Re: [PATCH 2/3] power: reset: add MCF5441x RCM power-on reason driver

[Sebastian Reichel <sebastian.reichel@collabora.com>]

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Hi,

On Tue, Jun 02, 2026 at 11:21:22AM +0200, Jean-Michel Hautbois wrote:
> 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.
> 
> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@yoseli.org>
> ---
>  MAINTAINERS                         |   6 ++
>  drivers/power/reset/Kconfig         |  12 ++++
>  drivers/power/reset/Makefile        |   1 +
>  drivers/power/reset/mcf-rcm-reset.c | 109 ++++++++++++++++++++++++++++++++++++
>  4 files changed, 128 insertions(+)
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 461a3eed6129..1109bff23ec1 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -10195,6 +10195,12 @@ S:	Maintained
>  F:	drivers/mmc/host/sdhci-esdhc-mcf.c
>  F:	include/linux/platform_data/mmc-esdhc-mcf.h
>  
> +FREESCALE COLDFIRE M5441X RCM POWER-ON REASON DRIVER
> +M:	Jean-Michel Hautbois <jeanmichel.hautbois@yoseli.org>
> +L:	linux-m68k@lists.linux-m68k.org
> +S:	Maintained
> +F:	drivers/power/reset/mcf-rcm-reset.c
> +
>  FREESCALE DIU FRAMEBUFFER DRIVER
>  M:	Timur Tabi <timur@kernel.org>
>  L:	linux-fbdev@vger.kernel.org
> diff --git a/drivers/power/reset/Kconfig b/drivers/power/reset/Kconfig
> index 124afb99febe..003638f652fa 100644
> --- a/drivers/power/reset/Kconfig
> +++ b/drivers/power/reset/Kconfig
> @@ -128,6 +128,18 @@ config POWER_RESET_LINKSTATION
>  
>  	  Say Y here if you have a Buffalo LinkStation LS421D/E.
>  
> +config POWER_RESET_MCF_RCM
> +	tristate "Freescale ColdFire RCM power-on reason driver"
> +	depends on M5441x

If you describe the register layout in the driver, you
could add "|| COMPILE_TEST" resulting in much better
test coverage.

> +	depends on HAS_IOMEM
> +	help
> +	  This driver exposes the cause of the last reset on Freescale
> +	  ColdFire 5441x SoCs through the standard power_on_reason sysfs
> +	  ABI. It reads the Reset Status Register (RSR) of the Reset
> +	  Controller Module once at probe time and reports a normalised
> +	  string (regular power-up, reset button action, software reset
> +	  or unknown reason).
> +
>  config POWER_RESET_MACSMC
>  	tristate "Apple SMC reset/power-off driver"
>  	depends on MFD_MACSMC
> diff --git a/drivers/power/reset/Makefile b/drivers/power/reset/Makefile
> index d7ae97241a83..e31cab4ba78e 100644
> --- a/drivers/power/reset/Makefile
> +++ b/drivers/power/reset/Makefile
> @@ -13,6 +13,7 @@ obj-$(CONFIG_POWER_RESET_GPIO) += gpio-poweroff.o
>  obj-$(CONFIG_POWER_RESET_GPIO_RESTART) += gpio-restart.o
>  obj-$(CONFIG_POWER_RESET_HISI) += hisi-reboot.o
>  obj-$(CONFIG_POWER_RESET_LINKSTATION) += linkstation-poweroff.o
> +obj-$(CONFIG_POWER_RESET_MCF_RCM) += mcf-rcm-reset.o
>  obj-$(CONFIG_POWER_RESET_MACSMC) += macsmc-reboot.o
>  obj-$(CONFIG_POWER_RESET_MSM) += msm-poweroff.o
>  obj-$(CONFIG_POWER_RESET_MT6323) += mt6323-poweroff.o
> diff --git a/drivers/power/reset/mcf-rcm-reset.c b/drivers/power/reset/mcf-rcm-reset.c
> new file mode 100644
> index 000000000000..666ae1455be1
> --- /dev/null
> +++ b/drivers/power/reset/mcf-rcm-reset.c
> @@ -0,0 +1,109 @@
> +// 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/module.h>
> +#include <linux/platform_device.h>
> +#include <linux/power/power_on_reason.h>
> +
> +#include <asm/m5441xsim.h>
> +
> +#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", 0, },
    { }
};
MODULE_DEVICE_TABLE(platform, mcf_rcm_id);

> +static struct platform_driver mcf_rcm_driver = {
> +	.probe = mcf_rcm_probe,
> +	.driver = {
> +		.name = "mcf-rcm-reset",
> +		.dev_groups = mcf_rcm_groups,
> +	},

.id_table = mcf_rcm_id,

> +};
> +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");
> +MODULE_ALIAS("platform:mcf-rcm-reset");

You can drop the MODULE_ALIAS with the platform ID table being
done properly.

Otherwise LGTM.

-- Sebastian

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