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

[Shivendra Pratap <shivendra.pratap@oss.qualcomm.com>]

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?

> could issue those resets too without having to set the reboot_mode variable.
> 
> Reason is, since we are doing this it is worth going the whole nine
> yards and try to decouple the reboot_mode variable from the RESTART2
> syscall argument.
> 
> Reworded: just use the new userspace interface you are adding for
> all PSCI reset types.
> 
> Thoughts very much welcome - I understand this is controversial.

We can remove the dependency on reboot_mode and include all supported
modes in a new psci_reset driver with some default modes (warm, cold)
and other vendor-specific resets which may be picked from device tree.
And then, reset based on the command being passed from userspace.

But yes some platforms that already reply on reboot_mode may break here
and will need to adjust to the new design being proposed.

Have summarized at the end of the thread.

> 
>> Reviewed-by: Umang Chheda <umang.chheda@oss.qualcomm.com>
>> Reviewed-by: Kathiravan Thirumoorthy <kathiravan.thirumoorthy@oss.qualcomm.com>
>> Reviewed-by: Nirmesh Kumar Singh <nirmesh.singh@oss.qualcomm.com>
>> Signed-off-by: Shivendra Pratap <shivendra.pratap@oss.qualcomm.com>
>> ---
>>  drivers/firmware/psci/Kconfig |  2 +
>>  drivers/firmware/psci/psci.c  | 92 ++++++++++++++++++++++++++++++++++++++++++-
>>  2 files changed, 93 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/firmware/psci/Kconfig b/drivers/firmware/psci/Kconfig
>> index 97944168b5e66aea1e38a7eb2d4ced8348fce64b..93ff7b071a0c364a376699733e6bc5654d56a17f 100644
>> --- a/drivers/firmware/psci/Kconfig
>> +++ b/drivers/firmware/psci/Kconfig
>> @@ -1,6 +1,8 @@
>>  # SPDX-License-Identifier: GPL-2.0-only
>>  config ARM_PSCI_FW
>>  	bool
>> +	select POWER_RESET
>> +	select REBOOT_MODE
>>  
>>  config ARM_PSCI_CHECKER
>>  	bool "ARM PSCI checker"
>> diff --git a/drivers/firmware/psci/psci.c b/drivers/firmware/psci/psci.c
>> index 38ca190d4a22d6e7e0f06420e8478a2b0ec2fe6f..ff82e7f4c27d1609a75cedc3a9790affaf839801 100644
>> --- a/drivers/firmware/psci/psci.c
>> +++ b/drivers/firmware/psci/psci.c
>> @@ -8,15 +8,18 @@
>>  
>>  #include <linux/acpi.h>
>>  #include <linux/arm-smccc.h>
>> +#include <linux/bitops.h>
>>  #include <linux/cpuidle.h>
>>  #include <linux/debugfs.h>
>>  #include <linux/errno.h>
>>  #include <linux/linkage.h>
>>  #include <linux/of.h>
>> +#include <linux/panic_notifier.h>
>>  #include <linux/pm.h>
>>  #include <linux/printk.h>
>>  #include <linux/psci.h>
>>  #include <linux/reboot.h>
>> +#include <linux/reboot-mode.h>
>>  #include <linux/slab.h>
>>  #include <linux/suspend.h>
>>  
>> @@ -51,6 +54,24 @@ static int resident_cpu = -1;
>>  struct psci_operations psci_ops;
>>  static enum arm_smccc_conduit psci_conduit = SMCCC_CONDUIT_NONE;
>>  
>> +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.

> 
> 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?

> 
>> +	} 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.
- 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. 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?
- 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