[PATCH v4 7/7] hwmon: (nct6775) Add i2c driver

Zev Weiss
2022-04-27T01:02:45Z

This driver provides an i2c I/O mechanism for the core nct6775 driver,
as might be used by a BMC. Because the Super I/O chip is shared with
the host CPU in such a scenario (and the host should ultimately be in
control of it), the i2c driver is strictly read-only to avoid
interfering with any usage by the host (aside from the bank-select
register, which seems to be replicated for the i2c interface).

Signed-off-by: Zev Weiss <zev@bewilderbeest.net>
Tested-by: Renze Nicolai <renze@rnplus.nl>
---
MAINTAINERS | 6 ++
drivers/hwmon/Kconfig | 17 ++++
drivers/hwmon/Makefile | 1 +
drivers/hwmon/nct6775-i2c.c | 195 ++++++++++++++++++++++++++++++++++++
4 files changed, 219 insertions(+)
create mode 100644 drivers/hwmon/nct6775-i2c.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 88fdb7cb3197..01b97298f154 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -13538,6 +13538,12 @@ F: drivers/hwmon/nct6775-core.c
F: drivers/hwmon/nct6775-platform.c
F: drivers/hwmon/nct6775.h

+NCT6775 HARDWARE MONITOR DRIVER - I2C DRIVER
+M: Zev Weiss <zev@bewilderbeest.net>
+L: linux-hwmon@vger.kernel.org
+S: Maintained
+F: drivers/hwmon/nct6775-i2c.c
+
NETDEVSIM
M: Jakub Kicinski <kuba@kernel.org>
S: Maintained
diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
index 85c22bba439b..a1dac1aa4e3a 100644
--- a/drivers/hwmon/Kconfig
+++ b/drivers/hwmon/Kconfig
@@ -1489,6 +1489,23 @@ config SENSORS_NCT6775
This driver can also be built as a module. If so, the module
will be called nct6775.

