Re: [PATCH v16 5/6] power: reset: Introduce PSCR Recording Framework for Non-Volatile Storage

[Bradley Morgan]

On 7 October 2026 08:06:40 BST, Faruque Ansari
<faruque.ansari@xxxxxxxxxxxxxxxx> wrote:
>Introduce the Power State Change Reasons Recording (PSCRR) framework: a
>generic mechanism to record why the last power state change (shutdown or
>reboot) happened - under-voltage, thermal, watchdog, software-triggered,
>etc. - so a postmortem reason survives a reboot or an abrupt power loss.
>
>PSCRR is built around providers. A provider is either a hardware reason
>source (a PMIC, SoC reset controller or watchdog exposing a reset cause)
>or a recorder that persists the reason across a power cycle (an NVMEM or
>RTC scratch cell). Each provider gets a directory under
>/sys/kernel/pscrr/providerN/ exposing its name, backing device, the set
>of observed reasons (as tokens), its capabilities, the reasons it
>supports and - for recorders - a record policy. The reason set is
>deliberately not collapsed to a single winning cause, since resets are
>often multi-causal.
>
>Reasons are the numeric enum psc_reason values from reboot.h, shared with
>the POWER_ON_REASON_* vocabulary, so they store compactly in small
>battery-backed cells. The current reason (get/set_psc_reason(), set by
>the thermal/regulator/hw_protection paths) is written to every recorder
>from the reboot notifier.
>
>Co-developed-by: Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx>
>Signed-off-by: Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx>
>Reported-by: Francesco Valla <francesco@xxxxxxxx>
>Closes: https://lore.kernel.org/all/178749889134.204450.5740187753642158305.b4-review@b4/
>Reviewed-by: Matti Vaittinen <mazziesaccount@xxxxxxxxx>

Hmm. LGTM from my standpoint:

Reviewed-by: Bradley Morgan <brads@xxxxxxxxxxxxxx>


>Signed-off-by: Faruque Ansari <faruque.ansari@xxxxxxxxxxxxxxxx>
>
>changes v15:
>- Use -EOPNOTSUPP for missing write_reason() support instead of -EPERM.
>- Use -EINVAL for unsupported reason values instead of -EOPNOTSUPP.
>- Add a comment explaining provider lifetime guarantees for sysfs callbacks.
>- Add Reviewed-by tags from Matti Vaittinen.
>
>changes v13:
>- Narrow pscrr_lock usage in pscrr_provider_register() to only protect
>  pscrr_dirs list updates.
>- Check pscrr_root before allocation and limit locking around
>  ida_alloc() and kobject/sysfs setup.
>changes v12:
>- rework into a multi-provider framework: one sysfs directory per
>  provider instead of a single backend
>- add per-provider capabilities, supported_reasons and record policy
>- register providers through a const ops table via
>  (devm_)pscrr_provider_register()
>- report reasons as parsable tokens
>- move the sources under drivers/power/reset/pscrr/
>- add a MAINTAINERS entry; PSCRR depends on POWER_RESET
>- drop Reviewed-by: Matti Vaittinen; the framework was substantially
>  reworked since it was given
>changes v10:
>- make g_pscrr static
>changes v8:
>- introduce struct pscrr_core to encapsulate backend and locking
>- replace global mutex and backend pointer with centralized pscrr_core
>- use DEFINE_GUARD() + guard(g_pscrr) for scoped mutex locking
>- simplify code using local backend pointer after locking
>- prepare code structure for future multi-backend support
>changes v7:
>- make write_reason optional
>- update documentation
>changes v6:
>- move enum pscr_reason to kernel reboot core
>- move reason storage to reboot core
>- add locking
>---
> MAINTAINERS                        |  11 +
> drivers/power/reset/Kconfig        |   2 +
> drivers/power/reset/Makefile       |   1 +
> drivers/power/reset/pscrr/Kconfig  |  33 ++
> drivers/power/reset/pscrr/Makefile |   2 +
> drivers/power/reset/pscrr/pscrr.c  | 640
> +++++++++++++++++++++++++++++++++++++
> include/linux/pscrr.h              | 107 +++++++
> 7 files changed, 796 insertions(+)
>
>diff --git a/MAINTAINERS b/MAINTAINERS
>index 05215fcc18a5..a7145dbb6eb7 100644
>--- a/MAINTAINERS
>+++ b/MAINTAINERS
>@@ -21967,6 +21967,17 @@ F:	Documentation/devicetree/bindings/connector/pcie-m2-e-connector.yaml
> F:	Documentation/devicetree/bindings/connector/pcie-m2-m-connector.yaml
> F:	drivers/power/sequencing/pwrseq-pcie-m2.c
> 
>+POWER STATE CHANGE REASON RECORDING (PSCRR)
>+M:	Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx>
>+M:	Faruque Ansari <faruque.ansari@xxxxxxxxxxxxxxxx>
>+R:	Pengutronix Kernel Team <kernel@xxxxxxxxxxxxxx>
>+L:	linux-pm@xxxxxxxxxxxxxxx
>+S:	Maintained
>+F:	Documentation/ABI/testing/sysfs-kernel-pscrr
>+F:	drivers/power/reset/pscrr/
>+F:	include/linux/pscrr.h
>+F:	tools/testing/selftests/pscrr/
>+
> POWER STATE COORDINATION INTERFACE (PSCI)
> M:	Mark Rutland <mark.rutland@xxxxxxx>
> M:	Lorenzo Pieralisi <lpieralisi@xxxxxxxxxx>
>diff --git a/drivers/power/reset/Kconfig b/drivers/power/reset/Kconfig
>index bce996bbef28..f24ff89dd94e 100644
>--- a/drivers/power/reset/Kconfig
>+++ b/drivers/power/reset/Kconfig
>@@ -377,3 +377,5 @@ config POWER_RESET_QEMU_VIRT_CTRL
> 	  provides this controller, such as the m68k virt machine.
