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

[Shivendra Pratap <quic_spratap@quicinc.com>]

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?
> 
>>>
>>>>
>>>> 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
>>>>>>>>>>
>>>
> 
>