+config SENSORS_NCT6775_I2C
+ tristate "I2C driver for Nuvoton NCT6775F and compatibles"
+ depends on I2C
+ select REGMAP_I2C
+ select SENSORS_NCT6775
+ help
+ If you say yes here you get support for the hardware monitoring
+ functionality of the Nuvoton NCT6106D, NCT6775F, NCT6776F, NCT6779D,
+ NCT6791D, NCT6792D, NCT6793D, NCT6795D, NCT6796D, and compatible
+ Super-I/O chips via their I2C interface.
+
+ If you're not building a kernel for a BMC, this is probably
+ not the driver you want (see CONFIG_SENSORS_NCT6775_PLATFORM).
+
+ This driver can also be built as a module. If so, the module
+ will be called nct6775-i2c.
+
config SENSORS_NCT7802
tristate "Nuvoton NCT7802Y"
depends on I2C
diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
index 93f2b774cc5e..004ab87c9b80 100644
--- a/drivers/hwmon/Makefile
+++ b/drivers/hwmon/Makefile
@@ -157,6 +157,7 @@ obj-$(CONFIG_SENSORS_NCT6683) += nct6683.o
obj-$(CONFIG_SENSORS_NCT6775_CORE) += nct6775-core.o
nct6775-objs := nct6775-platform.o
obj-$(CONFIG_SENSORS_NCT6775) += nct6775.o
+obj-$(CONFIG_SENSORS_NCT6775_I2C) += nct6775-i2c.o
obj-$(CONFIG_SENSORS_NCT7802) += nct7802.o
obj-$(CONFIG_SENSORS_NCT7904) += nct7904.o
obj-$(CONFIG_SENSORS_NPCM7XX) += npcm750-pwm-fan.o
diff --git a/drivers/hwmon/nct6775-i2c.c b/drivers/hwmon/nct6775-i2c.c
new file mode 100644
index 000000000000..e1bcd1146191
--- /dev/null
+++ b/drivers/hwmon/nct6775-i2c.c
@@ -0,0 +1,195 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * nct6775-i2c - I2C driver for the hardware monitoring functionality of
+ * Nuvoton NCT677x Super-I/O chips
+ *
+ * Copyright (C) 2022 Zev Weiss <zev@bewilderbeest.net>
+ *
+ * This driver interacts with the chip via it's "back door" i2c interface, as
+ * is often exposed to a BMC. Because the host may still be operating the
+ * chip via the ("front door") LPC interface, this driver cannot assume that
+ * it actually has full control of the chip, and in particular must avoid
+ * making any changes that could confuse the host's LPC usage of it. It thus
+ * operates in a strictly read-only fashion, with the only exception being the
+ * bank-select register (which seems, thankfully, to be replicated for the i2c
+ * interface so it doesn't affect the LPC interface).
+ */
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/i2c.h>
+#include <linux/hwmon.h>
+#include <linux/hwmon-sysfs.h>
+#include <linux/err.h>
+#include <linux/of_device.h>
+#include <linux/regmap.h>
+#include "nct6775.h"
+
+static int nct6775_i2c_read(void *ctx, unsigned int reg, unsigned int *val)
+{
+ int ret;
+ u32 tmp;
+ u8 bank = reg >> 8;
+ struct nct6775_data *data = ctx;
+ struct i2c_client *client = data->driver_data;
+
+ if (bank != data->bank) {
+ ret = i2c_smbus_write_byte_data(client, NCT6775_REG_BANK, bank);
+ if (ret)
+ return ret;
+ data->bank = bank;
+ }
+
+ ret = i2c_smbus_read_byte_data(client, reg & 0xff);
+ if (ret < 0)
+ return ret;
+ tmp = ret;
+
+ if (nct6775_reg_is_word_sized(data, reg)) {
+ ret = i2c_smbus_read_byte_data(client, (reg & 0xff) + 1);
+ if (ret < 0)
+ return ret;
+ tmp = (tmp << 8) | ret;
+ }
+
+ *val = tmp;
+ return 0;
+}
+
+/*
+ * The write operation is a dummy so as not to disturb anything being done
+ * with the chip via LPC.
+ */
+static int nct6775_i2c_write(void *ctx, unsigned int reg, unsigned int value)
+{
+ struct nct6775_data *data = ctx;
+ struct i2c_client *client = data->driver_data;
+
+ dev_dbg(&client->dev, "skipping attempted write: %02x -> %03x\n", value, reg);
+
+ /*
+ * This is a lie, but writing anything but the bank-select register is
+ * something this driver shouldn't be doing.
+ */
+ return 0;
+}
+
+static const struct of_device_id __maybe_unused nct6775_i2c_of_match[] = {
+ { .compatible = "nuvoton,nct6106", .data = (void *)nct6106, },
+ { .compatible = "nuvoton,nct6116", .data = (void *)nct6116, },