> 
> endif
>+
>+source "drivers/power/reset/pscrr/Kconfig"
>diff --git a/drivers/power/reset/Makefile b/drivers/power/reset/Makefile
>index e31cab4ba78e..c73dc747e36c 100644
>--- a/drivers/power/reset/Makefile
>+++ b/drivers/power/reset/Makefile
>@@ -37,6 +37,7 @@ obj-$(CONFIG_POWER_RESET_KEYSTONE) += keystone-reset.o
> obj-$(CONFIG_POWER_RESET_SYSCON) += syscon-reboot.o
> obj-$(CONFIG_POWER_RESET_SYSCON_POWEROFF) += syscon-poweroff.o
> obj-$(CONFIG_POWER_RESET_RMOBILE) += rmobile-reset.o
>+obj-$(CONFIG_PSCRR) += pscrr/
> obj-$(CONFIG_REBOOT_MODE) += reboot-mode.o
> obj-$(CONFIG_SYSCON_REBOOT_MODE) += syscon-reboot-mode.o
> obj-$(CONFIG_POWER_RESET_SC27XX) += sc27xx-poweroff.o
>diff --git a/drivers/power/reset/pscrr/Kconfig b/drivers/power/reset/pscrr/Kconfig
>new file mode 100644
>index 000000000000..72de82731b53
>--- /dev/null
>+++ b/drivers/power/reset/pscrr/Kconfig
>@@ -0,0 +1,33 @@
>+# SPDX-License-Identifier: GPL-2.0-only
>+menuconfig PSCRR
>+	bool "Power State Change Reasons Recording (PSCRR) Framework"
>+	depends on POWER_RESET
>+	help
>+	  Enables the Power State Change Reasons Recording (PSCRR) framework.
>+
>+	  PSCRR records why the system last shut down or rebooted into
>+	  non-volatile storage, so the reason survives the reset and can be
>+	  read by the bootloader or early user space on the next boot. Reasons
>+	  come from software (thermal or regulator hardware-protection events,
>+	  a watchdog pretimeout, a kernel panic, a controlled reboot) or from
>+	  hardware reset-cause registers (PMIC, SoC reset controller, watchdog).
>+
>+	  It helps whenever the real cause would otherwise be lost or ambiguous
>+	  on the next boot, for example:
>+
>+	  - the reset is abrupt and block storage (eMMC/NAND) may not survive
>+	    it; on systems that can detect the event in time - such as an
>+	    imminent power loss with a short backup-capacitor window - the
>+	    reason can still be persisted first;
>+
>+	  - the hardware does not preserve the cause and the boot looks like a
>+	    plain power-on reset, e.g. a watchdog pretimeout that escalates
>+	    into a panic reboot would otherwise be indistinguishable from a
>+	    POR.
>+
>+	  The framework is extensible and exposes software-defined and
>+	  hardware-reported reasons through one interface. Sudden power cuts,
>+	  CPU freezes or other uncontrolled resets may still go unrecorded
>+	  unless hardware provides the reset cause.
>+
>+	  If unsure, say N.
>diff --git a/drivers/power/reset/pscrr/Makefile b/drivers/power/reset/pscrr/Makefile
>new file mode 100644
>index 000000000000..e5530a858971
>--- /dev/null
>+++ b/drivers/power/reset/pscrr/Makefile
>@@ -0,0 +1,2 @@
>+# SPDX-License-Identifier: GPL-2.0
>+obj-$(CONFIG_PSCRR) += pscrr.o
>diff --git a/drivers/power/reset/pscrr/pscrr.c b/drivers/power/reset/pscrr/pscrr.c
>new file mode 100644
>index 000000000000..f7c1478a50c4
>--- /dev/null
>+++ b/drivers/power/reset/pscrr/pscrr.c
>@@ -0,0 +1,640 @@
>+// SPDX-License-Identifier: GPL-2.0
>+/*
>+ * pscrr.c - Core Power State Change Reason Recording
>+ *
>+ * PSCRR records why the last power state change (shutdown/reboot) happened.
