drivers/power/reset/mcf-rcm-reset.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Freescale ColdFire MCF5441x RCM power-on reason driver
 *
 * Copyright (C) 2026 Jean-Michel Hautbois <jeanmichel.hautbois@yoseli.org>
 */

#include <linux/io.h>
#include <linux/mod_devicetable.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/power/power_on_reason.h>

/*
 * Reset Status Register (RSR) layout, MCF54418 Reference Manual chapter
 * 12.3.2. The register is 8-bit read-only and latches the cause (or
 * causes) of the most recent reset until the next one occurs.
 */
#define MCF_RSR_SOFT		0x20	/* Last reset caused by software */
#define MCF_RSR_LOC		0x10	/* Last reset caused by PLL loss of clock */
#define MCF_RSR_POR		0x08	/* Last reset caused by power-on */
#define MCF_RSR_EXT		0x04	/* Last reset caused by external pin */
#define MCF_RSR_WDRCORE		0x02	/* Last reset caused by core watchdog */
#define MCF_RSR_LOL		0x01	/* Last reset caused by PLL loss of lock */

#define MCF_RSR_KNOWN_CAUSES	(MCF_RSR_POR | MCF_RSR_EXT | MCF_RSR_WDRCORE | \
				 MCF_RSR_LOC | MCF_RSR_LOL | MCF_RSR_SOFT)

struct mcf_rcm {
	const char *reason;
};

/*
 * Decode RSR into a power_on_reason string.
 *
 * The MCF5441x Reset Status Register can latch several cause bits at the
 * same time (Reference Manual chapter 12.3.2: "one or more status bits
 * may be set at the same time"). A power-on, for example, also resets
 * the PLL and may co-flag LOC and LOL during the boot sequence. The
 * power_on_reason ABI carries a single string, so this routine picks
 * one cause; the chosen priority surfaces the most explanatory one for
 * diagnostics:
 *
 *   POR              cold boot dominates any spurious co-flagged cause
 *   EXT              operator action via the RESET pin
 *   WDRCORE          core watchdog timeout, a fault to investigate
 *   LOC, LOL         PLL clock or lock failure, hardware fault
 *   SOFT             explicit software-requested reset
 */
static const char *mcf_rcm_decode(u8 rsr)
{
	if (rsr & MCF_RSR_POR)
		return POWER_ON_REASON_REGULAR;
	if (rsr & MCF_RSR_EXT)
		return POWER_ON_REASON_RST_BTN;
	if (rsr & MCF_RSR_WDRCORE)
		return POWER_ON_REASON_WATCHDOG;
	if (rsr & (MCF_RSR_LOC | MCF_RSR_LOL))
		return POWER_ON_REASON_CPU_CLK_FAIL;
	if (rsr & MCF_RSR_SOFT)
		return POWER_ON_REASON_SOFTWARE;
	return POWER_ON_REASON_UNKNOWN;
}

static ssize_t power_on_reason_show(struct device *dev,
				    struct device_attribute *attr, char *buf)
{
	struct mcf_rcm *rcm = platform_get_drvdata(to_platform_device(dev));

	return sysfs_emit(buf, "%s\n", rcm->reason);
}
static DEVICE_ATTR_RO(power_on_reason);

static struct attribute *mcf_rcm_attrs[] = {
	&dev_attr_power_on_reason.attr,
	NULL,
};
ATTRIBUTE_GROUPS(mcf_rcm);

static int mcf_rcm_probe(struct platform_device *pdev)
{
	struct mcf_rcm *rcm;
	void __iomem *base;
	u8 rsr;

	rcm = devm_kzalloc(&pdev->dev, sizeof(*rcm), GFP_KERNEL);
	if (!rcm)
		return -ENOMEM;

	base = devm_platform_ioremap_resource(pdev, 0);
	if (IS_ERR(base))
		return PTR_ERR(base);

	rsr = readb_relaxed(base);
	rcm->reason = mcf_rcm_decode(rsr);

	platform_set_drvdata(pdev, rcm);

	if (!(rsr & MCF_RSR_KNOWN_CAUSES))
		dev_warn(&pdev->dev, "Unknown reset cause (RSR=0x%02x)\n", rsr);
	else
		dev_info(&pdev->dev, "Starting after %s (RSR=0x%02x)\n",
			 rcm->reason, rsr);

	return 0;
}

static const struct platform_device_id mcf_rcm_id[] = {
	{ "mcf-rcm-reset" },
	{ }
};
MODULE_DEVICE_TABLE(platform, mcf_rcm_id);

static struct platform_driver mcf_rcm_driver = {
	.probe = mcf_rcm_probe,
	.id_table = mcf_rcm_id,
	.driver = {
		.name = "mcf-rcm-reset",
		.dev_groups = mcf_rcm_groups,
	},
};
module_platform_driver(mcf_rcm_driver);

MODULE_AUTHOR("Jean-Michel Hautbois <jeanmichel.hautbois@yoseli.org>");
MODULE_DESCRIPTION("Freescale ColdFire RCM power-on reason driver");
MODULE_LICENSE("GPL");