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Date:   Sun, 22 Nov 2020 23:54:49 -0800
From:   Tao Ren <rentao.bupt@gmail.com>
To:     Guenter Roeck <linux@roeck-us.net>
Cc:     Jean Delvare <jdelvare@suse.com>, Jonathan Corbet <corbet@lwn.net>,
        linux-hwmon@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, openbmc@lists.ozlabs.org,
        taoren@fb.com, mikechoi@fb.com
Subject: Re: [PATCH v3 1/2] hwmon: (max127) Add Maxim MAX127 hardware
 monitoring driver
Message-ID: <20201123075448.GA3563@taoren-ubuntu-R90MNF91>
References: <20201119175324.22472-1-rentao.bupt@gmail.com>
 <20201119175324.22472-2-rentao.bupt@gmail.com>
 <20201122183342.GA69512@roeck-us.net>
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On Sun, Nov 22, 2020 at 10:33:42AM -0800, Guenter Roeck wrote:
> On Thu, Nov 19, 2020 at 09:53:23AM -0800, rentao.bupt@gmail.com wrote:
> > From: Tao Ren <rentao.bupt@gmail.com>
> > 
> > Add hardware monitoring driver for the Maxim MAX127 chip.
> > 
> > MAX127 min/max range handling code is inspired by the max197 driver.
> > 
> > Signed-off-by: Tao Ren <rentao.bupt@gmail.com>
> 
> Nice cleanup. Couple of minor comments.
> 
> Thanks,
> Guenter
> 
> > ---
> >  Changes in v3:
> >    - no code change. xdp maintainers were removed from to/cc list.
> >  Changes in v2:
> >    - replace devm_hwmon_device_register_with_groups() with
> >      devm_hwmon_device_register_with_info() API.
> >    - divide min/max read and write methods to separate functions.
> >    - fix raw-to-vin conversion logic.
> >    - refine ctrl_byte handling so mutex is not needed to protect the
> >      byte.
> >    - improve i2c_transfer() error handling.
> >    - a few other improvements (comments, variable naming, and etc.).
> > 
> >  drivers/hwmon/Kconfig  |   9 ++
> >  drivers/hwmon/Makefile |   1 +
> >  drivers/hwmon/max127.c | 346 +++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 356 insertions(+)
> >  create mode 100644 drivers/hwmon/max127.c
> > 
> > diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
> > index 9d600e0c5584..716df51edc87 100644
> > --- a/drivers/hwmon/Kconfig
> > +++ b/drivers/hwmon/Kconfig
> > @@ -950,6 +950,15 @@ config SENSORS_MAX1111
> >  	  This driver can also be built as a module. If so, the module
> >  	  will be called max1111.
> >  
> > +config SENSORS_MAX127
> > +	tristate "Maxim MAX127 12-bit 8-channel Data Acquisition System"
> > +	depends on I2C
> > +	help
> > +	  Say y here to support Maxim's MAX127 DAS chips.
> > +
> > +	  This driver can also be built as a module. If so, the module
> > +	  will be called max127.
> > +
> >  config SENSORS_MAX16065
> >  	tristate "Maxim MAX16065 System Manager and compatibles"
> >  	depends on I2C
> > diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
> > index 1083bbfac779..01ca5d3fbad4 100644
> > --- a/drivers/hwmon/Makefile
> > +++ b/drivers/hwmon/Makefile
> > @@ -127,6 +127,7 @@ obj-$(CONFIG_SENSORS_LTC4260)	+= ltc4260.o
> >  obj-$(CONFIG_SENSORS_LTC4261)	+= ltc4261.o
> >  obj-$(CONFIG_SENSORS_LTQ_CPUTEMP) += ltq-cputemp.o
> >  obj-$(CONFIG_SENSORS_MAX1111)	+= max1111.o
> > +obj-$(CONFIG_SENSORS_MAX127)	+= max127.o
> >  obj-$(CONFIG_SENSORS_MAX16065)	+= max16065.o
> >  obj-$(CONFIG_SENSORS_MAX1619)	+= max1619.o
> >  obj-$(CONFIG_SENSORS_MAX1668)	+= max1668.o
> > diff --git a/drivers/hwmon/max127.c b/drivers/hwmon/max127.c
> > new file mode 100644
> > index 000000000000..3df4c225a6a2
> > --- /dev/null
> > +++ b/drivers/hwmon/max127.c
> > @@ -0,0 +1,346 @@
> > +// SPDX-License-Identifier: GPL-2.0+
> > +/*
> > + * Hardware monitoring driver for MAX127.
> > + *
> > + * Copyright (c) 2020 Facebook Inc.
> > + */
> > +
> > +#include <linux/err.h>
> > +#include <linux/hwmon.h>
> > +#include <linux/hwmon-sysfs.h>
> 
> Not needed.
> 
> > +#include <linux/i2c.h>
> > +#include <linux/init.h>
> > +#include <linux/module.h>
> > +#include <linux/sysfs.h>
> 
> Not needed.

