Re: [PATCH 2/2] thermal: qcom: add PM8901 PMIC temperature-alarm driver

[Dmitry Baryshkov]

On Sat, May 30, 2026 at 04:00:40PM +0200, Herman van Hazendonk wrote:
> Add a thermal-of sensor driver for the temperature-alarm block inside
> the Qualcomm PM8901 PMIC. PM8901 is a secondary PMIC paired with
> PM8058 on the MSM8x60 family (MSM8260/MSM8660/APQ8060). It exposes
> an over-temperature alarm at SSBI offset 0x23/0x24 with three
> escalating stages (105/125/145 C); the driver decodes the stage +
> threshold pair into a millicelsius reading and registers two PMIC-
> internal interrupts (TEMP_ALARM at block 6 bit 4, TEMP_HI_ALARM at
> block 6 bit 5).
> 
> Used by board thermal-zones for the orderly_poweroff path on the HP
> TouchPad.
> 
> Signed-off-by: Herman van Hazendonk <github.com@xxxxxxxxxx>
> ---
>  drivers/thermal/qcom/Kconfig          |  12 +
>  drivers/thermal/qcom/Makefile         |   1 +
>  drivers/thermal/qcom/qcom-pm8901-tm.c | 341 ++++++++++++++++++++++++++
>  3 files changed, 354 insertions(+)
>  create mode 100644 drivers/thermal/qcom/qcom-pm8901-tm.c
> 
> diff --git a/drivers/thermal/qcom/Kconfig b/drivers/thermal/qcom/Kconfig
> index a6bb01082ec6..af099032f1e6 100644
> --- a/drivers/thermal/qcom/Kconfig
> +++ b/drivers/thermal/qcom/Kconfig
> @@ -32,6 +32,18 @@ config QCOM_SPMI_TEMP_ALARM
>  	  real time die temperature if an ADC is present or an estimate of the
>  	  temperature based upon the over temperature stage value.
>  
> +config QCOM_PM8901_TEMP_ALARM
> +	tristate "Qualcomm PM8901 PMIC Temperature Alarm"
> +	depends on MFD_PM8XXX || COMPILE_TEST
> +	depends on THERMAL_OF
> +	help
> +	  This enables the thermal driver for the PM8901 PMIC over-temperature
> +	  alarm block. PM8901 exposes a stage-based alarm (no raw ADC) with
> +	  four selectable thresholds and three escalating stages. The driver
> +	  registers a thermal-of sensor so a board device tree can declare
> +	  trip points and a critical-trip action (orderly_poweroff). Used on
> +	  HP TouchPad (APQ8060) where PM8901 supplies the secondary PMIC die.
> +
>  config QCOM_LMH
>  	tristate "Qualcomm Limits Management Hardware"
>  	depends on ARCH_QCOM || COMPILE_TEST
> diff --git a/drivers/thermal/qcom/Makefile b/drivers/thermal/qcom/Makefile
> index 0fa2512042e7..90dc05151e33 100644
> --- a/drivers/thermal/qcom/Makefile
> +++ b/drivers/thermal/qcom/Makefile
> @@ -5,4 +5,5 @@ qcom_tsens-y			+= tsens.o tsens-v2.o tsens-v1.o tsens-v0_1.o \
>  				   tsens-8960.o
>  obj-$(CONFIG_QCOM_SPMI_ADC_TM5)	+= qcom-spmi-adc-tm5.o
>  obj-$(CONFIG_QCOM_SPMI_TEMP_ALARM)	+= qcom-spmi-temp-alarm.o
> +obj-$(CONFIG_QCOM_PM8901_TEMP_ALARM)	+= qcom-pm8901-tm.o
>  obj-$(CONFIG_QCOM_LMH)		+= lmh.o
> diff --git a/drivers/thermal/qcom/qcom-pm8901-tm.c b/drivers/thermal/qcom/qcom-pm8901-tm.c
> new file mode 100644
> index 000000000000..d174d6897921
> --- /dev/null
> +++ b/drivers/thermal/qcom/qcom-pm8901-tm.c