>+ * Reasons come from providers: hardware reset-cause registers (PMIC, SoC reset
>+ * controller, watchdog), persistent recorders (NVMEM/RTC scratch), the
>+ * bootloader's device-tree /chosen/reset-source (a built-in provider here), or
>+ * test stubs. Each provider gets a directory under /sys/kernel/pscrr/ and reports
>+ * the full set of reasons it observed - the picture is deliberately not
>+ * collapsed to a single "winning" cause, since resets are often multi-causal.
>+ *
>+ * Sysfs (per provider, under /sys/kernel/pscrr/providerN/):
>+ *   name               ro  human label of the provider
>+ *   device             symlink to the backing device (if any)
>+ *   reason             the provider's reason set, as tokens; writable (record
>+ *                      one reason) when the provider supports it
>+ *   caps               ro  non-default capabilities ("writable"); empty for a
>+ *                      read-only, single-slot provider
>+ *   supported_reasons  ro  reasons this provider can report or record
>+ *   record_policy      recorders only: keep the "first" or "last" reason
>+ *                      recorded in a power cycle
>+ *
>+ * The kernel keeps the first (root cause) and last power-state-change reason
>+ * (get_psc_first_reason()/get_psc_reason(), set by the thermal, regulator and
>+ * hw_protection paths). At reboot each recorder is given the first or the last
>+ * reason according to its record policy.
>+ *
>+ * Copyright (C) 2025 Pengutronix, Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx>
>+ * Copyright (c) 2025 Qualcomm Innovation Center, Inc. All rights reserved.
>+ */
>+
>+#define pr_fmt(fmt) "PSCRR: " fmt
>+
>+#include <linux/bitmap.h>
>+#include <linux/device.h>
>+#include <linux/idr.h>
>+#include <linux/kernel.h>
>+#include <linux/kobject.h>
>+#include <linux/list.h>
>+#include <linux/module.h>
>+#include <linux/mutex.h>
>+#include <linux/notifier.h>
>+#include <linux/of.h>
>+#include <linux/pscrr.h>
>+#include <linux/reboot.h>
>+#include <linux/slab.h>
>+#include <linux/string.h>
>+#include <linux/sysfs.h>
>+
>+static struct kobject *pscrr_root;
>+static DEFINE_MUTEX(pscrr_lock);
>+static LIST_HEAD(pscrr_dirs);
>+static DEFINE_IDA(pscrr_ida);
>+
>+/*
>+ * Record policy: when several reasons are recorded in one power cycle, keep the
>+ * first (root cause) or overwrite with the last. Global, tunable via sysfs.
>+ */
>+enum pscrr_record_policy {
>+	PSCRR_RECORD_FIRST,
>+	PSCRR_RECORD_LAST,
>+};
>+
>+/*
>+ * Per-provider sysfs directory. Core-owned and self-freeing on kobject_put(),
>+ * so its lifetime is decoupled from the caller-owned struct pscrr_provider.
>+ *
>+ * The sysfs show/store callbacks below dereference ->provider without
>+ * pscrr_lock: kobject_del() in pscrr_provider_unregister() blocks until
>+ * every in-flight callback on this kobject returns before the directory
>+ * (and thus ->provider) can be torn down, so a callback that is running
>+ * always sees a live provider.
>+ */
>+struct pscrr_provider_dir {
>+	struct kobject kobj;
>+	struct pscrr_provider *provider;
>+	struct list_head node;
>+	int id;
>+	enum pscrr_record_policy policy;	/* single-slot recorder: keep first/last */
>+	bool recorded;		/* a reason was recorded this power cycle */
>+};
>+
>+static inline struct pscrr_provider_dir *to_pscrr_dir(struct kobject *kobj)
>+{
>+	return container_of(kobj, struct pscrr_provider_dir, kobj);
>+}
>+
>+/*----------------------------------------------------------------------*/
>+/* Per-provider attributes */
>+/*----------------------------------------------------------------------*/
>+
>+static ssize_t name_show(struct kobject *kobj, struct kobj_attribute *attr,
>+			 char *buf)
>+{
>+	return sysfs_emit(buf, "%s\n", to_pscrr_dir(kobj)->provider->name);
>+}
>+
>+static struct kobj_attribute pscrr_name_attr = __ATTR_RO(name);
>+
>+static int pscrr_parse_reason(const char *buf, enum psc_reason *out)
>+{
>+	unsigned int val;
>+
>+	/* Accept either a decimal index or a reason token. */
>+	if (!kstrtouint(buf, 0, &val)) {
>+		if (val >= PSCR_REASON_COUNT)
>+			return -ERANGE;
>+		*out = val;
>+		return 0;
>+	}
>+
>+	return psc_reason_from_token(buf, out);
>+}
>+
>+static ssize_t reason_show(struct kobject *kobj, struct kobj_attribute *attr,
>+			   char *buf)
>+{
>+	struct pscrr_provider *p = to_pscrr_dir(kobj)->provider;
>+	DECLARE_BITMAP(reasons, PSCR_REASON_COUNT);
>+	ssize_t len = 0;
>+	int bit, ret;
>+
>+	bitmap_zero(reasons, PSCR_REASON_COUNT);
>+
>+	ret = p->ops->read_reasons(p, reasons);
>+	if (ret)
>+		return ret;
>+
>+	for_each_set_bit(bit, reasons, PSCR_REASON_COUNT)
>+		len += sysfs_emit_at(buf, len, "%s%s", len ? " " : "",
>+				     psc_reason_to_token(bit));
>+	len += sysfs_emit_at(buf, len, "\n");
>+
>+	return len;
>+}
>+
>+/* Record @reason into @dir honouring the global record policy. */
>+static int pscrr_do_record(struct pscrr_provider_dir *dir, enum psc_reason reason)
>+{
>+	struct pscrr_provider *p = dir->provider;
>+	int ret;
>+
>+	if (!p->ops->write_reason)
>+		return -EOPNOTSUPP;
>+
>+	/*
>+	 * PSCR_UNKNOWN clears the slot and releases the latch, regardless of
>+	 * policy, so a reason recorded afterwards is taken again.
