drivers/hwmon/nct6775-i2c.c

Source file repositories/reference/linux-study-clean/drivers/hwmon/nct6775-i2c.c

File Facts

System
Linux kernel
Corpus path
drivers/hwmon/nct6775-i2c.c
Extension
.c
Size
6234 bytes
Lines
188
Domain
Driver Families
Bucket
drivers/hwmon
Inferred role
Driver Families: implementation source
Status
source implementation candidate

Why This File Exists

Repeatable hardware-adapter layer. Deep compatibility for every driver is out of scope; this atlas records patterns, probe lifecycles, bus glue, IRQ/DMA usage, and links back to core abstractions.

Dependency Surface

Detected Declarations

Annotated Snippet

// 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.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, },
	{ .compatible = "nuvoton,nct6799", .data = (void *)nct6799, },

Annotation

Implementation Notes