1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * nct6775-i2c - I2C driver for the hardware monitoring functionality of
  4 *	         Nuvoton NCT677x Super-I/O chips
  5 *
  6 * Copyright (C) 2022 Zev Weiss <zev@bewilderbeest.net>
  7 *
  8 * This driver interacts with the chip via it's "back door" i2c interface, as
  9 * is often exposed to a BMC.  Because the host may still be operating the
 10 * chip via the ("front door") LPC interface, this driver cannot assume that
 11 * it actually has full control of the chip, and in particular must avoid
 12 * making any changes that could confuse the host's LPC usage of it.  It thus
 13 * operates in a strictly read-only fashion, with the only exception being the
 14 * bank-select register (which seems, thankfully, to be replicated for the i2c
 15 * interface so it doesn't affect the LPC interface).
 16 */
 17
 18#include <linux/module.h>
 19#include <linux/init.h>
 20#include <linux/i2c.h>
 21#include <linux/hwmon.h>
 22#include <linux/hwmon-sysfs.h>
 23#include <linux/err.h>
 24#include <linux/of.h>
 25#include <linux/regmap.h>
 26#include "nct6775.h"
 27
 28static int nct6775_i2c_read(void *ctx, unsigned int reg, unsigned int *val)
 29{
 30	int ret;
 31	u32 tmp;
 32	u8 bank = reg >> 8;
 33	struct nct6775_data *data = ctx;
 34	struct i2c_client *client = data->driver_data;
 35
 36	if (bank != data->bank) {
 37		ret = i2c_smbus_write_byte_data(client, NCT6775_REG_BANK, bank);
 38		if (ret)
 39			return ret;
 40		data->bank = bank;
 41	}
 42
 43	ret = i2c_smbus_read_byte_data(client, reg & 0xff);
 44	if (ret < 0)
 45		return ret;
 46	tmp = ret;
 47
 48	if (nct6775_reg_is_word_sized(data, reg)) {
 49		ret = i2c_smbus_read_byte_data(client, (reg & 0xff) + 1);
 50		if (ret < 0)
 51			return ret;
 52		tmp = (tmp << 8) | ret;
 53	}
 54
 55	*val = tmp;
 56	return 0;
 57}
 58
 59/*
 60 * The write operation is a dummy so as not to disturb anything being done
 61 * with the chip via LPC.
 62 */
 63static int nct6775_i2c_write(void *ctx, unsigned int reg, unsigned int value)
 64{
 65	struct nct6775_data *data = ctx;
 66	struct i2c_client *client = data->driver_data;
 67
 68	dev_dbg(&client->dev, "skipping attempted write: %02x -> %03x\n", value, reg);
 69
 70	/*
 71	 * This is a lie, but writing anything but the bank-select register is
 72	 * something this driver shouldn't be doing.
 73	 */
 74	return 0;
 75}
 76
 77static const struct of_device_id __maybe_unused nct6775_i2c_of_match[] = {
 78	{ .compatible = "nuvoton,nct6106", .data = (void *)nct6106, },
 79	{ .compatible = "nuvoton,nct6116", .data = (void *)nct6116, },
 80	{ .compatible = "nuvoton,nct6775", .data = (void *)nct6775, },
 81	{ .compatible = "nuvoton,nct6776", .data = (void *)nct6776, },
 82	{ .compatible = "nuvoton,nct6779", .data = (void *)nct6779, },
 83	{ .compatible = "nuvoton,nct6791", .data = (void *)nct6791, },
 84	{ .compatible = "nuvoton,nct6792", .data = (void *)nct6792, },
 85	{ .compatible = "nuvoton,nct6793", .data = (void *)nct6793, },
 86	{ .compatible = "nuvoton,nct6795", .data = (void *)nct6795, },
 87	{ .compatible = "nuvoton,nct6796", .data = (void *)nct6796, },
 88	{ .compatible = "nuvoton,nct6797", .data = (void *)nct6797, },
 89	{ .compatible = "nuvoton,nct6798", .data = (void *)nct6798, },
