Re: [PATCH v20 06/10] power: reset: Add psci-reboot-mode driver

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

On 27-03-2026 19:25, Lorenzo Pieralisi wrote:
> On Wed, Mar 04, 2026 at 11:33:06PM +0530, Shivendra Pratap wrote:
>> PSCI supports different types of resets like COLD reset, ARCH WARM
>> reset, vendor-specific resets. Currently there is no common driver that
>> handles all supported psci resets at one place. Additionally, there is
>> no common mechanism to issue the supported psci resets from userspace.
>>
>> Add a PSCI reboot mode driver and define two types of PSCI resets in the
>> driver as reboot-modes: predefined resets controlled by Linux
>> reboot_mode and customizable resets defined by SoC vendors in their
>> device tree under the psci:reboot-mode node.
>>
>> Register the driver with the reboot-mode framework to interface these
>> resets to userspace. When userspace initiates a supported command, pass
>> the reset arguments to the PSCI driver to enable command-based reset.
>>
>> This change allows userspace to issue supported PSCI reset commands
>> using the standard reboot system calls while enabling SoC vendors to
>> define their specific resets for PSCI.
>>
>> Signed-off-by: Shivendra Pratap <shivendra.pratap@oss.qualcomm.com>
>> ---
>>   drivers/power/reset/Kconfig            |  10 +++
>>   drivers/power/reset/Makefile           |   1 +
>>   drivers/power/reset/psci-reboot-mode.c | 119 +++++++++++++++++++++++++++++++++
>>   3 files changed, 130 insertions(+)
>>
>> diff --git a/drivers/power/reset/Kconfig b/drivers/power/reset/Kconfig
>> index f6c1bcbb57deff3568d6b1b326454add3b3bbf06..529d6c7d3555601f7b7e6199acd29838030fcef2 100644
>> --- a/drivers/power/reset/Kconfig
>> +++ b/drivers/power/reset/Kconfig
>> @@ -348,6 +348,16 @@ config NVMEM_REBOOT_MODE
>>   	  then the bootloader can read it and take different
>>   	  action according to the mode.
>>   
>> +config PSCI_REBOOT_MODE
>> +	bool "PSCI reboot mode driver"
>> +	depends on OF && ARM_PSCI_FW
>> +	select REBOOT_MODE
>> +	help
>> +	  Say y here will enable PSCI reboot mode driver. This gets
>> +          the PSCI reboot mode arguments and passes them to psci
>> +	  driver. psci driver uses these arguments for issuing
>> +	  device reset into different boot states.
>> +
>>   config POWER_MLXBF
>>   	tristate "Mellanox BlueField power handling driver"
>>   	depends on (GPIO_MLXBF2 || GPIO_MLXBF3) && ACPI
>> diff --git a/drivers/power/reset/Makefile b/drivers/power/reset/Makefile
>> index 0e4ae6f6b5c55729cf60846d47e6fe0fec24f3cc..49774b42cdf61fd57a5b70f286c65c9d66bbc0cb 100644
>> --- a/drivers/power/reset/Makefile
>> +++ b/drivers/power/reset/Makefile
>> @@ -40,4 +40,5 @@ obj-$(CONFIG_REBOOT_MODE) += reboot-mode.o
>>   obj-$(CONFIG_SYSCON_REBOOT_MODE) += syscon-reboot-mode.o
>>   obj-$(CONFIG_POWER_RESET_SC27XX) += sc27xx-poweroff.o
>>   obj-$(CONFIG_NVMEM_REBOOT_MODE) += nvmem-reboot-mode.o
>> +obj-$(CONFIG_PSCI_REBOOT_MODE) += psci-reboot-mode.o
>>   obj-$(CONFIG_POWER_MLXBF) += pwr-mlxbf.o
>> diff --git a/drivers/power/reset/psci-reboot-mode.c b/drivers/power/reset/psci-reboot-mode.c
>> new file mode 100644
>> index 0000000000000000000000000000000000000000..86bef195228b0924704c2936b99f6801c14ff1b1
>> --- /dev/null
>> +++ b/drivers/power/reset/psci-reboot-mode.c
>> @@ -0,0 +1,119 @@
>> +// SPDX-License-Identifier: GPL-2.0-only
>> +/*
>> + * Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
>> + */
>> +
>> +#include <linux/device/faux.h>
>> +#include <linux/device.h>
> 
> Nit: swap the two.

Ack. thanks.


