Message-ID: <e96e315c-69fb-bc7e-5d07-06909344ff65@quicinc.com>
Date: Tue, 6 May 2025 23:03:55 +0530
From: Shivendra Pratap <quic_spratap@...cinc.com>
To: Lorenzo Pieralisi <lpieralisi@...nel.org>
CC: 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 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.
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?

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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