Message-Id: <20250304132433.210355-6-o.rempel@pengutronix.de>
Date: Tue,  4 Mar 2025 14:24:31 +0100
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: Sebastian Reichel <sre@...nel.org>,
	Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
Cc: Oleksij Rempel <o.rempel@...gutronix.de>,
	kernel@...gutronix.de,
	linux-kernel@...r.kernel.org,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Zhang Rui <rui.zhang@...el.com>,
	Lukasz Luba <lukasz.luba@....com>,
	linux-pm@...r.kernel.org,
	Søren Andersen <san@...v.dk>
Subject: [PATCH v3 5/7] power: reset: add PSCR NVMEM Driver for Recording Power State Change Reasons

This driver utilizes the Power State Change Reasons Recording (PSCRR)
framework to store specific power state change information, such as
shutdown or reboot reasons, into a designated non-volatile memory
(NVMEM) cell.

Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
---
 drivers/power/reset/Kconfig       |  11 ++
 drivers/power/reset/Makefile      |   1 +
 drivers/power/reset/pscrr-nvmem.c | 254 ++++++++++++++++++++++++++++++
 3 files changed, 266 insertions(+)
 create mode 100644 drivers/power/reset/pscrr-nvmem.c

diff --git a/drivers/power/reset/Kconfig b/drivers/power/reset/Kconfig
index 0f6aee415f1c..de7bae1b3be3 100644
--- a/drivers/power/reset/Kconfig
+++ b/drivers/power/reset/Kconfig
@@ -335,3 +335,14 @@ menuconfig PSCRR
       timeouts.
 
