Re: [PATCH v9 2/5] firmware: psci: Read and use vendor reset types

[Shivendra Pratap <quic_spratap@quicinc.com>]

On 6/19/2025 7:46 PM, Dmitry Baryshkov wrote:
> On Thu, 19 Jun 2025 at 15:32, Shivendra Pratap <quic_spratap@quicinc.com> wrote:
>>
>>
>>
>> On 6/19/2025 4:34 PM, Dmitry Baryshkov wrote:
>>> On 19/06/2025 12:00, Shivendra Pratap wrote:
>>>>
>>>>
>>>> On 6/18/2025 6:44 PM, Dmitry Baryshkov wrote:
>>>>> On Tue, May 06, 2025 at 11:03:55PM +0530, Shivendra Pratap wrote:
>>>>>>
>>>>>>
>>>>>> On 4/16/2025 5:35 PM, Lorenzo Pieralisi wrote:
>>>>>>> On Wed, Apr 09, 2025 at 11:48:24PM +0530, Shivendra Pratap wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>> On 4/8/2025 8:46 PM, Lorenzo Pieralisi wrote:
>>>>>>>>> On Tue, Mar 25, 2025 at 07:33:36PM +0530, Mukesh Ojha wrote:
>>>>>>>>>> On Fri, Mar 14, 2025 at 12:19:31PM +0100, Lorenzo Pieralisi wrote:
>>>>>>>>>>> On Mon, Mar 03, 2025 at 01:08:31PM -0800, Elliot Berman wrote:
>>>>>>>>>>>> From: Elliot Berman <elliot.berman@oss.qualcomm.com>
>>>>>>>>>>>>
>>>>>>>>>>>> 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.
>>>>>>>>>>>
>>>>>>>>>> In the case of a regular reboot or panic, the reboot/panic notifiers run
>>>>>>>>>> first, followed by the restart notifiers. The PSCI reset/reset2 should
>>>>>>>>>> be the last call from Linux, and ideally, this call should not fail.
>>>>>>>>>>
>>>>>>>>>> Reboot mode notifiers => restart notifiers or Panic notifiers => restart
>>>>>>>>>> notifiers
>>>>>>>>>>
>>>>>>>>>> So, if I understand correctly, you mean that we can change the reboot
>>>>>>>>>> mode framework to expose the arguments available to user space. We can
>>>>>>>>>> extend it to accept magic and cookies, save them in the reboot
>>>>>>>>>> framework, and retrieve them via a call from PSCI during a regular
>>>>>>>>>> reboot or panic based on the current arguments. Is this leading towards
>>>>>>>>>> writing an ARM-specific PSCI-reboot-mode driver, which in its reboot
>>>>>>>>>> notifier callback saves the magic and cookies, and these magic and
>>>>>>>>>> cookies will be used during psci_sys_reset2()? Or is there something
>>>>>>>>>> wrong with my understanding?
>>>>>>>>>
>>>>>>>>> No, you got it right (apologies for the delay in replying) - if the
>>>>>>>>> case for making reboot mode available to user space is accepted.
>>>>>>>>>
>>>>>> While moving this into reboot-mode framework, one more query came up.
>>>>>> The "ARM-specific PSCI-reboot-mode driver" that we are going to write needs
>>>>>> to be a Platform device driver for using reboot-mode framework.
>>>>>
>>>>> No, it doesn't. It rqeuires struct device, but there is no requirement
>>>>> for struct platform_device at any place.
>>>> yes, it can be struct device so may be create a virtual device
>>>> using reset-type node?
>>>
>>> It can be created, but I don't see a strong need for it.
>>>
>>>>>
>>>>>> As psci is not a platform device driver, a subdevice under it may not probe as a
>>>>>> platform driver. Is it ok to implement the "PSCI-reboot-mode driver" as a
>>>>>> early_initcall("psci_xyz") and then create a platform device something as
>>>>>> below or any other suggestions for this?
>>>>>
>>>>> Change struct reboot_mode_driver to pass corresponding of_node (or
>>>>> better fwnode) directly.  Corresponding device is used only in the
>>>>> reboot_mode_register() and only to access of-node or to print error
>>>>> messages.
>>>> struct reboot_mode_driver can be changed just to pass of_node. But then the other
>>>> suggestion was to expose sysfs from reboot-mode to show available commands.
