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Add a driver that decodes the Reset Status Register (RSR) of the Freescale ColdFire MCF5441x Reset Controller Module at probe time and exposes the cause via the power_on_reason sysfs ABI. The RSR can latch several cause bits simultaneously (Reference Manual chapter 12.3.2); the driver picks one cause per a priority that favours the most explanatory diagnostic. The register layout is described in the driver so it can be built with COMPILE_TEST on any architecture. Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@yoseli.org> Link: https://patch.msgid.link/20260617-coldfire-rcm-power-on-reason-v3-1-1a7c7b6b14e7@yoseli.org Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
127 lines
3.7 KiB
C
127 lines
3.7 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Freescale ColdFire MCF5441x RCM power-on reason driver
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*
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* Copyright (C) 2026 Jean-Michel Hautbois <jeanmichel.hautbois@yoseli.org>
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*/
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#include <linux/io.h>
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#include <linux/mod_devicetable.h>
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#include <linux/module.h>
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#include <linux/platform_device.h>
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#include <linux/power/power_on_reason.h>
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/*
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* Reset Status Register (RSR) layout, MCF54418 Reference Manual chapter
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* 12.3.2. The register is 8-bit read-only and latches the cause (or
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* causes) of the most recent reset until the next one occurs.
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*/
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#define MCF_RSR_SOFT 0x20 /* Last reset caused by software */
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#define MCF_RSR_LOC 0x10 /* Last reset caused by PLL loss of clock */
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#define MCF_RSR_POR 0x08 /* Last reset caused by power-on */
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#define MCF_RSR_EXT 0x04 /* Last reset caused by external pin */
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#define MCF_RSR_WDRCORE 0x02 /* Last reset caused by core watchdog */
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#define MCF_RSR_LOL 0x01 /* Last reset caused by PLL loss of lock */
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#define MCF_RSR_KNOWN_CAUSES (MCF_RSR_POR | MCF_RSR_EXT | MCF_RSR_WDRCORE | \
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MCF_RSR_LOC | MCF_RSR_LOL | MCF_RSR_SOFT)
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struct mcf_rcm {
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const char *reason;
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};
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/*
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* Decode RSR into a power_on_reason string.
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*
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* The MCF5441x Reset Status Register can latch several cause bits at the
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* same time (Reference Manual chapter 12.3.2: "one or more status bits
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* may be set at the same time"). A power-on, for example, also resets
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* the PLL and may co-flag LOC and LOL during the boot sequence. The
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* power_on_reason ABI carries a single string, so this routine picks
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* one cause; the chosen priority surfaces the most explanatory one for
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* diagnostics:
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*
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* POR cold boot dominates any spurious co-flagged cause
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* EXT operator action via the RESET pin
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* WDRCORE core watchdog timeout, a fault to investigate
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* LOC, LOL PLL clock or lock failure, hardware fault
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* SOFT explicit software-requested reset
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*/
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static const char *mcf_rcm_decode(u8 rsr)
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{
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if (rsr & MCF_RSR_POR)
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return POWER_ON_REASON_REGULAR;
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if (rsr & MCF_RSR_EXT)
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return POWER_ON_REASON_RST_BTN;
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if (rsr & MCF_RSR_WDRCORE)
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return POWER_ON_REASON_WATCHDOG;
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if (rsr & (MCF_RSR_LOC | MCF_RSR_LOL))
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return POWER_ON_REASON_CPU_CLK_FAIL;
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if (rsr & MCF_RSR_SOFT)
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return POWER_ON_REASON_SOFTWARE;
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return POWER_ON_REASON_UNKNOWN;
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}
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static ssize_t power_on_reason_show(struct device *dev,
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struct device_attribute *attr, char *buf)
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{
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struct mcf_rcm *rcm = platform_get_drvdata(to_platform_device(dev));
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return sysfs_emit(buf, "%s\n", rcm->reason);
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}
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static DEVICE_ATTR_RO(power_on_reason);
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static struct attribute *mcf_rcm_attrs[] = {
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&dev_attr_power_on_reason.attr,
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NULL,
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};
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ATTRIBUTE_GROUPS(mcf_rcm);
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static int mcf_rcm_probe(struct platform_device *pdev)
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{
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struct mcf_rcm *rcm;
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void __iomem *base;
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u8 rsr;
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rcm = devm_kzalloc(&pdev->dev, sizeof(*rcm), GFP_KERNEL);
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if (!rcm)
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return -ENOMEM;
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base = devm_platform_ioremap_resource(pdev, 0);
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if (IS_ERR(base))
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return PTR_ERR(base);
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rsr = readb_relaxed(base);
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rcm->reason = mcf_rcm_decode(rsr);
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platform_set_drvdata(pdev, rcm);
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if (!(rsr & MCF_RSR_KNOWN_CAUSES))
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dev_warn(&pdev->dev, "Unknown reset cause (RSR=0x%02x)\n", rsr);
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else
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dev_info(&pdev->dev, "Starting after %s (RSR=0x%02x)\n",
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rcm->reason, rsr);
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return 0;
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}
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static const struct platform_device_id mcf_rcm_id[] = {
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{ "mcf-rcm-reset" },
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{ }
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};
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MODULE_DEVICE_TABLE(platform, mcf_rcm_id);
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static struct platform_driver mcf_rcm_driver = {
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.probe = mcf_rcm_probe,
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.id_table = mcf_rcm_id,
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.driver = {
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.name = "mcf-rcm-reset",
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.dev_groups = mcf_rcm_groups,
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},
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};
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module_platform_driver(mcf_rcm_driver);
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MODULE_AUTHOR("Jean-Michel Hautbois <jeanmichel.hautbois@yoseli.org>");
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MODULE_DESCRIPTION("Freescale ColdFire RCM power-on reason driver");
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MODULE_LICENSE("GPL");
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