>+	 */
>+	if (reason == PSCR_UNKNOWN) {
>+		ret = p->ops->write_reason(p, reason);
>+		if (ret)
>+			return ret;
>+
>+		dir->recorded = false;
>+		return 0;
>+	}
>+
>+	/* Reject reasons the provider does not advertise (NULL == all). */
>+	if (p->supported_reasons && !test_bit(reason, p->supported_reasons))
>+		return -EINVAL;
>+
>+	/* "first" policy: keep the first reason recorded this power cycle. */
>+	if (dir->policy == PSCRR_RECORD_FIRST && dir->recorded)
>+		return 0;
>+
>+	ret = p->ops->write_reason(p, reason);
>+	if (ret)
>+		return ret;
>+
>+	dir->recorded = true;
>+
>+	return 0;
>+}
>+
>+static ssize_t reason_store(struct kobject *kobj, struct kobj_attribute *attr,
>+			    const char *buf, size_t count)
>+{
>+	struct pscrr_provider_dir *dir = to_pscrr_dir(kobj);
>+	enum psc_reason reason;
>+	int ret;
>+
>+	if (!dir->provider->ops->write_reason)
>+		return -EOPNOTSUPP;
>+
>+	ret = pscrr_parse_reason(buf, &reason);
>+	if (ret)
>+		return ret;
>+
>+	/* Serialise the record state against concurrent stores and the notifier. */
>+	scoped_guard(mutex, &pscrr_lock)
>+		ret = pscrr_do_record(dir, reason);
>+	if (ret)
>+		return ret;
>+
>+	return count;
>+}
>+
>+static struct kobj_attribute pscrr_reason_attr =
>+	__ATTR(reason, 0644, reason_show, reason_store);
>+
>+static ssize_t caps_show(struct kobject *kobj, struct kobj_attribute *attr,
>+			 char *buf)
>+{
>+	struct pscrr_provider *p = to_pscrr_dir(kobj)->provider;
>+	ssize_t len = 0;
>+
>+	/* Readable and single-slot are the defaults and not listed. */
>+	if (p->ops->write_reason)
>+		len += sysfs_emit_at(buf, len, "writable");
>+
>+	return len + sysfs_emit_at(buf, len, "\n");
>+}
>+
>+static struct kobj_attribute pscrr_caps_attr = __ATTR_RO(caps);
>+
>+static ssize_t supported_reasons_show(struct kobject *kobj,
>+				      struct kobj_attribute *attr, char *buf)
>+{
>+	struct pscrr_provider *p = to_pscrr_dir(kobj)->provider;
>+	const unsigned long *sup = p->supported_reasons;
>+	ssize_t len = 0;
>+	int i;
>+
>+	for (i = 0; i < PSCR_REASON_COUNT; i++) {
>+		if (sup && !test_bit(i, sup))	/* NULL means all */
>+			continue;
>+		len += sysfs_emit_at(buf, len, "%s%s", len ? " " : "",
>+				     psc_reason_to_token(i));
>+	}
>+
>+	return len + sysfs_emit_at(buf, len, "\n");
>+}
>+
>+static struct kobj_attribute pscrr_supported_attr =
>+	__ATTR(supported_reasons, 0444, supported_reasons_show, NULL);
>+
>+static ssize_t record_policy_show(struct kobject *kobj,
>+				  struct kobj_attribute *attr, char *buf)
>+{
>+	struct pscrr_provider_dir *dir = to_pscrr_dir(kobj);
>+
>+	return sysfs_emit(buf, "%s\n",
>+			  READ_ONCE(dir->policy) == PSCRR_RECORD_FIRST ?