+ { .compatible = "nuvoton,nct6775", .data = (void *)nct6775, },
+ { .compatible = "nuvoton,nct6776", .data = (void *)nct6776, },
+ { .compatible = "nuvoton,nct6779", .data = (void *)nct6779, },
+ { .compatible = "nuvoton,nct6791", .data = (void *)nct6791, },
+ { .compatible = "nuvoton,nct6792", .data = (void *)nct6792, },
+ { .compatible = "nuvoton,nct6793", .data = (void *)nct6793, },
+ { .compatible = "nuvoton,nct6795", .data = (void *)nct6795, },
+ { .compatible = "nuvoton,nct6796", .data = (void *)nct6796, },
+ { .compatible = "nuvoton,nct6797", .data = (void *)nct6797, },
+ { .compatible = "nuvoton,nct6798", .data = (void *)nct6798, },
+ { },
+};
+MODULE_DEVICE_TABLE(of, nct6775_i2c_of_match);
+
+static const struct i2c_device_id nct6775_i2c_id[] = {
+ { "nct6106", nct6106 },
+ { "nct6116", nct6116 },
+ { "nct6775", nct6775 },
+ { "nct6776", nct6776 },
+ { "nct6779", nct6779 },
+ { "nct6791", nct6791 },
+ { "nct6792", nct6792 },
+ { "nct6793", nct6793 },
+ { "nct6795", nct6795 },
+ { "nct6796", nct6796 },
+ { "nct6797", nct6797 },
+ { "nct6798", nct6798 },
+ { }
+};
+MODULE_DEVICE_TABLE(i2c, nct6775_i2c_id);
+
+static int nct6775_i2c_probe_init(struct nct6775_data *data)
+{
+ u32 tsi_channel_mask;
+ struct i2c_client *client = data->driver_data;
+
+ /*
+ * The i2c interface doesn't provide access to the control registers
+ * needed to determine the presence of other fans, but fans 1 and 2
+ * are (in principle) always there.
+ *
+ * In practice this is perhaps a little silly, because the system
+ * using this driver is mostly likely a BMC, and hence probably has
+ * totally separate fan tachs & pwms of its own that are actually
+ * controlling/monitoring the fans -- these are thus unlikely to be
+ * doing anything actually useful.
+ */
+ data->has_fan = 0x03;
+ data->has_fan_min = 0x03;
+ data->has_pwm = 0x03;
+
+ /*
+ * Because on a BMC this driver may be bound very shortly after power
+ * is first applied to the device, the automatic TSI channel detection
+ * in nct6775_probe() (which has already been run at this point) may
+ * not find anything if a channel hasn't yet produced a temperature
+ * reading. Augment whatever was found via autodetection (if
+ * anything) with the channels DT says should be active.
+ */
+ if (!of_property_read_u32(client->dev.of_node, "nuvoton,tsi-channel-mask",
+ &tsi_channel_mask))
+ data->have_tsi_temp |= tsi_channel_mask & GENMASK(NUM_TSI_TEMP - 1, 0);
+
+ return 0;
+}
+
+static const struct regmap_config nct6775_i2c_regmap_config = {
+ .reg_bits = 16,
+ .val_bits = 16,
+ .reg_read = nct6775_i2c_read,
+ .reg_write = nct6775_i2c_write,
+};
+
+static int nct6775_i2c_probe(struct i2c_client *client)
+{
+ struct nct6775_data *data;
+ const struct of_device_id *of_id;
+ const struct i2c_device_id *i2c_id;
+ struct device *dev = &client->dev;
+
+ of_id = of_match_device(nct6775_i2c_of_match, dev);
+ i2c_id = i2c_match_id(nct6775_i2c_id, client);
+
+ if (of_id && (unsigned long)of_id->data != i2c_id->driver_data)
+ dev_notice(dev, "Device mismatch: %s in device tree, %s detected\n",
+ of_id->name, i2c_id->name);
+
+ data = devm_kzalloc(&client->dev, sizeof(*data), GFP_KERNEL);
+ if (!data)
+ return -ENOMEM;
+
+ data->kind = i2c_id->driver_data;
+
+ data->read_only = true;
+ data->driver_data = client;
+ data->driver_init = nct6775_i2c_probe_init;
+
+ return nct6775_probe(dev, data, &nct6775_i2c_regmap_config);
+}
+
+static struct i2c_driver nct6775_i2c_driver = {
+ .class = I2C_CLASS_HWMON,
+ .driver = {
+ .name = "nct6775-i2c",
+ .of_match_table = of_match_ptr(nct6775_i2c_of_match),
+ },
+ .probe_new = nct6775_i2c_probe,
+ .id_table = nct6775_i2c_id,
+};
+
+module_i2c_driver(nct6775_i2c_driver);
+
+MODULE_AUTHOR("Zev Weiss <zev@bewilderbeest.net>");
+MODULE_DESCRIPTION("I2C driver for NCT6775F and compatible chips");
+MODULE_LICENSE("GPL");
+MODULE_IMPORT_NS(HWMON_NCT6775);
--
2.36.0