> @@ -0,0 +1,341 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Qualcomm PM8901 PMIC Thermal-Alarm Driver
> + *
> + * Mainline port of the legacy 2.6.35-palm drivers/thermal/pmic8901-tm.c.
> + * PM8901 exposes a stage-based over-temperature alarm (no raw ADC) with
> + * four selectable thresholds and three escalating stages. This driver
> + * mirrors the legacy programming exactly (threshold-set 0, software
> + * override enabled, PWM gating at 8 Hz) and registers a thermal-of
> + * sensor so a board DT can declare trip points and a critical action.
> + *
> + * Copyright (c) 2010-2011, Code Aurora Forum.
> + * Copyright (c) 2026, HP TouchPad mainline port.
> + */
> +
> +#include <linux/bitfield.h>
> +#include <linux/bitops.h>
> +#include <linux/interrupt.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/of.h>
> +#include <linux/platform_device.h>
> +#include <linux/regmap.h>
> +#include <linux/thermal.h>
> +
> +/* SSBI registers (offsets from the per-instance reg base) */
> +#define PM8901_TM_REG_CTRL		0x00	/* CTRL/STATUS  (base + 0) */
> +#define PM8901_TM_REG_PWM		0x01	/* PWM gating  (base + 1) */
> +
> +/* CTRL register fields */
> +#define CTRL_ST3_SD			BIT(7)
> +#define CTRL_ST2_SD			BIT(6)
> +#define CTRL_STATUS_MASK		GENMASK(5, 4)
> +#define CTRL_THRESH_MASK		GENMASK(3, 2)
> +#define CTRL_OVRD_ST3			BIT(1)
> +#define CTRL_OVRD_ST2			BIT(0)
> +#define CTRL_OVRD_MASK			GENMASK(1, 0)
> +
> +/* PWM register fields */
> +#define PWM_EN				BIT(7)
> +#define PWM_PER_PRE_MASK		GENMASK(5, 3)
> +#define PWM_PER_DIV_MASK		GENMASK(2, 0)
> +
> +/* Temperature math (from legacy pmic8901-tm.c) */
> +#define PM8901_TEMP_STAGE_STEP		20000	/* 20 deg C between stages */
> +#define PM8901_TEMP_STAGE_HYSTERESIS	2000	/*  2 deg C transition guard */
> +#define PM8901_TEMP_THRESH_MIN		105000	/* threshold 0 base = 105 C */
> +#define PM8901_TEMP_THRESH_STEP		5000	/*  5 deg C per threshold step */
> +
> +/*
> + * PM8901 has no real die ADC; when stage == 0 ("below threshold") we
> + * report a plausible idle estimate matching the legacy DEFAULT_NO_ADC_TEMP.
> + */
> +#define PM8901_TEMP_NO_ALARM		37000
> +
> +struct pm8901_tm_chip {
> +	struct device			*dev;
> +	struct regmap			*map;
> +	struct thermal_zone_device	*tz_dev;
> +	struct mutex			lock;
> +	unsigned int			base;	/* SSBI offset, from DT reg */
> +	unsigned int			stage;
> +	unsigned int			thresh;
> +	int				temp;
> +	bool				initialised;
> +};
> +
> +static int pm8901_tm_read_ctrl(struct pm8901_tm_chip *chip, u8 *val)
> +{
> +	unsigned int v;
> +	int ret;
> +
> +	ret = regmap_read(chip->map, chip->base + PM8901_TM_REG_CTRL, &v);
> +	if (!ret)
> +		*val = v;
> +	return ret;
> +}
> +
> +static int pm8901_tm_write_ctrl(struct pm8901_tm_chip *chip, u8 val)
> +{
> +	return regmap_write(chip->map, chip->base + PM8901_TM_REG_CTRL, val);
> +}
> +
> +static int pm8901_tm_write_pwm(struct pm8901_tm_chip *chip, u8 val)
> +{
> +	return regmap_write(chip->map, chip->base + PM8901_TM_REG_PWM, val);
> +}