>+			  "first" : "last");
>+}
>+
>+static ssize_t record_policy_store(struct kobject *kobj,
>+				   struct kobj_attribute *attr,
>+				   const char *buf, size_t count)
>+{
>+	struct pscrr_provider_dir *dir = to_pscrr_dir(kobj);
>+
>+	guard(mutex)(&pscrr_lock);
>+
>+	if (sysfs_streq(buf, "first"))
>+		WRITE_ONCE(dir->policy, PSCRR_RECORD_FIRST);
>+	else if (sysfs_streq(buf, "last"))
>+		WRITE_ONCE(dir->policy, PSCRR_RECORD_LAST);
>+	else
>+		return -EINVAL;
>+
>+	return count;
>+}
>+
>+static struct kobj_attribute pscrr_record_policy_attr =
>+	__ATTR(record_policy, 0644, record_policy_show, record_policy_store);
>+
>+static struct attribute *pscrr_dir_attrs[] = {
>+	&pscrr_name_attr.attr,
>+	&pscrr_reason_attr.attr,
>+	&pscrr_caps_attr.attr,
>+	&pscrr_supported_attr.attr,
>+	&pscrr_record_policy_attr.attr,
>+	NULL,
>+};
>+
>+static umode_t pscrr_dir_is_visible(struct kobject *kobj, struct attribute *attr,
>+				    int n)
>+{
>+	struct pscrr_provider *p = to_pscrr_dir(kobj)->provider;
>+
>+	/* A provider without write_reason() exposes reason read-only. */
>+	if (attr == &pscrr_reason_attr.attr && !p->ops->write_reason)
>+		return 0444;
>+
>+	/* record_policy only applies to a (single-slot) recorder. */
>+	if (attr == &pscrr_record_policy_attr.attr && !p->ops->write_reason)
>+		return 0;
>+
>+	return attr->mode;
>+}
>+
>+static const struct attribute_group pscrr_dir_group = {
>+	.attrs		= pscrr_dir_attrs,
>+	.is_visible	= pscrr_dir_is_visible,
>+};
>+
>+static const struct attribute_group *pscrr_dir_groups[] = {
>+	&pscrr_dir_group,
>+	NULL,
>+};
>+
>+static void pscrr_dir_release(struct kobject *kobj)
>+{
>+	kfree(to_pscrr_dir(kobj));
>+}
>+
>+static const struct kobj_type pscrr_dir_ktype = {
>+	.sysfs_ops	= &kobj_sysfs_ops,
>+	.release	= pscrr_dir_release,
>+	.default_groups	= pscrr_dir_groups,
>+};
>+
>+/*----------------------------------------------------------------------*/
>+/* Provider registration */
>+/*----------------------------------------------------------------------*/
>+
>+/**
>+ * pscrr_provider_register - register a power state change reason provider
>+ * @p: caller-owned provider description
>+ *
>+ * Creates /sys/kernel/pscrr/providerN/ with "name" and "reason" attributes
>+ * and, when @p->dev is set, a "device" symlink. @p->reason is writable when
>+ * @p provides write_reason(). The provider must outlive the matching
>+ * pscrr_provider_unregister() call.
>+ *
>+ * Return: 0 on success or a negative errno.
>+ */
>+int pscrr_provider_register(struct pscrr_provider *p)
>+{
>+	struct pscrr_provider_dir *dir;
>+	int ret;
>+
>+	if (!p || !p->name || !p->ops || !p->ops->read_reasons)
>+		return -EINVAL;
>+
>+	/*
>+	 * pscrr_root is set once at core init and cleared at core exit;
>+	 * neither transition is serialised against this function by
>+	 * pscrr_lock, so check it up front rather than under the lock below.
>+	 */
>+	if (!pscrr_root)
>+		return -ENODEV;
>+
>+	dir = kzalloc_obj(*dir);
>+	if (!dir)
>+		return -ENOMEM;
>+
>+	dir->provider = p;
>+	dir->policy = PSCRR_RECORD_FIRST;
>+
>+	/* ida_alloc() and the kobject/sysfs calls below are individually thread-safe. */
>+	dir->id = ida_alloc(&pscrr_ida, GFP_KERNEL);
>+	if (dir->id < 0) {
>+		ret = dir->id;
>+		kfree(dir);
>+		return ret;
>+	}
>+
>+	ret = kobject_init_and_add(&dir->kobj, &pscrr_dir_ktype, pscrr_root,
>+				   "provider%d", dir->id);
>+	if (ret) {
>+		/*
>+		 * kobject_init_and_add() failed: per its contract only
>+		 * kobject_put() may follow, no kobject_del().
