1 // SPDX-License-Identifier: GPL-2.0+
2 /*
3  * Raspberry Pi voltage sensor driver
4  *
5  * Based on firmware/raspberrypi.c by Noralf Trønnes
6  *
7  * Copyright (C) 2018 Stefan Wahren <stefan.wahren@i2se.com>
8  */
9 #include <linux/device.h>
10 #include <linux/err.h>
11 #include <linux/hwmon.h>
12 #include <linux/module.h>
13 #include <linux/platform_device.h>
14 #include <linux/slab.h>
15 #include <linux/workqueue.h>
16 #include <soc/bcm2835/raspberrypi-firmware.h>
17 
18 #define UNDERVOLTAGE_STICKY_BIT	BIT(16)
19 
20 struct rpi_hwmon_data {
21 	struct device *hwmon_dev;
22 	struct rpi_firmware *fw;
23 	u32 last_throttled;
24 	struct delayed_work get_values_poll_work;
25 };
26 
27 static void rpi_firmware_get_throttled(struct rpi_hwmon_data *data)
28 {
29 	u32 new_uv, old_uv, value;
30 	int ret;
31 
32 	/* Request firmware to clear sticky bits */
33 	value = 0xffff;
34 
35 	ret = rpi_firmware_property(data->fw, RPI_FIRMWARE_GET_THROTTLED,
36 				    &value, sizeof(value));
37 	if (ret) {
38 		dev_err_once(data->hwmon_dev, "Failed to get throttled (%d)\n",
39 			     ret);
40 		return;
41 	}
42 
43 	new_uv = value & UNDERVOLTAGE_STICKY_BIT;
44 	old_uv = data->last_throttled & UNDERVOLTAGE_STICKY_BIT;
45 	data->last_throttled = value;
46 
47 	if (new_uv == old_uv)
48 		return;
49 
50 	if (new_uv)
51 		dev_crit(data->hwmon_dev, "Undervoltage detected!\n");
52 	else
53 		dev_info(data->hwmon_dev, "Voltage normalised\n");
54 
55 	sysfs_notify(&data->hwmon_dev->kobj, NULL, "in0_lcrit_alarm");
56 }
57 
58 static void get_values_poll(struct work_struct *work)
59 {
60 	struct rpi_hwmon_data *data;
61 
62 	data = container_of(work, struct rpi_hwmon_data,
63 			    get_values_poll_work.work);
64 
65 	rpi_firmware_get_throttled(data);
66 
67 	/*
68 	 * We can't run faster than the sticky shift (100ms) since we get
69 	 * flipping in the sticky bits that are cleared.
70 	 */
71 	schedule_delayed_work(&data->get_values_poll_work, 2 * HZ);
72 }
73 
74 static int rpi_read(struct device *dev, enum hwmon_sensor_types type,
75 		    u32 attr, int channel, long *val)
76 {
77 	struct rpi_hwmon_data *data = dev_get_drvdata(dev);
78 
79 	*val = !!(data->last_throttled & UNDERVOLTAGE_STICKY_BIT);
80 	return 0;
81 }
82 
83 static umode_t rpi_is_visible(const void *_data, enum hwmon_sensor_types type,
84 			      u32 attr, int channel)
85 {
86 	return 0444;
87 }
88 
89 static const struct hwmon_channel_info *rpi_info[] = {
90 	HWMON_CHANNEL_INFO(in,
91 			   HWMON_I_LCRIT_ALARM),
92 	NULL
93 };
94 
95 static const struct hwmon_ops rpi_hwmon_ops = {
96 	.is_visible = rpi_is_visible,
97 	.read = rpi_read,
98 };
99 
100 static const struct hwmon_chip_info rpi_chip_info = {
101 	.ops = &rpi_hwmon_ops,
102 	.info = rpi_info,
103 };
104 
105 static int rpi_hwmon_probe(struct platform_device *pdev)
106 {
107 	struct device *dev = &pdev->dev;
108 	struct rpi_hwmon_data *data;
109 
110 	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
111 	if (!data)
112 		return -ENOMEM;
113 
114 	/* Parent driver assure that firmware is correct */
115 	data->fw = dev_get_drvdata(dev->parent);
116 
117 	data->hwmon_dev = devm_hwmon_device_register_with_info(dev, "rpi_volt",
118 							       data,
119 							       &rpi_chip_info,
120 							       NULL);
121 
122 	INIT_DELAYED_WORK(&data->get_values_poll_work, get_values_poll);
123 	platform_set_drvdata(pdev, data);
124 
125 	if (!PTR_ERR_OR_ZERO(data->hwmon_dev))
126 		schedule_delayed_work(&data->get_values_poll_work, 2 * HZ);
127 
128 	return PTR_ERR_OR_ZERO(data->hwmon_dev);
129 }
130 
131 static int rpi_hwmon_remove(struct platform_device *pdev)
132 {
133 	struct rpi_hwmon_data *data = platform_get_drvdata(pdev);
134 
135 	cancel_delayed_work_sync(&data->get_values_poll_work);
136 
137 	return 0;
138 }
139 
140 static struct platform_driver rpi_hwmon_driver = {
141 	.probe = rpi_hwmon_probe,
142 	.remove = rpi_hwmon_remove,
143 	.driver = {
144 		.name = "raspberrypi-hwmon",
145 	},
146 };
147 module_platform_driver(rpi_hwmon_driver);
148 
149 MODULE_AUTHOR("Stefan Wahren <stefan.wahren@i2se.com>");
150 MODULE_DESCRIPTION("Raspberry Pi voltage sensor driver");
151 MODULE_LICENSE("GPL v2");
152 MODULE_ALIAS("platform:raspberrypi-hwmon");
153