Thanks for pointing it out. Both includes are deleted in v4.

> 
> > +
> > +/*
> > + * MAX127 Control Byte. Refer to MAX127 datasheet, Table 1 "Control-Byte
> > + * Format" for details.
> > + */
> > +#define MAX127_CTRL_START	BIT(7)
> > +#define MAX127_CTRL_SEL_SHIFT	4
> > +#define MAX127_CTRL_RNG		BIT(3)
> > +#define MAX127_CTRL_BIP		BIT(2)
> > +#define MAX127_CTRL_PD1		BIT(1)
> > +#define MAX127_CTRL_PD0		BIT(0)
> > +
> > +#define MAX127_NUM_CHANNELS	8
> > +#define MAX127_SET_CHANNEL(ch)	(((ch) & 7) << MAX127_CTRL_SEL_SHIFT)
> > +
> > +/*
> > + * MAX127 channel input ranges. Refer to MAX127 datasheet, Table 3 "Range
> > + * and Polarity Selection" for details.
> > + */
> > +#define MAX127_FULL_RANGE	10000	/* 10V */
> > +#define MAX127_HALF_RANGE	5000	/* 5V */
> > +
> > +/*
> > + * MAX127 returns 2 bytes at read:
> > + *   - the first byte contains data[11:4].
> > + *   - the second byte contains data[3:0] (MSB) and 4 dummy 0s (LSB).
> > + * Refer to MAX127 datasheet, "Read a Conversion (Read Cycle)" section
> > + * for details.
> > + */
> > +#define MAX127_DATA_LEN		2
> > +#define MAX127_DATA_SHIFT	4
> > +
> > +#define MAX127_SIGN_BIT		BIT(11)
> > +
> > +struct max127_data {
> > +	struct mutex lock;
> > +	struct i2c_client *client;
> > +	u8 ctrl_byte[MAX127_NUM_CHANNELS];
> > +};
> > +
> > +static int max127_select_channel(struct i2c_client *client, u8 ctrl_byte)
> > +{
> > +	int status;
> > +	struct i2c_msg msg = {
> > +		.addr = client->addr,
> > +		.flags = 0,
> > +		.len = sizeof(ctrl_byte),
> > +		.buf = &ctrl_byte,
> > +	};
> > +
> > +	status = i2c_transfer(client->adapter, &msg, 1);
> > +	if (status < 0)
> > +		return status;
> > +	else if (status != 1)
> 
> else after return is not needed.
> 
> > +		return -EIO;
> > +
> > +	return 0;
> > +}
> > +
> > +static int max127_read_channel(struct i2c_client *client, long *val)
> > +{
> > +	int status;
> > +	u8 i2c_data[MAX127_DATA_LEN];
> > +	struct i2c_msg msg = {
> > +		.addr = client->addr,
> > +		.flags = I2C_M_RD,
> > +		.len = sizeof(i2c_data),
> > +		.buf = i2c_data,
> > +	};
> > +
> > +	status = i2c_transfer(client->adapter, &msg, 1);
> > +	if (status < 0)
> > +		return status;
> > +	else if (status != 1)
> 
> else after return is not needed.

I'm not sure if I understand your suggestion correctly, and I added this
branch to handle the case when i2c_transfer() returns 0, which means the
message is not transferred. Perhaps it would never happen? but anyhow, I
just simplified the check in v4; please kindly review and let me know if
you have further suggestions.