>+		 */
>+		ida_free(&pscrr_ida, dir->id);
>+		kobject_put(&dir->kobj);
>+		return ret;
>+	}
>+
>+	if (p->dev) {
>+		ret = sysfs_create_link(&dir->kobj, &p->dev->kobj, "device");
>+		if (ret)
>+			goto err_del;
>+	}
>+
>+	/* pscrr_lock only serialises pscrr_dirs against concurrent (un)registration. */
>+	scoped_guard(mutex, &pscrr_lock)
>+		list_add_tail(&dir->node, &pscrr_dirs);
>+
>+	return 0;
>+
>+err_del:
>+	kobject_del(&dir->kobj);
>+	ida_free(&pscrr_ida, dir->id);
>+	kobject_put(&dir->kobj);
>+	return ret;
>+}
>+EXPORT_SYMBOL_GPL(pscrr_provider_register);
>+
>+/**
>+ * pscrr_provider_unregister - remove a previously registered provider
>+ * @p: the provider passed to pscrr_provider_register()
>+ */
>+void pscrr_provider_unregister(struct pscrr_provider *p)
>+{
>+	struct pscrr_provider_dir *dir = NULL, *iter;
>+
>+	scoped_guard(mutex, &pscrr_lock) {
>+		list_for_each_entry(iter, &pscrr_dirs, node) {
>+			if (iter->provider == p) {
>+				dir = iter;
>+				list_del(&dir->node);
>+				break;
>+			}
>+		}
>+	}
>+
>+	if (!dir)
>+		return;
>+
>+	/*
>+	 * Tear the sysfs directory down outside pscrr_lock: kobject_del()
>+	 * drains in-flight reason/record_policy stores, which take pscrr_lock,
>+	 * so holding it here would deadlock. Release the id only once the
>+	 * directory is gone, so a concurrent register cannot reuse it and
>+	 * collide on the providerN name.
>+	 */
>+	if (p->dev)
>+		sysfs_remove_link(&dir->kobj, "device");
>+	kobject_del(&dir->kobj);
>+	ida_free(&pscrr_ida, dir->id);
>+	kobject_put(&dir->kobj);
>+}
>+EXPORT_SYMBOL_GPL(pscrr_provider_unregister);
>+
>+static void pscrr_provider_devm_release(void *p)
>+{
>+	pscrr_provider_unregister(p);
>+}
>+
>+/**
>+ * devm_pscrr_provider_register - device-managed reason provider registration
>+ * @dev: device the provider belongs to; also backs the "device" symlink
>+ * @name: human-readable provider label
>+ * @ops: provider callback table; read_reasons() is required, write_reason() is
>+ *	 optional and makes the provider a recorder
>+ * @supported_reasons: bitmap of the reasons the provider supports, or NULL
>+ *	 for all; set before the provider is exposed in sysfs
>+ * @priv: provider private data, handed back to the @ops callbacks
>+ *
>+ * Allocates and registers a struct pscrr_provider and schedules its
>+ * unregistration when @dev is unbound, so the caller keeps no reference to it.
>+ *
>+ * Return: the registered provider on success or an ERR_PTR() on failure. When
>+ * CONFIG_PSCRR is disabled the call resolves to a stub returning NULL, so
>+ * callers need no IS_ENABLED() guard.
>+ */
>+struct pscrr_provider *
>+devm_pscrr_provider_register(struct device *dev, const char *name,
>+			     const struct pscrr_provider_ops *ops,
>+			     const unsigned long *supported_reasons, void *priv)
>+{
>+	struct pscrr_provider *p;
>+	int ret;
>+
>+	p = devm_kzalloc(dev, sizeof(*p), GFP_KERNEL);
>+	if (!p)
>+		return ERR_PTR(-ENOMEM);
>+
>+	p->name = name;
>+	p->dev = dev;
>+	p->ops = ops;
>+	p->supported_reasons = supported_reasons;
>+	p->priv = priv;
>+
>+	ret = pscrr_provider_register(p);
>+	if (ret)
>+		return ERR_PTR(ret);
>+
>+	ret = devm_add_action_or_reset(dev, pscrr_provider_devm_release, p);
>+	if (ret)
>+		return ERR_PTR(ret);
>+
>+	return p;
>+}
>+EXPORT_SYMBOL_GPL(devm_pscrr_provider_register);
>+
>+/*----------------------------------------------------------------------*/
>+/* Record path: reboot notifier writes the current reason to recorders */
>+/*----------------------------------------------------------------------*/
>+
>+/*
>+ * Record the current power-state-change reason into every provider, giving
>+ * each the first (root cause) or the last reason according to its record
>+ * policy. The kernel keeps both, so "first" is meaningful even when later
>+ * events overwrite the last reason. The caller holds pscrr_lock, or runs where
>+ * the provider list is stable (panic).
>+ */
>+static void pscrr_record_current(void)
>+{
>+	enum psc_reason first = get_psc_first_reason();
>+	enum psc_reason last = get_psc_reason();
>+	struct pscrr_provider_dir *dir;
>+
>+	list_for_each_entry(dir, &pscrr_dirs, node)
>+		pscrr_do_record(dir, dir->policy == PSCRR_RECORD_FIRST ?
>+					     first : last);
>+}
>+
>+static int pscrr_reboot_notifier(struct notifier_block *nb,
>+				 unsigned long action, void *unused)
>+{
>+	guard(mutex)(&pscrr_lock);
>+
>+	/*
>+	 * A reboot, halt or power-off that reaches here with no more specific
>+	 * reason is software-initiated by definition. Record it as such rather
>+	 * than leaving it unattributed; a real cause set earlier (thermal,
>+	 * under-voltage, ...) is already latched and left untouched.
