[PATCH v2 0/4] power: reset: add NVMEM recorder provider for PSCRR

[PATCH v2 0/4] power: reset: add NVMEM recorder provider for PSCRR

[Faruque Ansari]

The PSCRR framework[1] currently does not provide a recorder provider
capable of persisting power state change reasons across power cycles.

This series extends the PSCRR framework[1] with support for an
NVMEM-cell recorder provider, integrating PSCRR-recorded power state
change reasons with the NVMEM subsystem.

The recorder writes the power state change reason into a small NVMEM cell
(e.g. a PMIC SDAM byte or RTC scratch register) before shutdown or reset,
so the cause survives a power cycle and is available via
/sys/kernel/pscrr/ on the next boot.

Only the NVMEM-cell provider is included here. The PMIC hardware-register
provider will be submitted as a separate series.

Change in v2:
	- Add reviewers to To/Cc list.
	- Update patch 1/4:
	   * Rename DT node from pscr-reason to reboot-reason.
	   * Update DT binding example to use fixed-layout NVMEM layout.
	   * Add reboot_reason_persist NVMEM cell under fixed-layout.
	   * Update Qualcomm DTS example accordingly.
	- update patch 2/4 based on Uwe Kleine-König feedback:
	   * Remove unnecessary #include <linux/mod_devicetable.h>
	-v1-link: [2]

[1] https://lore.kernel.org/lkml/20260731095959.296056-1-o.rempel@pengutronix.de/
[2] https://lore.kernel.org/all/20260817-pscrr-provider-v1-0-88a318c13d41@oss.qualcomm.com/

Signed-off-by: Faruque Ansari <faruque.ansari@oss.qualcomm.com>
---
Faruque Ansari (4):
      dt-bindings: power: reset: add PSCRR NVMEM recorder binding
      power: reset: add PSCRR NVMEM recorder
      nvmem: provide consumer access to cell size metrics
      arm64: dts: qcom: lemans: Add PSCRR NVMEM recorder node

 .../bindings/power/reset/pscrr-nvmem.yaml          |  59 ++++++++
 MAINTAINERS                                        |   1 +
 arch/arm64/boot/dts/qcom/lemans-pmics.dtsi         |  16 +++
 drivers/nvmem/core.c                               |  29 ++++
 drivers/power/reset/pscrr/Kconfig                  |  14 ++
 drivers/power/reset/pscrr/Makefile                 |   1 +
 drivers/power/reset/pscrr/pscrr-nvmem.c            | 154 +++++++++++++++++++++
 include/linux/nvmem-consumer.h                     |   7 +
 8 files changed, 281 insertions(+)
---
base-commit: be461b2185ea3ff6d9c92deedcee0a62a57e1332
change-id: 20260806-pscrr-provider-b9f8f451701e

Best regards,
--  
Faruque Ansari <faruque.ansari@oss.qualcomm.com>

[PATCH v2 1/4] dt-bindings: power: reset: add PSCRR NVMEM recorder binding

[Faruque Ansari]

Add binding for the PSCRR NVMEM recorder. Records the power state
change reason into a small NVMEM cell, such as a PMIC SDAM byte or
RTC scratch register — so the cause survives a power cycle and can be
read back on the next boot.

Signed-off-by: Faruque Ansari <faruque.ansari@oss.qualcomm.com>
---
 .../bindings/power/reset/pscrr-nvmem.yaml          | 59 ++++++++++++++++++++++
 MAINTAINERS                                        |  1 +
 2 files changed, 60 insertions(+)