>> +#include <linux/err.h>
>> +#include <linux/of.h>
>> +#include <linux/psci.h>
>> +#include <linux/reboot.h>
>> +#include <linux/reboot-mode.h>
>> +#include <linux/types.h>
>> +
>> +/*
>> + * Predefined reboot-modes are defined as per the values
>> + * of enum reboot_mode defined in the kernel: reboot.c.
>> + */
>> +static struct mode_info psci_resets[] = {
>> +	{ .mode = "warm", .magic = REBOOT_WARM},
>> +	{ .mode = "soft", .magic = REBOOT_SOFT},
>> +	{ .mode = "cold", .magic = REBOOT_COLD},
>> +};
>> +
>> +static void psci_reboot_mode_set_predefined_modes(struct reboot_mode_driver *reboot)
>> +{
>> +	INIT_LIST_HEAD(&reboot->predefined_modes);
>> +	for (u32 i = 0; i < ARRAY_SIZE(psci_resets); i++) {
>> +		/* Prepare the magic with arg1 as 0 and arg2 as per pre-defined mode */
>> +		psci_resets[i].magic = REBOOT_MODE_MAGIC(0, psci_resets[i].magic);
> 
> This looks weird to me, why can't we just initialize the array with the values
> directly ?

Ack. The idea was to avoid Typecasting. Will check on this.

>> +		INIT_LIST_HEAD(&psci_resets[i].list);
>> +		list_add_tail(&psci_resets[i].list, &reboot->predefined_modes);
>> +	}
>> +}
>> +
>> +/*
>> + * arg1 is reset_type(Low 32 bit of magic).
>> + * arg2 is cookie(High 32 bit of magic).
>> + * If reset_type is 0, cookie will be used to decide the reset command.
>> + */
>> +static int psci_reboot_mode_write(struct reboot_mode_driver *reboot, u64 magic)
>> +{
>> +	u32 reset_type = REBOOT_MODE_ARG1(magic);
>> +	u32 cookie = REBOOT_MODE_ARG2(magic);
>> +
>> +	if (reset_type == 0) {
>> +		if (cookie == REBOOT_WARM || cookie == REBOOT_SOFT)
>> +			psci_set_reset_cmd(true, 0, 0);
>> +		else
>> +			psci_set_reset_cmd(false, 0, 0);
>> +	} else {
>> +		psci_set_reset_cmd(true, reset_type, cookie);
>> +	}
> 
> I don't think that psci_set_reset_cmd() has the right interface (and this
> nested if is too complicated for my taste). All we need to pass is reset-type
> and cookie (and if the reset is one of the predefined ones, reset-type is 0
> and cookie is the REBOOT_* cookie).
> 
> Then the PSCI firmware driver will take the action according to what
> resets are available.
> 
> How does it sound ?

So we mean these checks will move to the psci driver? Sorry for 
re-iterating the question.

>> +
>> +	return NOTIFY_DONE;
>> +}
>> +
>> +static int psci_reboot_mode_register_device(struct faux_device *fdev)
>> +{
>> +	struct reboot_mode_driver *reboot;
>> +	int ret;
>> +
>> +	reboot = devm_kzalloc(&fdev->dev, sizeof(*reboot), GFP_KERNEL);
>> +	if (!reboot)
>> +		return -ENOMEM;
>> +
>> +	psci_reboot_mode_set_predefined_modes(reboot);
>> +	reboot->write = psci_reboot_mode_write;
>> +	reboot->dev = &fdev->dev;
>> +
>> +	ret = devm_reboot_mode_register(&fdev->dev, reboot);
>> +	if (ret) {
>> +		dev_err_probe(&fdev->dev, ret, "devm_reboot_mode_register failed %d\n", ret);
>> +		return ret;
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +static int __init psci_reboot_mode_init(void)
>> +{
>> +	struct device_node *psci_np;
>> +	struct faux_device *fdev;
>> +	struct device_node *np;
>> +	int ret;
>> +
>> +	psci_np = of_find_compatible_node(NULL, NULL, "arm,psci-1.0");
>> +	if (!psci_np)
>> +		return -ENODEV;
>> +	/*
>> +	 * Look for reboot-mode in the psci node. Even if the reboot-mode
>> +	 * node is not defined in psci, continue to register with the
>> +	 * reboot-mode driver and let the dev.ofnode be set as NULL.
>> +	 */
>> +	np = of_find_node_by_name(psci_np, "reboot-mode");
>> +
>> +	fdev = faux_device_create("psci-reboot-mode", NULL, NULL);
> 
> Same comment as Bartosz (have you picked up his work and working towards
> a solution) ?
Working on this via MFD. Some issue as again MFD framework does not 
allows a fwnode based driver registration. Will update.

thanks,
Shivendra