>+	 */
>+	if (get_psc_reason() == PSCR_UNKNOWN)
>+		set_psc_reason(PSCR_SOFTWARE);
>+
>+	pscrr_record_current();
>+
>+	return NOTIFY_DONE;
>+}
>+
>+static struct notifier_block pscrr_reboot_nb = {
>+	.notifier_call = pscrr_reboot_notifier,
>+};
>+
>+/*----------------------------------------------------------------------*/
>+/* Built-in provider: device-tree /chosen/reset-source                  */
>+/*----------------------------------------------------------------------*/
>+
>+/*
>+ * Bootloaders such as barebox record the SoC reset cause in the standard
>+ * device-tree /chosen/reset-source property. When it is present, surface it as
>+ * a read-only, device-less provider so the bootloader's view of the last reset
>+ * shows up next to any hardware or software providers - the framework just
>+ * reads the property already there, with no dedicated node or new binding.
>+ */
>+static const struct {
>+	const char *name;
>+	enum psc_reason reason;
>+} pscrr_reset_source_map[] = {
>+	{ "POR",      PSCR_POWER_ON },
>+	{ "RST",      PSCR_SOFTWARE },
>+	{ "WDG",      PSCR_WATCHDOG },
>+	{ "THERM",    PSCR_OVER_TEMPERATURE },
>+	{ "EXT",      PSCR_EXTERNAL },
>+	{ "BROWNOUT", PSCR_UNDER_VOLTAGE },
>+};
>+
>+static const unsigned long
>+pscrr_reset_source_supported[BITS_TO_LONGS(PSCR_REASON_COUNT)] = {
>+	BIT(PSCR_UNDER_VOLTAGE) | BIT(PSCR_OVER_TEMPERATURE) |
>+	BIT(PSCR_POWER_ON) | BIT(PSCR_WATCHDOG) | BIT(PSCR_SOFTWARE) |
>+	BIT(PSCR_EXTERNAL),
>+};
>+
>+/* Parsed once at init; read back by the provider's read_reasons(). */
>+static enum psc_reason pscrr_reset_source_reason = PSCR_UNKNOWN;
>+
>+static int pscrr_reset_source_read(struct pscrr_provider *p,
>+				   unsigned long *reasons)
>+{
>+	set_bit(pscrr_reset_source_reason, reasons);
>+
>+	return 0;
>+}
>+
>+static const struct pscrr_provider_ops pscrr_reset_source_ops = {
>+	.read_reasons = pscrr_reset_source_read,
>+};
>+
>+static struct pscrr_provider pscrr_reset_source_provider = {
>+	.name			= "reset-source",
>+	.ops			= &pscrr_reset_source_ops,
>+	.supported_reasons	= pscrr_reset_source_supported,
>+};
>+
>+static void __init pscrr_register_reset_source(void)
>+{
>+	const char *name;
>+	int i, ret;
>+
>+	if (!IS_ENABLED(CONFIG_OF) || !of_chosen)
>+		return;
>+
>+	if (of_property_read_string(of_chosen, "reset-source", &name))
>+		return;
>+
>+	for (i = 0; i < ARRAY_SIZE(pscrr_reset_source_map); i++)
>+		if (!strcmp(name, pscrr_reset_source_map[i].name)) {
>+			pscrr_reset_source_reason = pscrr_reset_source_map[i].reason;
>+			break;
>+		}
>+
>+	ret = pscrr_provider_register(&pscrr_reset_source_provider);
>+	if (ret)
>+		pr_warn("failed to register the reset-source provider: %d\n", ret);
>+}
>+
>+/*----------------------------------------------------------------------*/
>+/* Module init/exit */
>+/*----------------------------------------------------------------------*/
>+
>+static int __init pscrr_core_init(void)
>+{
>+	int ret;
>+
>+	pscrr_root = kobject_create_and_add("pscrr", kernel_kobj);
>+	if (!pscrr_root)
>+		return -ENOMEM;
>+
>+	ret = register_reboot_notifier(&pscrr_reboot_nb);
>+	if (ret) {
>+		kobject_put(pscrr_root);
>+		pscrr_root = NULL;
>+		return ret;
>+	}
>+
>+	pscrr_register_reset_source();
>+
>+	return 0;
>+}
>+
>+static void __exit pscrr_core_exit(void)
>+{
>+	pscrr_provider_unregister(&pscrr_reset_source_provider);
>+	unregister_reboot_notifier(&pscrr_reboot_nb);
>+	kobject_put(pscrr_root);
>+	pscrr_root = NULL;
>+	ida_destroy(&pscrr_ida);
>+}
>+
>+/* Bring the core up before device drivers probe and register providers. */
>+subsys_initcall(pscrr_core_init);
>+module_exit(pscrr_core_exit);
>+
>+MODULE_AUTHOR("Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx>");
>+MODULE_AUTHOR("Faruque Ansari <faruque.ansari@xxxxxxxxxxxxxxxx>");
>+MODULE_DESCRIPTION("Power State Change Reason Recording (PSCRR) core");
>+MODULE_LICENSE("GPL");
>diff --git a/include/linux/pscrr.h b/include/linux/pscrr.h
>new file mode 100644
>index 000000000000..330d6ac191bd
>--- /dev/null
>+++ b/include/linux/pscrr.h
>@@ -0,0 +1,107 @@
>+/* SPDX-License-Identifier: GPL-2.0 */
>+/*
>+ * pscrr.h - Public header for Power State Change Reason Recording (PSCRR).