diff --git a/Documentation/devicetree/bindings/power/reset/pscrr-nvmem.yaml b/Documentation/devicetree/bindings/power/reset/pscrr-nvmem.yaml
new file mode 100644
index 000000000000..5334c923d644
--- /dev/null
+++ b/Documentation/devicetree/bindings/power/reset/pscrr-nvmem.yaml
@@ -0,0 +1,59 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/power/reset/pscrr-nvmem.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: NVMEM Power State Change Reason recorder
+
+maintainers:
+  - Faruque Ansari <faruque.ansari@oss.qualcomm.com>
+  - Oleksij Rempel <o.rempel@pengutronix.de>
+
+description:
+  An NVMEM-backed recorder for Power State Change Reasons (PSCRR). Persists
+  the reboot or shutdown cause into a small NVMEM cell, such as an RTC
+  scratch register, a PMIC SDAM (Scratch Data Access Memory) byte, or an
+  EEPROM — so the reason survives a power cycle and can be read back on the
+  next boot. The cell is referenced via the standard nvmem-cells consumer
+  binding.
+
+allOf:
+  - $ref: /schemas/nvmem/nvmem-consumer.yaml#
+
+properties:
+  compatible:
+    const: pscrr-nvmem
+
+  nvmem-cells:
+    maxItems: 1
+
+  nvmem-cell-names:
+    items:
+      - const: pscr
+
+required:
+  - compatible
+  - nvmem-cells
+  - nvmem-cell-names
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    nvmem-layout {
+        compatible = "fixed-layout";
+        #address-cells = <1>;
+        #size-cells = <1>;
+
+        reboot_reason_persist: reboot-reason-persist@49 {
+            reg = <0x49 0x1>;
+        };
+    };
+
+    reboot-reason {
+        compatible = "pscrr-nvmem";
+        nvmem-cells = <&reboot_reason_persist>;
+        nvmem-cell-names = "pscr";
+    };
+...
diff --git a/MAINTAINERS b/MAINTAINERS
index 19b9f6605d98..f329cd9d0491 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -21693,6 +21693,7 @@ R:	Pengutronix Kernel Team <kernel@pengutronix.de>
 L:	linux-pm@vger.kernel.org
 S:	Maintained
 F:	Documentation/ABI/testing/sysfs-kernel-pscrr
+F:	Documentation/devicetree/bindings/power/reset/pscrr-nvmem.yaml
 F:	drivers/power/reset/pscrr/
 F:	include/linux/pscrr.h
 F:	tools/testing/selftests/pscrr/

-- 
2.34.1

[PATCH v2 2/4] power: reset: add PSCRR NVMEM recorder

[Faruque Ansari]

Record the power state change reason into a small NVMEM cell (an RTC
scratch register or EEPROM) and read it back on the next boot, so the
cause survives a power cycle. The cell is a plain nvmem consumer
reference and the reason value is stored directly.

Co-developed-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Faruque Ansari <faruque.ansari@oss.qualcomm.com>
---
 drivers/power/reset/pscrr/Kconfig       |  14 +++
 drivers/power/reset/pscrr/Makefile      |   1 +
 drivers/power/reset/pscrr/pscrr-nvmem.c | 154 ++++++++++++++++++++++++++++++++
 3 files changed, 169 insertions(+)

diff --git a/drivers/power/reset/pscrr/Kconfig b/drivers/power/reset/pscrr/Kconfig
index 72de82731b53..bfcf04b0c8f5 100644
--- a/drivers/power/reset/pscrr/Kconfig
+++ b/drivers/power/reset/pscrr/Kconfig
@@ -31,3 +31,17 @@ menuconfig PSCRR
 	  unless hardware provides the reset cause.
 