>>>> For that we need a device. Any suggestion? A virtual device with reset-types node
>>>> passed to reboot-mode framework looks fine?
>>>
>>> You still don't need it. You'll create a new device, belonging to the new 'reboot' or 'reset' class to hold corresponding attributes.
>> just understand this - So the reboot-mode framework will create a new class
>> and a device and expose the supported commands?
> 
> Yes. Otherwise how would you create a vendor-independent userspace API?
Ack. thanks.
> 
>>>
>>>>>
>>>>>>
>>>>>> power:reset:<psci-vendor-reset-driver>:
>>>>>> -----
>>>>>> static int __init psci_vendor_reset_init(void) {
>>>>>> ..
>>>>>> ..
>>>>>>     np = of_find_node_by_name(NULL, "psci-vendor-reset");
>>>>>>     if(!np)
>>>>>>         return -ENODEV;
>>>>>>     pdev = of_platform_device_create(np, "psci-vendor-reset", NULL);
>>>>>> ..
>>>>>> ..
>>>>>> }
>>>>>> -------
>>>>>>
>>>>>> the sysfs we will expose from reboot-mode may show like below in above
>>>>>> implementation:
>>>>>>
>>>>>> ######
>>>>>> / # cat ./sys/devices/platform/psci-vendor-reset/available_modes
>>>>>> bootloader edl
>>>>>> ######
>>>>>>
>>>>>> thanks,
>>>>>> Shivendra
>>>>>>
>>>>>>>>
>>>>>>>> Agree that the available modes should be exposed to usespace via sysfs interface
>>>>>>>> and we should implement it. Also #1 and #2 can be handled via some
>>>>>>>> changes in the design as mentioned in above discussion.
>>>>>>>>
>>>>>>>> I have one doubt though when we implement this via reboot-mode framework.
>>>>>>>> The current patch implements PSCI ARM PSCI SYSTEM RESET2 vendor reset types.
>>>>>>>> psci driver is initialized very early at boot but potential ARM psci reboot-mode
>>>>>>>> driver will not probe at that stage and the ARM PSCI SYSTEM RESET2 vendor reset
>>>>>>>> types functionality will not be available in psci reset path until the reboot-mode
>>>>>>>> driver probes. Will this cause any limitation on usage of ARM's PSCI vendor-reset
>>>>>>>> types for early device resets?
>>>>>>>>
>>>>>>>> One use-case may be an early device crash or a early reset where a vendor
>>>>>>>> wants to use PSCI SYSTEM RESET2 vendor reset type to a reset the device to a
>>>>>>>> specific state but may not be able to use this driver.
>>>>>>>> (eg: a kernel panic at early boot where a vendor wants to reset device
>>>>>>>> to a specific state using vendor reset. Currently panic passes a NULL
>>>>>>>> (*arg command) while device reset but it may be explored for vendor specific
>>>>>>>> reset).
>>>>>>>
>>>>>>> As you said, that would not be a PSCI only issue - *if* we wanted to
>>>>>>> plug in this use case we should find a way to do it at reboot mode
>>>>>>> driver level.
>>>>>>>
>>>>>>> As a matter of fact, this is not a mainline issue AFAICS.
>>>>>>>
>>>>>>> Even if we did not design this as a reboot mode driver there would be a
>>>>>>> time window where you would not be able to use vendor resets on panic.
>>>>>>>
>>>>>>> I don't see it as a major roadblock at the moment.
>>>>>> Got it.
>>>>>>>
>>>>>>> Thanks,
>>>>>>> Lorenzo
>>>>>>>
>>>>>>>>
>>>>>>>> - Shivendra
>>>>>>>>
>>>>>>>>>> P.S. We appreciate Elliot for his work and follow-up on this while being
>>>>>>>>>> employed at Qualcomm.
>>>>>>>>>
>>>>>>>>> Yes I sincerely do for his patience, thank you.
>>>>>>>>>
>>>>>>>>> Lorenzo
>>>>>>>>>
>>>>>>>>>>>>   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@oss.qualcomm.com>
>>>>>>>>>>>> ---
>>>>>>>>>>>>   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.
>>>>>>>>>>>
>>>>>>>>>> Ack.
>>>>>>>>>>
>>>>>>>>>> -Mukesh
>>>>>>>>>>
>>>>>>>>>>>> +             */
>>>>>>>>>>>> +            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
>>>>>>>>>>>>
>>>>>
>>>
>>>
> 
> 
>