>+ *
>+ * Copyright (C) 2025 Pengutronix, Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx>
>+ */
>+
>+#ifndef __PSCRR_H__
>+#define __PSCRR_H__
>+
>+#include <linux/reboot.h>
>+
>+struct device;
>+struct pscrr_provider;
>+
>+/**
>+ * struct pscrr_provider_ops - Provider callbacks.
>+ * @read_reasons: Fill @reasons with the complete set this source observed.
>+ *		@reasons is a bitmap of PSCR_REASON_COUNT bits; set members
>+ *		with set_bit(PSCR_x, reasons). Return 0 on success or a
>+ *		negative errno. Required. Driver state is reached via p->priv.
>+ * @write_reason: Persist @reason. Called from the reboot notifier for
>+ *		recorder-capable providers so the cause survives the power
>+ *		cycle. Leave NULL for read-only hardware sources.
>+ *
>+ * A const ops table per provider type; extend it with new callbacks without
>+ * touching the registration signature or existing callers.
>+ */
>+struct pscrr_provider_ops {
>+	int (*read_reasons)(struct pscrr_provider *p, unsigned long *reasons);
>+	int (*write_reason)(struct pscrr_provider *p, enum psc_reason reason);
>+};
>+
>+/**
>+ * struct pscrr_provider - A source (and optionally recorder) of power state
>+ *			   change reasons.
>+ *
>+ * A provider represents one place the system can learn *why* the last power
>+ * state change happened: a hardware reset-cause register (PMIC, SoC SRC,
>+ * watchdog), a persistent recorder (NVMEM/RTC scratch), or a test stub. Each
>+ * registered provider gets its own directory under /sys/kernel/pscrr/, so the
>+ * full, un-prioritised picture is visible: several providers - and several
>+ * reasons within one provider - can be reported simultaneously.
>+ *
>+ * @name:	Human-readable label, exported as the "name" attribute. The
>+ *		directory itself is core-indexed (providerN), so this need not
>+ *		be unique. Required.
>+ * @dev:	Backing device. When set it is exported as the "device" symlink
>+ *		in the provider directory, tying the reason to real hardware.
>+ *		May be NULL (e.g. for a test provider).
>+ * @ops:	Provider callbacks. Required.
>+ * @supported_reasons: Bitmap of the reasons this provider can store or report,
>+ *		limited e.g. by the storage size. 0 means all reasons.
>+ * @priv:	Provider private data, passed back through the callbacks.
>+ *
>+ * Providers are readable and single-slot by default; only capabilities beyond
>+ * that (currently: writable) are advertised.
>+ */
>+struct pscrr_provider {
>+	const char *name;
>+	struct device *dev;
>+	const struct pscrr_provider_ops *ops;
>+	const unsigned long *supported_reasons;
>+	void *priv;
>+};
>+
>+#if IS_ENABLED(CONFIG_PSCRR)
>+int pscrr_provider_register(struct pscrr_provider *p);
>+void pscrr_provider_unregister(struct pscrr_provider *p);
>+
>+/**
>+ * devm_pscrr_provider_register - allocate, fill and register a provider
>+ * @dev: device the provider belongs to (also the "device" symlink target)
>+ * @name: provider label
>+ * @ops: provider callbacks
>+ * @supported_reasons: bitmap of supported reasons, or NULL for all
>+ * @priv: driver state passed back through the callbacks
>+ *
>+ * The provider is unregistered automatically on device teardown.
>+ *
>+ * Return: the provider on success, ERR_PTR() on failure, or NULL when PSCRR
>+ * is not built (so the caller need not guard the call).
>+ */
>+struct pscrr_provider *
>+devm_pscrr_provider_register(struct device *dev, const char *name,
>+			     const struct pscrr_provider_ops *ops,
>+			     const unsigned long *supported_reasons, void *priv);
>+#else
>+static inline int pscrr_provider_register(struct pscrr_provider *p)
>+{
>+	return -EOPNOTSUPP;
>+}
>+
>+static inline void pscrr_provider_unregister(struct pscrr_provider *p)
>+{
>+}
>+
>+static inline struct pscrr_provider *
>+devm_pscrr_provider_register(struct device *dev, const char *name,
>+			     const struct pscrr_provider_ops *ops,
>+			     const unsigned long *supported_reasons, void *priv)
>+{
>+	return NULL;
>+}
>+#endif
>+
>+#endif /* __PSCRR_H__ */
>
>

--- Thanks!
"I'm not a very positive person" - Linus torvalds