 	  If unsure, say N.
+
+if PSCRR
+
+config PSCRR_NVMEM
+	tristate "PSCRR NVMEM recorder provider"
+	depends on NVMEM
+	help
+	  PSCRR recorder that stores the power state change reason in a
+	  small NVMEM cell (such as an RTC scratch register) and reads it
+	  back on the next boot, so the cause survives a power cycle.
+
+	  If unsure, say N.
+
+endif # PSCRR
diff --git a/drivers/power/reset/pscrr/Makefile b/drivers/power/reset/pscrr/Makefile
index e5530a858971..95c80c80c7da 100644
--- a/drivers/power/reset/pscrr/Makefile
+++ b/drivers/power/reset/pscrr/Makefile
@@ -1,2 +1,3 @@
 # SPDX-License-Identifier: GPL-2.0
 obj-$(CONFIG_PSCRR) += pscrr.o
+obj-$(CONFIG_PSCRR_NVMEM) += pscrr-nvmem.o
diff --git a/drivers/power/reset/pscrr/pscrr-nvmem.c b/drivers/power/reset/pscrr/pscrr-nvmem.c
new file mode 100644
index 000000000000..1c3145c0d058
--- /dev/null
+++ b/drivers/power/reset/pscrr/pscrr-nvmem.c
@@ -0,0 +1,154 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * pscrr-nvmem.c - NVMEM recorder provider for PSCRR
+ *
+ * Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
+ * Copyright (C) 2025 Pengutronix, Oleksij Rempel <o.rempel@pengutronix.de>
+ */
+
+#include <linux/module.h>
+#include <linux/nvmem-consumer.h>
+#include <linux/platform_device.h>
+#include <linux/pscrr.h>
+#include <linux/reboot.h>
+#include <linux/slab.h>
+
+struct pscrr_nvmem {
+	struct nvmem_cell *cell;
+	enum psc_reason reason;
+};
+
+static int pscrr_nvmem_cell_read(struct pscrr_nvmem *priv, u8 *out)
+{
+	size_t len;
+	void *buf;
+
+	buf = nvmem_cell_read(priv->cell, &len);
+	if (IS_ERR(buf))
+		return PTR_ERR(buf);
+
+	*out = len ? *(u8 *)buf : 0;
+	kfree(buf);
+
+	return 0;
+}
+
+static int pscrr_nvmem_cell_write(struct pscrr_nvmem *priv, u8 val)
+{
+	int ret;
+
+	/* nvmem_cell_write() returns the byte count on success, not 0. */
+	ret = nvmem_cell_write(priv->cell, &val, sizeof(val));
+
+	return ret < 0 ? ret : 0;
+}
+
+static int pscrr_nvmem_read_reasons(struct pscrr_provider *p,
+				    unsigned long *reasons)
+{
+	struct pscrr_nvmem *priv = p->priv;
+
+	/*
+	 * Report the reason latched at probe (or overwritten by a later
+	 * record); the cell itself was cleared at probe, so it is not read
+	 * live here.
+	 */
+	set_bit(READ_ONCE(priv->reason), reasons);
+
+	return 0;
+}
+
+static int pscrr_nvmem_write_reason(struct pscrr_provider *p,
+				    enum psc_reason reason)
+{
+	struct pscrr_nvmem *priv = p->priv;
+	int ret;
+
+	if (reason >= PSCR_REASON_COUNT)
+		return -EINVAL;
