Message-ID: <CAO9ioeVOwjpSJ37Z-mMUn2tsc9b6J=OEMhrK74OMf-BpriB8-g@mail.gmail.com>
Date: Thu, 19 Jun 2025 17:16:02 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Shivendra Pratap <quic_spratap@...cinc.com>
Cc: Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Mukesh Ojha <mukesh.ojha@....qualcomm.com>,
        Elliot Berman <quic_eberman@...cinc.com>,
        Bjorn Andersson <andersson@...nel.org>,
        Sebastian Reichel <sre@...nel.org>, Rob Herring <robh@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>, Vinod Koul <vkoul@...nel.org>,
        Andy Yan <andy.yan@...k-chips.com>,
        Mark Rutland <mark.rutland@....com>,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
        Arnd Bergmann <arnd@...db.de>, Olof Johansson <olof@...om.net>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, cros-qcom-dts-watchers@...omium.org,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Satya Durga Srinivasu Prabhala <quic_satyap@...cinc.com>,
        Melody Olvera <quic_molvera@...cinc.com>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Florian Fainelli <florian.fainelli@...adcom.com>,
        Stephen Boyd <swboyd@...omium.org>, linux-pm@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, Elliot Berman <elliotb317@...il.com>,
        quic_spratap@...inc.com, quic_kaushalk@...inc.com
Subject: Re: [PATCH v9 2/5] firmware: psci: Read and use vendor reset types

On Thu, 19 Jun 2025 at 15:32, Shivendra Pratap <quic_spratap@...cinc.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@....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?

> >
> >>>
> >>>>
> >>>> 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@....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
> >>>>>>>>>>
> >>>
> >
> >



-- 
With best wishes
Dmitry

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