> 
> > +		return -EIO;
> > +
> > +	*val = (i2c_data[1] >> MAX127_DATA_SHIFT) |
> > +		((u16)i2c_data[0] << MAX127_DATA_SHIFT);
> > +	return 0;
> > +}
> > +
> > +static long max127_process_raw(u8 ctrl_byte, long raw)
> > +{
> > +	long scale, weight;
> > +
> > +	/*
> > +	 * MAX127's data coding is binary in unipolar mode with 1 LSB =
> > +	 * (Full-Scale/4096) and two’s complement binary in bipolar mode
> > +	 * with 1 LSB = [(2 x |FS|)/4096].
> > +	 * Refer to MAX127 datasheet, "Transfer Function" section for
> > +	 * details.
> > +	 */
> > +	scale = (ctrl_byte & MAX127_CTRL_RNG) ? MAX127_FULL_RANGE :
> > +						MAX127_HALF_RANGE;
> > +	if (ctrl_byte & MAX127_CTRL_BIP) {
> > +		weight = (raw & MAX127_SIGN_BIT);
> > +		raw &= ~MAX127_SIGN_BIT;
> > +		raw -= weight;
> > +		raw *= 2;
> > +	}
> > +
> > +	return raw * scale / 4096;
> > +}
> > +
> > +static int max127_read_input(struct max127_data *data, int channel, long *val)
> > +{
> > +	long raw;
> > +	int status;
> > +	struct i2c_client *client = data->client;
> > +	u8 ctrl_byte = data->ctrl_byte[channel];
> > +
> > +	mutex_lock(&data->lock);
> > +
> > +	status = max127_select_channel(client, ctrl_byte);
> > +	if (status)
> > +		goto exit;
> > +
> > +	status = max127_read_channel(client, &raw);
> > +	if (status)
> > +		goto exit;
> > +
> > +	*val = max127_process_raw(ctrl_byte, raw);
> > +
> > +exit:
> > +	mutex_unlock(&data->lock);
> > +	return status;
> > +}
> > +
> > +static int max127_read_min(struct max127_data *data, int channel, long *val)
> > +{
> > +	u8 rng_bip = (data->ctrl_byte[channel] >> 2) & 3;
> > +	static const int min_input_map[4] = {
> > +		0,			/* RNG=0, BIP=0 */
> > +		-MAX127_HALF_RANGE,	/* RNG=0, BIP=1 */
> > +		0,			/* RNG=1, BIP=0 */
> > +		-MAX127_FULL_RANGE,	/* RNG=1, BIP=1 */
> > +	};
> > +
> > +	*val = min_input_map[rng_bip];
> > +	return 0;
> > +}
> > +
> > +static int max127_read_max(struct max127_data *data, int channel, long *val)
> > +{
> > +	u8 rng_bip = (data->ctrl_byte[channel] >> 2) & 3;
> > +	static const int max_input_map[4] = {
> > +		MAX127_HALF_RANGE,	/* RNG=0, BIP=0 */
> > +		MAX127_HALF_RANGE,	/* RNG=0, BIP=1 */
> > +		MAX127_FULL_RANGE,	/* RNG=1, BIP=0 */
> > +		MAX127_FULL_RANGE,	/* RNG=1, BIP=1 */
> > +	};
> > +
> > +	*val = max_input_map[rng_bip];
> > +	return 0;
> > +}
> > +
> > +static int max127_write_min(struct max127_data *data, int channel, long val)
> > +{
> > +	u8 ctrl;
> > +
> > +	ctrl = data->ctrl_byte[channel];
> > +	if (val <= -MAX127_FULL_RANGE) {
> > +		ctrl |= (MAX127_CTRL_RNG | MAX127_CTRL_BIP);
> > +	} else if (val < 0) {
> > +		ctrl |= MAX127_CTRL_BIP;
> > +		ctrl &= ~MAX127_CTRL_RNG;
> > +	} else {
> > +		ctrl &= ~MAX127_CTRL_BIP;
> > +	}
> > +	data->ctrl_byte[channel] = ctrl;
> 
> Needs mutex protection to avoid parallel writes (which might mess up
> ctrl_byte[channel]).
> 
> > +
> > +	return 0;
> > +}
> > +
> > +static int max127_write_max(struct max127_data *data, int channel, long val)
> > +{
> > +	if (val >= MAX127_FULL_RANGE)
> > +		data->ctrl_byte[channel] |= MAX127_CTRL_RNG;
> > +	else
> > +		data->ctrl_byte[channel] &= ~MAX127_CTRL_RNG;
> > +
> Same here, to avoid interaction with write_min (which might otherwise
> read ctrl and modify it at the same time as this function).

