwnode_handle(np));
>>>> + if (ret)
>>>> + goto err_register;
>>>> +
>>>> + of_node_put(psci_np);
>>>> + of_node_put(np);
>>>> + return 0;
>>>> +
>>>> +err_register:
>>>> + kfree(reboot);
>>>> +err_kzalloc:
>>>> + atomic_notifier_chain_unregister(&panic_notifier_list, &psci_panic_block);
>>>> +err_notifier:
>>>> + of_node_put(psci_np);
>>>> + of_node_put(np);
>>>> + return ret;
>>>> +}
>>>> +late_initcall(psci_init_vendor_reset)
>>>
>>> I don't like adding another initcall here.
>>>
>>> I wonder whether this code belongs in a PSCI reboot mode driver, possibly a
>>> faux device in a way similar to what we did for cpuidle-psci (that after all
>>> is a consumer of PSCI_CPU_SUSPEND in a similar way as this code is a
>>> PSCI_SYSTEM_RESET{2} consumer), that communicates with
>>> drivers/firmware/psci/psci.c with the struct mentioned above.
>>
>> sure. we can create a new driver and try it as in cpuidle: cpuidle-psci.
>> Can you suggest a bit more on the overall approach we want to take here?
>> Have tried to summarize the potential changes and few questions below.
>>
>> - new driver registers a faux device - say - power: reset: psci_reset.
>
> Yes this could be a potential way forward but that's decoupled from the
> options below. If we take this route PSCI maintainers should be added
> as maintainers for this reboot mode driver.

you mean the new psci_reset driver? yes. Maintainer would be PSCI maintainer,
if we create a new psci_reset reboot mode driver.

>
>> - struct with pre-built psci reset_types - (warm, soft, cold). Currently
>> only two modes supported, anything other than warm/soft defaults to cold.
>> - vendor resets to be added as per vendor choice, inside psci device tree(SOC specific).
>> - psci_reset registers with reboot-mode for registering vendor resets. Here, we
>> have a problem, the pre-built psci reset_types - (warm, soft, cold) cannot be added via
>> reboot-mode framework.
>
> Why ?

If we want the new psci_reset to take the reboot-mode framework route, is it ok to
add default modes (warm, cold) in the device tree?
If not, then the design of reboot-mode framework(power:reset:reboot-mode.c) needs to be
further changed to equip this new feature.

If new psci_reset driver move away from reboot-mode framework(power:reset:reboot-mode.c), the driver
can have its own design, its own sysfs interface and maintained under psci Maintainer.

>
>> Should the new psci_reset driver, move away from reboot-mode
>> framework as-well? And define its own parsing logic for psci_reset_types,
>> and have its own restart_notifier instead of reboot_notifier?
>
> No. As I said earlier, I think it makes sense to allow user space to
> select _all_ PSCI reset types - architected and vendor specific in
> a single reboot mode driver.
>
> I believe that we must be able to have two well defined ways for
> issuing resets:
>
> - one based on reboot mode driver
> - one based on reboot_mode variable interface

So may be in more details-
user space issues - reboot cold
-> go for psci_reset (as psci_sysrest2 does not has cold reset?)
user space issues - reboot warm or a vendor_reset
-> if psci_sysreset2 is supported - call psci_sysreset2 with required params.
-> else
-> go for psci_reset COLD

user space issues - reboot (no commands) or a panic_in_progress
-> fallback to reboot_mode
-> if (reboot_mode == WARM and psci_sysreset2 is supported )
-> call psci_sysreset2 (ARCH WARM RESET)
-> else
-> go for psci_reset COLD

And we want to do this in two conditional statements in firmware:psci: psci_sys_reset
function?
Or am i not getting the point here?

thanks,
Shivendra

>
> Does this make sense everyone ? I don't know the history behind
> reboot_mode and the reboot mode driver framework I am just stating
> what I think makes sense to do for PSCI.
>
> Thanks,
> Lorenzo
>
>> - If new psci_reset driver move away from reboot-mode, we can get rid of the panic_notifier
>> added in the psci code. Else, we may still need the panic_notifier for any kernel panic
>> that occurs between reboot_notifier and restart_notifier?
>> - psci driver will export a function which will be called externally to set the current
>> psci reset_type.
>> - psci_sys_reset in psci driver should remove the check on reboot_mode. It will default to
>> cold reset (for the reason the current kernel defaults to cold reset in psci.)
>> example change in psci_sys_reset:
>> if(psci_system_reset2_supported && <psci_reset_new_struct_var> != cold)
>> psci_sys_reset2(AS PER PARAMS FROM new psci_reset driver)
>> else
>> psci_sys_reset(COLD RESET)
>>
>> thanks,
>> Shivendra