Re: [PATCH v13 07/10] firmware: psci: Implement vendor-specific resets as reboot-mode

["André Draszik" <andre.draszik@linaro.org>]

On Sun, 2025-07-27 at 21:54 +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.
> 
> 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.
> 
> 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 as “reset-types” and are based on the
> reboot-mode based commands.
> 
> Signed-off-by: Shivendra Pratap <shivendra.pratap@oss.qualcomm.com>
> ---
>  drivers/firmware/psci/Kconfig |  2 ++
>  drivers/firmware/psci/psci.c  | 57 ++++++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 58 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..e14bcdbec1750db8aa9297c8bcdb242f58cc420e 100644
> --- a/drivers/firmware/psci/psci.c
> +++ b/drivers/firmware/psci/psci.c
> @@ -17,6 +17,7 @@
>  #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 +52,14 @@ 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;
> +
>  bool psci_tos_resident_on(int cpu)
>  {
>  	return cpu == resident_cpu;
> @@ -309,7 +318,10 @@ 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);
> +	} else if ((reboot_mode == REBOOT_WARM || reboot_mode == REBOOT_SOFT) &&
>  	    psci_system_reset2_supported) {
>  		/*
>  		 * reset_type[31] = 0 (architectural)

I don't know the PSCI spec, but it looks like with this code it's not
possible to set a reboot mode (in DT) and at the same time instruct
the firmware whether a warm or a cold reboot was requested.

Doing warm reboot is useful if e.g. RAM contents needs to be retained
for crash recovery handling, or other reasons, while in normal cases
doing a more secure cold reboot.

On the other hand, of course it's useful to be able to specify the
reboot target for normal reboots.

Is this a problem with the PSCI spec or with this specific change
geared at the Qcom implementation?


> @@ -547,6 +559,49 @@ 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 & 0xFFFFFFFF;

I believe usual kernel style is to use lower case for
hex values.

> +		vendor_reset.reset_type = PSCI_1_1_RESET_TYPE_VENDOR_START | magic_32;
> +		vendor_reset.cookie = (magic >> 32) & 0xFFFFFFFF;

dito.

Cheers,
Andre'

> +		vendor_reset.valid = true;
> +	}
> +
> +	return NOTIFY_DONE;
> +}
> +
> +static int __init psci_init_vendor_reset(void)
> +{
> +	struct reboot_mode_driver *reboot;
> +	struct device_node *np;
> +	int ret;
> +
> +	np = of_find_node_by_path("/psci/reboot-mode");
> +	if (!np)
> +		return -ENODEV;
> +
> +	reboot = kzalloc(sizeof(*reboot), GFP_KERNEL);
> +	if (!reboot) {
> +		of_node_put(np);
> +		return -ENOMEM;
> +	}
> +
> +	reboot->write = psci_set_vendor_sys_reset2;
> +
> +	ret = reboot_mode_register(reboot, np, "psci");
> +	if (ret) {
> +		of_node_put(np);
> +		kfree(reboot);
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +late_initcall(psci_init_vendor_reset)
> +
>  static void __init psci_init_system_reset2(void)
>  {
>  	int ret;