       If unsure, say N.
+
+if PSCRR
+
+config PSCRR_NVMEM
+	tristate "Generic NVMEM-based Power State Change Reason Recorder"
+	depends on OF
+	help
+	  Enabling this option adds support for recording power state change
+	  reasons in a NVMEM cell.
+
+endif
diff --git a/drivers/power/reset/Makefile b/drivers/power/reset/Makefile
index dbd6ae6b26a4..532698552d40 100644
--- a/drivers/power/reset/Makefile
+++ b/drivers/power/reset/Makefile
@@ -33,6 +33,7 @@ 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.o
+obj-$(CONFIG_PSCRR_NVMEM) += pscrr-nvmem.o
 obj-$(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-nvmem.c b/drivers/power/reset/pscrr-nvmem.c
new file mode 100644
index 000000000000..c6912a1a4f7b
--- /dev/null
+++ b/drivers/power/reset/pscrr-nvmem.c
@@ -0,0 +1,254 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * pscrr_nvmem.c - PSCRR backend for storing shutdown reasons in small NVMEM
+ *		   cells
+ *
+ * This backend provides a way to persist power state change reasons in a
+ * non-volatile memory (NVMEM) cell, ensuring that reboot causes can be
+ * analyzed post-mortem. Unlike traditional logging to eMMC or NAND, which
+ * may be unreliable during power failures, this approach allows storing
+ * reboot reasons in small, fast-access storage like RTC scratchpads, EEPROM,
+ * or FRAM.
+ *
+ * The module allows dynamic configuration of the NVMEM device and cell
+ * via module parameters:
+ *
+ * Example usage:
+ *   modprobe pscrr-nvmem nvmem_name=pcf85063_nvram0 cell_name=pscr@0,0
+ */
+
+#include <linux/err.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/nvmem-consumer.h>
+#include <linux/pscrr.h>
+#include <linux/slab.h>
+
+/*
+ * Module parameters:
+ *   nvmem_name: Name of the NVMEM device (e.g. "pcf85063_nvram0").
+ *   cell_name : Sysfs name of the cell on that device (e.g. "pscr@0,0").
+ */
+static char *nvmem_name;
+module_param(nvmem_name, charp, 0444);
+MODULE_PARM_DESC(nvmem_name, "Name of the NVMEM device (e.g. pcf85063_nvram0)");
+
+static char *cell_name;
+module_param(cell_name, charp, 0444);
+MODULE_PARM_DESC(cell_name, "Sysfs name of the NVMEM cell (e.g. pscr@0,0)");
+
+struct pscrr_nvmem_priv {
+	struct nvmem_device *nvmem;
+	struct nvmem_cell *cell;
+
+	unsigned int total_bits;
+	size_t max_val;
+};
+
+static struct pscrr_nvmem_priv *priv;
+
+static int pscrr_nvmem_write_reason(enum pscr_reason reason)
+{
+	size_t required_bytes;
+	u32 val;
+	int ret;
+
+	if (!priv || !priv->cell)
+		return -ENODEV;
+
+	/* Ensure reason fits in the available storage */
+	if (reason > priv->max_val) {
+		pr_err("PSCRR-nvmem: Reason %d exceeds max storable value %zu for %u-bit cell\n",
+		       reason, priv->max_val, priv->total_bits);
+		return -ERANGE;
+	}
+
+	val = reason;
+
+	/* Determine required bytes for storing total_bits */
+	required_bytes = (priv->total_bits + 7) / 8;
+
+	/* Write the reason to the NVMEM cell */
+	ret = nvmem_cell_write(priv->cell, &val, required_bytes);
+	if (ret < 0) {
+		pr_err("PSCRR-nvmem: Failed to write reason %d, err=%d (%pe)\n",
+		       reason, ret, ERR_PTR(ret));
+		return ret;
+	}
+
+	pr_debug("PSCRR-nvmem: Successfully wrote reason %d\n", reason);
+
+	return 0;
+}
+
+static int pscrr_nvmem_read_reason(enum pscr_reason *reason)
+{
+	unsigned int required_bytes, val;
+	int ret = 0;
+	size_t len;
+	void *buf;
+
+	if (!priv || !priv->cell)
+		return -ENODEV;
+
+	buf = nvmem_cell_read(priv->cell, &len);
+	if (IS_ERR(buf)) {
+		ret = PTR_ERR(buf);
+		pr_err("PSCRR-nvmem: Failed to read cell, err=%d (%pe)\n", ret,
+		       ERR_PTR(ret));
+		return ret;
+	}
+
+	/* Calculate the required number of bytes */
+	required_bytes = (priv->total_bits + 7) / 8;
+
+	/* Validate that the returned length is large enough */