I'm personally not a fan of one-line wrappers (all three), but it's up
to you and the maintainers...

> +
> +/*
> + * Decode the (stage, threshold) pair into a single millicelsius value.
> + * Logic matches the legacy pmic8901-tm.c hysteresis selection:
> + *  - on a rising stage transition, use the lower bound of the new stage
> + *    plus +HYSTERESIS so we don't bounce
> + *  - on a falling stage transition, use the upper bound of the new stage
> + *    minus -HYSTERESIS
> + *  - on the first read after probe (initialised == false), pick a
> + *    representative point: midpoint of the stage range, or
> + *    PM8901_TEMP_NO_ALARM when stage == 0.
> + */
> +static int pm8901_tm_update_temp_locked(struct pm8901_tm_chip *chip)
> +{
> +	unsigned int new_stage;
> +	u8 reg;
> +	int ret;
> +
> +	ret = pm8901_tm_read_ctrl(chip, &reg);
> +	if (ret)
> +		return ret;
> +
> +	new_stage = FIELD_GET(CTRL_STATUS_MASK, reg);
> +	chip->thresh = FIELD_GET(CTRL_THRESH_MASK, reg);
> +
> +	if (!chip->initialised) {
> +		if (new_stage)
> +			chip->temp = PM8901_TEMP_THRESH_MIN +
> +				     chip->thresh * PM8901_TEMP_THRESH_STEP +
> +				     (new_stage - 1) * PM8901_TEMP_STAGE_STEP;
> +		else
> +			chip->temp = PM8901_TEMP_NO_ALARM;
> +		chip->initialised = true;
> +	} else if (new_stage > chip->stage) {
> +		chip->temp = PM8901_TEMP_THRESH_MIN +
> +			     chip->thresh * PM8901_TEMP_THRESH_STEP +
> +			     (new_stage - 1) * PM8901_TEMP_STAGE_STEP +
> +			     PM8901_TEMP_STAGE_HYSTERESIS;
> +	} else if (new_stage < chip->stage) {
> +		chip->temp = PM8901_TEMP_THRESH_MIN +
> +			     chip->thresh * PM8901_TEMP_THRESH_STEP +
> +			     new_stage * PM8901_TEMP_STAGE_STEP -
> +			     PM8901_TEMP_STAGE_HYSTERESIS;
> +	}
> +
> +	chip->stage = new_stage;
> +	return 0;
> +}
> +
> +static int pm8901_tm_get_temp(struct thermal_zone_device *tz, int *temp)
> +{
> +	struct pm8901_tm_chip *chip = thermal_zone_device_priv(tz);
> +	int ret;
> +
> +	if (!temp)
> +		return -EINVAL;
> +
> +	mutex_lock(&chip->lock);
> +	ret = pm8901_tm_update_temp_locked(chip);
> +	if (!ret)
> +		*temp = chip->temp;
> +	mutex_unlock(&chip->lock);
> +
> +	return ret;
> +}
> +
> +static const struct thermal_zone_device_ops pm8901_tm_zone_ops = {
> +	.get_temp = pm8901_tm_get_temp,

You don't have to implement it, but please add a comment. Are those
hardcoded?

> +};
> +
> +/*
> + * Program PM8901 to the legacy default: threshold-set 0 (105 / 125 / 145 C),

Any other options?