+
+	ret = pscrr_nvmem_cell_write(priv, reason);
+	if (ret)
+		return ret;
+
+	WRITE_ONCE(priv->reason, reason);
+
+	return 0;
+}
+
+static const struct pscrr_provider_ops pscrr_nvmem_ops = {
+	.read_reasons = pscrr_nvmem_read_reasons,
+	.write_reason = pscrr_nvmem_write_reason,
+};
+
+static int pscrr_nvmem_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct pscrr_nvmem *priv;
+	size_t bytes, bits;
+	u8 val;
+	int ret;
+
+	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->cell = devm_nvmem_cell_get(dev, "pscr");
+	if (IS_ERR(priv->cell))
+		return dev_err_probe(dev, PTR_ERR(priv->cell),
+				     "failed to get the pscr nvmem cell\n");
+
+	ret = nvmem_cell_get_size(priv->cell, &bytes, &bits);
+	if (ret)
+		return ret;
+
+	/* The reason is a single byte; a bit cell still occupies one. */
+	if ((bytes ?: DIV_ROUND_UP(bits, 8)) != sizeof(val))
+		return dev_err_probe(dev, -EINVAL,
+				     "unsupported pscr nvmem cell size\n");
+
+	/*
+	 * The cell survives resets, so at boot it still holds whatever the
+	 * previous session recorded before it went down. Latch that as this
+	 * boot's reason, then clear the cell back to PSCR_UNKNOWN: if this
+	 * session is later cut short by an abrupt reset that never runs the
+	 * recorder (watchdog power-cycle, sudden power loss), the next boot
+	 * reads "unknown" instead of a stale reason left over from an earlier
+	 * cycle.
+	 */
+	ret = pscrr_nvmem_cell_read(priv, &val);
+	if (ret)
+		return dev_err_probe(dev, ret,
+				     "failed to read the pscr nvmem cell\n");
+
+	priv->reason = val < PSCR_REASON_COUNT ? val : PSCR_UNKNOWN;
+
+	ret = pscrr_nvmem_cell_write(priv, PSCR_UNKNOWN);
+	if (ret)
+		return dev_err_probe(dev, ret,
+				     "failed to clear the pscr nvmem cell\n");
+
+	return PTR_ERR_OR_ZERO(devm_pscrr_provider_register(dev, "nvmem",
+							    &pscrr_nvmem_ops, NULL,
+							    priv));
+}
+
+static const struct of_device_id pscrr_nvmem_of_match[] = {
+	{ .compatible = "pscrr-nvmem" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, pscrr_nvmem_of_match);
+
+static struct platform_driver pscrr_nvmem_driver = {
+	.probe	= pscrr_nvmem_probe,
+	.driver	= {
+		.name		= "pscrr-nvmem",
+		.of_match_table	= pscrr_nvmem_of_match,
+	},
+};
+module_platform_driver(pscrr_nvmem_driver);
+
+MODULE_AUTHOR("Oleksij Rempel <o.rempel@pengutronix.de>");
+MODULE_AUTHOR("Faruque Ansari <faruque.ansari@oss.qualcomm.com>");
+MODULE_DESCRIPTION("NVMEM recorder provider for PSCRR");
+MODULE_LICENSE("GPL");

