hwmon: sy7636a: Add temperature driver for sy7636a

This is a multi-function device to interface with the sy7636a
EPD PMIC chip from Silergy.

Signed-off-by: Alistair Francis <alistair@alistair23.me>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

Documentation/hwmon/index.rst

@@ -185,6 +185,7 @@ Hardware Monitoring Kernel Drivers
    smsc47m1
    sparx5-temp
    stpddc60
+   sy7636a-hwmon
    tc654
    tc74
    thmc50

Documentation/hwmon/sy7636a-hwmon.rst

@@ -0,0 +1,26 @@
+.. SPDX-License-Identifier: GPL-2.0-or-later
+
+Kernel driver sy7636a-hwmon
+=========================
+
+Supported chips:
+
+ * Silergy SY7636A PMIC
+
+
+Description
+-----------
+
+This driver adds hardware temperature reading support for
+the Silergy SY7636A PMIC.
+
+The following sensors are supported
+
+  * Temperature
+      - SoC on-die temperature in milli-degree C
+
+sysfs-Interface
+---------------
+
+temp0_input
+	- SoC on-die temperature (milli-degree C)

drivers/hwmon/Kconfig

@@ -1672,6 +1672,15 @@ config SENSORS_SIS5595
 	  This driver can also be built as a module. If so, the module
 	  will be called sis5595.
 
+config SENSORS_SY7636A
+	tristate "Silergy SY7636A"
+	help
+	  If you say yes here you get support for the thermistor readout of
+	  the Silergy SY7636A PMIC.
+
+	  This driver can also be built as a module.  If so, the module
+	  will be called sy7636a-hwmon.
+
 config SENSORS_DME1737
 	tristate "SMSC DME1737, SCH311x and compatibles"
 	depends on I2C && !PPC

drivers/hwmon/Makefile

@@ -186,6 +186,7 @@ obj-$(CONFIG_SENSORS_SMSC47M1)	+= smsc47m1.o
 obj-$(CONFIG_SENSORS_SMSC47M192)+= smsc47m192.o
 obj-$(CONFIG_SENSORS_SPARX5)	+= sparx5-temp.o
 obj-$(CONFIG_SENSORS_STTS751)	+= stts751.o
+obj-$(CONFIG_SENSORS_SY7636A)	+= sy7636a-hwmon.o
 obj-$(CONFIG_SENSORS_AMC6821)	+= amc6821.o
 obj-$(CONFIG_SENSORS_TC74)	+= tc74.o
 obj-$(CONFIG_SENSORS_THMC50)	+= thmc50.o

drivers/hwmon/sy7636a-hwmon.c

@@ -0,0 +1,106 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Functions to access SY3686A power management chip temperature
+ *
+ * Copyright (C) 2021 reMarkable AS - http://www.remarkable.com/
+ *
+ * Authors: Lars Ivar Miljeteig <lars.ivar.miljeteig@remarkable.com>
+ *          Alistair Francis <alistair@alistair23.me>
+ */
+
+#include <linux/err.h>
+#include <linux/hwmon.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+#include <linux/regulator/machine.h>
+
+#include <linux/mfd/sy7636a.h>
+
+static int sy7636a_read(struct device *dev, enum hwmon_sensor_types type,
+			u32 attr, int channel, long *temp)
+{
+	struct regmap *regmap = dev_get_drvdata(dev);
+	int ret, reg_val;
+
+	ret = regmap_read(regmap,
+			  SY7636A_REG_TERMISTOR_READOUT, &reg_val);
+	if (ret)
+		return ret;
+
+	*temp = reg_val * 1000;
+
+	return 0;
+}
+
+static umode_t sy7636a_is_visible(const void *data,
+				  enum hwmon_sensor_types type,
+				  u32 attr, int channel)
+{
+	if (type != hwmon_temp)
+		return 0;
+
+	if (attr != hwmon_temp_input)
+		return 0;
+
+	return 0444;
+}
+
+static const struct hwmon_ops sy7636a_hwmon_ops = {
+	.is_visible = sy7636a_is_visible,
+	.read = sy7636a_read,
+};
+
+static const struct hwmon_channel_info *sy7636a_info[] = {
+	HWMON_CHANNEL_INFO(chip, HWMON_C_REGISTER_TZ),
+	HWMON_CHANNEL_INFO(temp, HWMON_T_INPUT),
+	NULL
+};
+
+static const struct hwmon_chip_info sy7636a_chip_info = {
+	.ops = &sy7636a_hwmon_ops,
+	.info = sy7636a_info,
+};
+
+static int sy7636a_sensor_probe(struct platform_device *pdev)
+{
+	struct regmap *regmap = dev_get_regmap(pdev->dev.parent, NULL);
+	struct regulator *regulator;
+	struct device *hwmon_dev;
+	int err;
+
+	if (!regmap)
+		return -EPROBE_DEFER;
+
+	regulator = devm_regulator_get(&pdev->dev, "vcom");
+	if (IS_ERR(regulator))
+		return PTR_ERR(regulator);
+
+	err = regulator_enable(regulator);
+	if (err)
+		return err;
+
+	hwmon_dev = devm_hwmon_device_register_with_info(&pdev->dev,
+							 "sy7636a_temperature", regmap,
+							 &sy7636a_chip_info, NULL);
+
+	if (IS_ERR(hwmon_dev)) {
+		err = PTR_ERR(hwmon_dev);
+		dev_err(&pdev->dev, "Unable to register hwmon device, returned %d\n", err);
+		return err;
+	}
+
+	return 0;
+}
+
+static struct platform_driver sy7636a_sensor_driver = {
+	.probe = sy7636a_sensor_probe,
+	.driver = {
+		.name = "sy7636a-temperature",
+	},
+};
+module_platform_driver(sy7636a_sensor_driver);
+
+MODULE_DESCRIPTION("SY7636A sensor driver");
+MODULE_LICENSE("GPL");