> + * software override enabled (kernel handles shutdown, PMIC does not auto-cut),
> + * PWM at 8 Hz (legacy "cut down on unnecessary interrupts" rate).
> + */
> +static int pm8901_tm_init_hw(struct pm8901_tm_chip *chip)
> +{
> +	int ret;
> +	u8 reg;
> +
> +	mutex_lock(&chip->lock);
> +
> +	ret = pm8901_tm_read_ctrl(chip, &reg);
> +	if (ret)
> +		goto out;
> +
> +	/*
> +	 * Enable software override so PMIC does NOT auto-shut-down on stage 3.
> +	 * Critical-trip orderly_poweroff is delivered by the kernel thermal
> +	 * core via the DT thermal-zone trip with type = "critical".
> +	 */
> +	reg = (reg & ~(CTRL_OVRD_MASK | CTRL_STATUS_MASK | CTRL_THRESH_MASK)) |
> +	      CTRL_OVRD_ST3 | CTRL_OVRD_ST2;
> +	ret = pm8901_tm_write_ctrl(chip, reg);
> +	if (ret)
> +		goto out;
> +
> +	chip->thresh = 0;
> +
> +	/* PWM @ 8 Hz: PWM_EN | PRE=3 | DIV=3 — verbatim from legacy. */
> +	reg = PWM_EN | FIELD_PREP(PWM_PER_PRE_MASK, 3) |
> +	      FIELD_PREP(PWM_PER_DIV_MASK, 3);
> +	ret = pm8901_tm_write_pwm(chip, reg);
> +	if (ret)
> +		goto out;
> +
> +	/* Prime the cached temperature from current hardware state. */
> +	chip->initialised = false;
> +	ret = pm8901_tm_update_temp_locked(chip);
> +
> +out:
> +	mutex_unlock(&chip->lock);
> +	return ret;
> +}
> +
> +static int pm8901_tm_probe(struct platform_device *pdev)
> +{
> +	struct pm8901_tm_chip *chip;
> +	int ret, irq_alarm, irq_hi_alarm;
> +	u32 res;
> +
> +	chip = devm_kzalloc(&pdev->dev, sizeof(*chip), GFP_KERNEL);
> +	if (!chip)
> +		return -ENOMEM;
> +
> +	chip->dev = &pdev->dev;
> +	mutex_init(&chip->lock);
> +
> +	chip->map = dev_get_regmap(pdev->dev.parent, NULL);
> +	if (!chip->map)
> +		return dev_err_probe(&pdev->dev, -ENXIO,
> +				     "no regmap on PM8901 parent\n");
> +
> +	ret = of_property_read_u32(pdev->dev.of_node, "reg", &res);
> +	if (ret)
> +		return dev_err_probe(&pdev->dev, ret,
> +				     "missing reg property\n");
> +	chip->base = res;
> +
> +	irq_alarm = platform_get_irq_byname(pdev, "alarm");
> +	if (irq_alarm < 0)
> +		return irq_alarm;
> +	irq_hi_alarm = platform_get_irq_byname(pdev, "hi-alarm");
> +	if (irq_hi_alarm < 0)
> +		return irq_hi_alarm;
> +
> +	ret = pm8901_tm_init_hw(chip);
> +	if (ret)
> +		return dev_err_probe(&pdev->dev, ret, "hw init failed\n");
> +
> +	chip->tz_dev = devm_thermal_of_zone_register(&pdev->dev, 0, chip,
> +						     &pm8901_tm_zone_ops);
> +	if (IS_ERR(chip->tz_dev))
> +		return dev_err_probe(&pdev->dev, PTR_ERR(chip->tz_dev),
> +				     "thermal zone register failed\n");
> +
> +	ret = devm_request_threaded_irq(&pdev->dev, irq_alarm, NULL,
> +					pm8901_tm_isr, IRQF_ONESHOT,
> +					"pm8901-tm-alarm", chip);
> +	if (ret)
> +		return dev_err_probe(&pdev->dev, ret,
> +				     "alarm IRQ request failed\n");
> +
> +	ret = devm_request_threaded_irq(&pdev->dev, irq_hi_alarm, NULL,
> +					pm8901_tm_isr, IRQF_ONESHOT,
> +					"pm8901-tm-hi-alarm", chip);
> +	if (ret)
> +		return dev_err_probe(&pdev->dev, ret,
> +				     "hi-alarm IRQ request failed\n");
> +
> +	platform_set_drvdata(pdev, chip);
> +	thermal_zone_device_update(chip->tz_dev, THERMAL_EVENT_UNSPECIFIED);
> +
> +	dev_info(&pdev->dev,

dev_dbg() or drop it completely.

> +		 "PM8901 thermal alarm: base=0x%x stage=%u thresh=%u temp=%d\n",
> +		 chip->base, chip->stage, chip->thresh, chip->temp);
> +
> +	return 0;
> +}
> +
> +static void pm8901_tm_remove(struct platform_device *pdev)
> +{
> +	struct pm8901_tm_chip *chip = platform_get_drvdata(pdev);
> +	u8 reg;
> +
> +	/*
> +	 * Disable software override on the way out so the PMIC reverts to
> +	 * its hardware auto-cut behaviour if the kernel is no longer the
> +	 * shutdown agent. Best-effort: ignore errors.
> +	 */
> +	mutex_lock(&chip->lock);
> +	if (!pm8901_tm_read_ctrl(chip, &reg)) {
> +		reg &= ~CTRL_OVRD_MASK;
> +		pm8901_tm_write_ctrl(chip, reg);
> +	}
> +	mutex_unlock(&chip->lock);
> +}
> +
> +static const struct of_device_id pm8901_tm_match_table[] = {
> +	{ .compatible = "qcom,pm8901-temp-alarm" },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(of, pm8901_tm_match_table);
> +
> +static struct platform_driver pm8901_tm_driver = {
> +	.driver = {
> +		.name		= "pm8901-temp-alarm",
> +		.of_match_table	= pm8901_tm_match_table,
> +	},
> +	.probe	= pm8901_tm_probe,
> +	.remove	= pm8901_tm_remove,
> +};
> +module_platform_driver(pm8901_tm_driver);
> +
> +MODULE_ALIAS("platform:pm8901-temp-alarm");

No need for platform aliases (neither here nor in any other driver which
has MODULE_DEVICE_TABLE(of).

> +MODULE_DESCRIPTION("Qualcomm PM8901 PMIC Thermal Alarm driver");
> +MODULE_LICENSE("GPL v2");
> -- 
> 2.43.0
> 

-- 
With best wishes
Dmitry