-- 
2.34.1

[PATCH v2 3/4] nvmem: provide consumer access to cell size metrics

[Faruque Ansari]

Add nvmem_cell_get_size() to let a consumer query a cell's size before
reading or writing it. Without this, a consumer that assumes a fixed
cell size can pass nvmem_cell_write() a buffer larger than the cell,
which fails with an incorrect-size error instead of succeeding with
the cell's actual capacity.

Co-developed-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Link: https://lore.kernel.org/lkml/dixmyhyj6b66vyizfotpqw6yzaavi2o2mauloa5x6zn3qgk5ub@huoal5ucdd44/
Signed-off-by: Faruque Ansari <faruque.ansari@oss.qualcomm.com>
---
 drivers/nvmem/core.c           | 29 +++++++++++++++++++++++++++++
 include/linux/nvmem-consumer.h |  7 +++++++
 2 files changed, 36 insertions(+)

diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index 0556d140170a..49afcff4c72c 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -1790,6 +1790,35 @@ int nvmem_cell_write(struct nvmem_cell *cell, void *buf, size_t len)
 
 EXPORT_SYMBOL_GPL(nvmem_cell_write);
 
+/**
+ * nvmem_cell_get_size() - Retrieve the storage size of an NVMEM cell.
+ * @cell: Pointer to the NVMEM cell structure.
+ * @bytes: Optional pointer to store the cell size in bytes (can be NULL).
+ * @bits: Optional pointer to store the cell size in bits (can be NULL).
+ *
+ * This function allows consumers to retrieve the size of a specific NVMEM
+ * cell before performing read/write operations. It is useful for validating
+ * buffer sizes to prevent mismatched writes.
+ *
+ * Return: 0 on success or negative on failure.
+ */
+int nvmem_cell_get_size(struct nvmem_cell *cell, size_t *bytes, size_t *bits)
+{
+	struct nvmem_cell_entry *entry = cell->entry;
+
+	if (!entry->nvmem)
+		return -EINVAL;
+
+	if (bytes)
+		*bytes = entry->bytes;
+
+	if (bits)
+		*bits = entry->nbits;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(nvmem_cell_get_size);
+
 static int nvmem_cell_read_common(struct device *dev, const char *cell_id,
 				  void *val, size_t count)
 {
diff --git a/include/linux/nvmem-consumer.h b/include/linux/nvmem-consumer.h
index 34c0e58dfa26..bcb0e17e415d 100644
--- a/include/linux/nvmem-consumer.h
+++ b/include/linux/nvmem-consumer.h
@@ -56,6 +56,7 @@ void nvmem_cell_put(struct nvmem_cell *cell);
 void devm_nvmem_cell_put(struct device *dev, struct nvmem_cell *cell);
 void *nvmem_cell_read(struct nvmem_cell *cell, size_t *len);
 int nvmem_cell_write(struct nvmem_cell *cell, void *buf, size_t len);
+int nvmem_cell_get_size(struct nvmem_cell *cell, size_t *bytes, size_t *bits);
 int nvmem_cell_read_u8(struct device *dev, const char *cell_id, u8 *val);
 int nvmem_cell_read_u16(struct device *dev, const char *cell_id, u16 *val);
 int nvmem_cell_read_u32(struct device *dev, const char *cell_id, u32 *val);
@@ -128,6 +129,12 @@ static inline int nvmem_cell_write(struct nvmem_cell *cell,
 	return -EOPNOTSUPP;
 }
 
+static inline int nvmem_cell_get_size(struct nvmem_cell *cell, size_t *bytes,
+				      size_t *bits)
+{
+	return -EOPNOTSUPP;
+}
+
 static inline int nvmem_cell_read_u8(struct device *dev,
 				     const char *cell_id, u8 *val)
 {

-- 
2.34.1

[PATCH v2 4/4] arm64: dts: qcom: lemans: Add PSCRR NVMEM recorder node

[Faruque Ansari]

Add a one-byte NVMEM cell node  in the SDAM to persist the power
state change reason across resets, and wire it to a pscrr-nvmem
recorder consumer node so the reason is recorded before
shutdown/reboot and read back on the next boot.

Signed-off-by: Faruque Ansari <faruque.ansari@oss.qualcomm.com>
---
 arch/arm64/boot/dts/qcom/lemans-pmics.dtsi | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/arch/arm64/boot/dts/qcom/lemans-pmics.dtsi b/arch/arm64/boot/dts/qcom/lemans-pmics.dtsi
index 500f715931aa..96db3f57969f 100644
--- a/arch/arm64/boot/dts/qcom/lemans-pmics.dtsi
+++ b/arch/arm64/boot/dts/qcom/lemans-pmics.dtsi
@@ -97,6 +97,12 @@ reboot-mode {
 		mode-recovery = <0x01>;
 		mode-bootloader = <0x02>;
 	};
+
+	reboot-reason {
+		compatible = "pscrr-nvmem";
+		nvmem-cells = <&reboot_reason_persist>;
+		nvmem-cell-names = "pscr";
+	};
 };
 
 &spmi_bus {
@@ -186,6 +192,16 @@ reboot_reason: reboot-reason@48 {
 				reg = <0x48 0x1>;
 				bits = <1 7>;
 			};
+
+			nvmem-layout {
+				compatible = "fixed-layout";
+				#address-cells = <1>;
+				#size-cells = <1>;
+
+				reboot_reason_persist: reboot-reason-persist@49 {
+					reg = <0x49 0x1>;
+				};
+			};
 		};
 	};
 

-- 
2.34.1

Re: [PATCH v2 4/4] arm64: dts: qcom: lemans: Add PSCRR NVMEM recorder node

[Abel Vesa]

On 26-08-19 22:50:46, Faruque Ansari wrote:
> Add a one-byte NVMEM cell node  in the SDAM to persist the power

Super nit: If you respin, drop the extra space between node and in.

