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