+	if (len < required_bytes) {
+		pr_err("PSCRR-nvmem: Read length %zu is too small (need at least %u bytes)\n",
+		       len, required_bytes);
+		kfree(buf);
+		return -EIO;
+	}
+
+	/* Extract value safely with proper memory alignment handling */
+	val = 0;
+	memcpy(&val, buf, required_bytes);
+
+	/* Mask only the necessary bits to avoid garbage data */
+	val &= (1U << priv->total_bits) - 1;
+
+	kfree(buf);
+
+	*reason = (enum pscr_reason)val;
+
+	pr_debug("PSCRR-nvmem: Read reason => %d (from %zu bytes, %u bits used)\n",
+		 *reason, len, priv->total_bits);
+
+	return 0;
+}
+
+static const struct pscrr_backend_ops pscrr_nvmem_ops = {
+	.write_reason = pscrr_nvmem_write_reason,
+	.read_reason  = pscrr_nvmem_read_reason,
+};
+
+static int __init pscrr_nvmem_init(void)
+{
+	size_t bytes, bits;
+	int ret;
+
+	if (!nvmem_name || !cell_name) {
+		pr_err("PSCRR-nvmem: Must specify both nvmem_name and cell_name.\n");
+		return -EINVAL;
+	}
+
+	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->nvmem = nvmem_device_get_by_name(nvmem_name);
+	if (IS_ERR(priv->nvmem)) {
+		ret = PTR_ERR(priv->nvmem);
+		pr_err("PSCRR-nvmem: nvmem_device_get_by_name(%s) failed: %d\n",
+		       nvmem_name, ret);
+		priv->nvmem = NULL;
+		goto err_free;
+	}
+
+	priv->cell = nvmem_cell_get_by_sysfs_name(priv->nvmem, cell_name);
+	if (IS_ERR(priv->cell)) {
+		ret = PTR_ERR(priv->cell);
+		pr_err("PSCRR-nvmem: nvmem_cell_get_by_sysfs_name(%s) failed, err=%pe\n",
+		       cell_name, ERR_PTR(ret));
+		priv->cell = NULL;
+		goto err_dev_put;
+	}
+
+	ret = nvmem_cell_get_size(priv->cell, &bytes, &bits);
+	if (ret < 0) {
+		pr_err("PSCRR-nvmem: Failed to get cell size, err=%pe\n",
+		       ERR_PTR(ret));
+		goto err_cell_put;
+	}
+
+	if (bits)
+		priv->total_bits = bits;
+	else
+		priv->total_bits = bytes * 8;
+
+	if (priv->total_bits > 31) {
+		pr_err("PSCRR-nvmem: total_bits=%u is too large (max 31 allowed)\n",
+		       priv->total_bits);
+		return -EOVERFLOW;
+	}
+
+	priv->max_val = (1 << priv->total_bits) - 1;
+	pr_debug("PSCRR-nvmem: Cell size: %zu bytes + %zu bits => total_bits=%u\n",
+		 bytes, bits, priv->total_bits);
+
+	/*
+	 * If we store reasons 0..PSCR_MAX_REASON, the largest needed is
+	 * 'PSCR_MAX_REASON'. That must fit within total_bits.
+	 * So the max storable integer is (1 << total_bits) - 1.
+	 */
+	if (priv->max_val < PSCR_MAX_REASON) {
+		pr_err("PSCRR-nvmem: Not enough bits (%u) to store up to reason=%d\n",
+		       priv->total_bits, PSCR_MAX_REASON);
+		ret = -ENOSPC;
+		goto err_cell_put;
+	}
+
+	/* 4. Register with pscrr_core. */
+	ret = pscrr_core_init(&pscrr_nvmem_ops);
+	if (ret) {
+		pr_err("PSCRR-nvmem: pscrr_core_init() failed: %d\n", ret);
+		goto err_cell_put;
+	}
+
+	pr_info("PSCRR-nvmem: Loaded (nvmem=%s, cell=%s), can store 0..%zu\n",
+		nvmem_name, cell_name, priv->max_val);
+	return 0;
+
+err_cell_put:
+	if (priv->cell) {
+		nvmem_cell_put(priv->cell);
+		priv->cell = NULL;
+	}
+err_dev_put:
+	if (priv->nvmem) {
+		nvmem_device_put(priv->nvmem);
+		priv->nvmem = NULL;
+	}
+err_free:
+	kfree(priv);
+	priv = NULL;
+	return ret;
+}
+
+static void __exit pscrr_nvmem_exit(void)
+{
+	pscrr_core_exit();
+
+	if (priv) {
+		if (priv->cell) {
+			nvmem_cell_put(priv->cell);
+			priv->cell = NULL;
+		}
+		if (priv->nvmem) {
+			nvmem_device_put(priv->nvmem);
+			priv->nvmem = NULL;
+		}
+		kfree(priv);
+		priv = NULL;
+	}
+
+	pr_info("pscrr-nvmem: Unloaded\n");
+}
+
+module_init(pscrr_nvmem_init);
+module_exit(pscrr_nvmem_exit);
+
+MODULE_AUTHOR("Oleksij Rempel <o.rempel@...gutronix.de>");
+MODULE_DESCRIPTION("PSCRR backend for storing reason code in NVMEM");
+MODULE_LICENSE("GPL");
-- 
2.39.5

Powered by blists - more mailing lists