> state change reason across resets, and wire it to a pscrr-nvmem
> recorder consumer node so the reason is recorded before
> shutdown/reboot and read back on the next boot.
> 
> Signed-off-by: Faruque Ansari <faruque.ansari@oss.qualcomm.com>

Reviewed-by: Abel Vesa <abel.vesa@oss.qualcomm.com>

Re: [PATCH v2 4/4] arm64: dts: qcom: lemans: Add PSCRR NVMEM recorder node

[Faruque Ansari]

Hi Abel Vesa,

On 20-Aug-26 12:25 AM, Abel Vesa wrote:
> On 26-08-19 22:50:46, Faruque Ansari wrote:
>> Add a one-byte NVMEM cell node  in the SDAM to persist the power
> 
> Super nit: If you respin, drop the extra space between node and in.

Thanks for the review.
I'll fix this in V3.

Thanks
Faruque Ansari>
>> state change reason across resets, and wire it to a pscrr-nvmem
>> recorder consumer node so the reason is recorded before
>> shutdown/reboot and read back on the next boot.
>>
>> Signed-off-by: Faruque Ansari <faruque.ansari@oss.qualcomm.com>
> 
> Reviewed-by: Abel Vesa <abel.vesa@oss.qualcomm.com>

Re: [PATCH v2 1/4] dt-bindings: power: reset: add PSCRR NVMEM recorder binding

[Krzysztof Kozlowski]

On Wed, Aug 19, 2026 at 10:50:43PM +0530, Faruque Ansari wrote:
> Add binding for the PSCRR NVMEM recorder. Records the power state
> change reason into a small NVMEM cell, such as a PMIC SDAM byte or
> RTC scratch register — so the cause survives a power cycle and can be
> read back on the next boot.

A nit, subject: drop second/last, redundant "binding". The
"dt-bindings" prefix is already stating that these are bindings.
See also:
https://elixir.bootlin.com/linux/v7.1-rc7/source/Documentation/devicetree/bindings/submitting-patches.rst#L23

> 
> Signed-off-by: Faruque Ansari <faruque.ansari@oss.qualcomm.com>
> ---
>  .../bindings/power/reset/pscrr-nvmem.yaml          | 59 ++++++++++++++++++++++
>  MAINTAINERS                                        |  1 +
>  2 files changed, 60 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/power/reset/pscrr-nvmem.yaml b/Documentation/devicetree/bindings/power/reset/pscrr-nvmem.yaml
> new file mode 100644
> index 000000000000..5334c923d644
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/power/reset/pscrr-nvmem.yaml
> @@ -0,0 +1,59 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/power/reset/pscrr-nvmem.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: NVMEM Power State Change Reason recorder
> +
> +maintainers:
> +  - Faruque Ansari <faruque.ansari@oss.qualcomm.com>
> +  - Oleksij Rempel <o.rempel@pengutronix.de>
> +
> +description:
> +  An NVMEM-backed recorder for Power State Change Reasons (PSCRR). Persists
> +  the reboot or shutdown cause into a small NVMEM cell, such as an RTC
> +  scratch register, a PMIC SDAM (Scratch Data Access Memory) byte, or an
> +  EEPROM — so the reason survives a power cycle and can be read back on the
> +  next boot. The cell is referenced via the standard nvmem-cells consumer
> +  binding.

I do not see how this should be a separate device. This should be rather part
of PSCRR, reboot handler or just the nvmem. Otherwise it is just device
node for instantiating driver.

Best regards,
Krzysztof