 90	{ .compatible = "nuvoton,nct6799", .data = (void *)nct6799, },
 91	{ },
 92};
 93MODULE_DEVICE_TABLE(of, nct6775_i2c_of_match);
 94
 95static const struct i2c_device_id nct6775_i2c_id[] = {
 96	{ "nct6106", nct6106 },
 97	{ "nct6116", nct6116 },
 98	{ "nct6775", nct6775 },
 99	{ "nct6776", nct6776 },
100	{ "nct6779", nct6779 },
101	{ "nct6791", nct6791 },
102	{ "nct6792", nct6792 },
103	{ "nct6793", nct6793 },
104	{ "nct6795", nct6795 },
105	{ "nct6796", nct6796 },
106	{ "nct6797", nct6797 },
107	{ "nct6798", nct6798 },
108	{ "nct6799", nct6799 },
109	{ }
110};
111MODULE_DEVICE_TABLE(i2c, nct6775_i2c_id);
112
113static int nct6775_i2c_probe_init(struct nct6775_data *data)
114{
115	u32 tsi_channel_mask;
116	struct i2c_client *client = data->driver_data;
117
118	/*
119	 * The i2c interface doesn't provide access to the control registers
120	 * needed to determine the presence of other fans, but fans 1 and 2
121	 * are (in principle) always there.
122	 *
123	 * In practice this is perhaps a little silly, because the system
124	 * using this driver is mostly likely a BMC, and hence probably has
125	 * totally separate fan tachs & pwms of its own that are actually
126	 * controlling/monitoring the fans -- these are thus unlikely to be
127	 * doing anything actually useful.
128	 */
129	data->has_fan = 0x03;
130	data->has_fan_min = 0x03;
131	data->has_pwm = 0x03;
132
133	/*
134	 * Because on a BMC this driver may be bound very shortly after power
135	 * is first applied to the device, the automatic TSI channel detection
136	 * in nct6775_probe() (which has already been run at this point) may
137	 * not find anything if a channel hasn't yet produced a temperature
138	 * reading.  Augment whatever was found via autodetection (if
139	 * anything) with the channels DT says should be active.
140	 */
141	if (!of_property_read_u32(client->dev.of_node, "nuvoton,tsi-channel-mask",
142				  &tsi_channel_mask))
143		data->have_tsi_temp |= tsi_channel_mask & GENMASK(NUM_TSI_TEMP - 1, 0);
144
145	return 0;
146}
147
148static const struct regmap_config nct6775_i2c_regmap_config = {
149	.reg_bits = 16,
150	.val_bits = 16,
151	.reg_read = nct6775_i2c_read,
152	.reg_write = nct6775_i2c_write,
153};
154
155static int nct6775_i2c_probe(struct i2c_client *client)
156{
157	struct nct6775_data *data;
158	struct device *dev = &client->dev;
159
160	data = devm_kzalloc(&client->dev, sizeof(*data), GFP_KERNEL);
161	if (!data)
162		return -ENOMEM;
163
164	data->kind = (enum kinds)(uintptr_t)i2c_get_match_data(client);
165	data->read_only = true;
166	data->driver_data = client;
167	data->driver_init = nct6775_i2c_probe_init;
168
169	return nct6775_probe(dev, data, &nct6775_i2c_regmap_config);
170}
171
172static struct i2c_driver nct6775_i2c_driver = {
173	.class = I2C_CLASS_HWMON,
174	.driver = {
175		.name = "nct6775-i2c",
176		.of_match_table = of_match_ptr(nct6775_i2c_of_match),
177	},
178	.probe = nct6775_i2c_probe,
179	.id_table = nct6775_i2c_id,
180};
181
182module_i2c_driver(nct6775_i2c_driver);
183
184MODULE_AUTHOR("Zev Weiss <zev@bewilderbeest.net>");
185MODULE_DESCRIPTION("I2C driver for NCT6775F and compatible chips");
186MODULE_LICENSE("GPL");
187MODULE_IMPORT_NS(HWMON_NCT6775);