Message-ID: <d3e4417a-66cd-4e6e-590f-7a0e2bcfc0e6@quicinc.com>
Date: Thu, 19 Jun 2025 14:30:15 +0530
From: Shivendra Pratap <quic_spratap@...cinc.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.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>,
        Elliot Berman
	<elliot.berman@....qualcomm.com>,
        <quic_kaushalk@...inc.com>
Subject: Re: [PATCH v9 2/5] firmware: psci: Read and use vendor reset types



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

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