Thanks for pointing it out, and both functions are protected by mutex in
v4.


Cheers,

Tao

> 
> > +	return 0;
> > +}
> > +
> > +static umode_t max127_is_visible(const void *_data,
> > +				 enum hwmon_sensor_types type,
> > +				 u32 attr, int channel)
> > +{
> > +	if (type == hwmon_in) {
> > +		switch (attr) {
> > +		case hwmon_in_input:
> > +			return 0444;
> > +
> > +		case hwmon_in_min:
> > +		case hwmon_in_max:
> > +			return 0644;
> > +
> > +		default:
> > +			break;
> > +		}
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static int max127_read(struct device *dev, enum hwmon_sensor_types type,
> > +			u32 attr, int channel, long *val)
> > +{
> > +	int status;
> > +	struct max127_data *data = dev_get_drvdata(dev);
> > +
> > +	if (type != hwmon_in)
> > +		return -EOPNOTSUPP;
> > +
> > +	switch (attr) {
> > +	case hwmon_in_input:
> > +		status = max127_read_input(data, channel, val);
> > +		break;
> > +
> > +	case hwmon_in_min:
> > +		status = max127_read_min(data, channel, val);
> > +		break;
> > +
> > +	case hwmon_in_max:
> > +		status = max127_read_max(data, channel, val);
> > +		break;
> > +
> > +	default:
> > +		status = -EOPNOTSUPP;
> > +		break;
> > +	}
> > +
> > +	return status;
> > +}
> > +
> > +static int max127_write(struct device *dev, enum hwmon_sensor_types type,
> > +			u32 attr, int channel, long val)
> > +{
> > +	int status;
> > +	struct max127_data *data = dev_get_drvdata(dev);
> > +
> > +	if (type != hwmon_in)
> > +		return -EOPNOTSUPP;
> > +
> > +	switch (attr) {
> > +	case hwmon_in_min:
> > +		status = max127_write_min(data, channel, val);
> > +		break;
> > +
> > +	case hwmon_in_max:
> > +		status = max127_write_max(data, channel, val);
> > +		break;
> > +
> > +	default:
> > +		status = -EOPNOTSUPP;
> > +		break;
> > +	}
> > +
> > +	return status;
> > +}
> > +
> > +static const struct hwmon_ops max127_hwmon_ops = {
> > +	.is_visible = max127_is_visible,
> > +	.read = max127_read,
> > +	.write = max127_write,
> > +};
> > +
> > +static const struct hwmon_channel_info *max127_info[] = {
> > +	HWMON_CHANNEL_INFO(in,
> > +			   HWMON_I_INPUT | HWMON_I_MIN | HWMON_I_MAX,
> > +			   HWMON_I_INPUT | HWMON_I_MIN | HWMON_I_MAX,
> > +			   HWMON_I_INPUT | HWMON_I_MIN | HWMON_I_MAX,
> > +			   HWMON_I_INPUT | HWMON_I_MIN | HWMON_I_MAX,
> > +			   HWMON_I_INPUT | HWMON_I_MIN | HWMON_I_MAX,
> > +			   HWMON_I_INPUT | HWMON_I_MIN | HWMON_I_MAX,
> > +			   HWMON_I_INPUT | HWMON_I_MIN | HWMON_I_MAX,
> > +			   HWMON_I_INPUT | HWMON_I_MIN | HWMON_I_MAX),
> > +	NULL,
> > +};
> > +
> > +static const struct hwmon_chip_info max127_chip_info = {
> > +	.ops = &max127_hwmon_ops,
> > +	.info = max127_info,
> > +};
> > +
> > +static int max127_probe(struct i2c_client *client,
> > +			const struct i2c_device_id *id)
> > +{
> > +	int i;
> > +	struct device *hwmon_dev;
> > +	struct max127_data *data;
> > +	struct device *dev = &client->dev;
> > +
> > +	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
> > +	if (!data)
> > +		return -ENOMEM;
> > +
> > +	data->client = client;
> > +	mutex_init(&data->lock);
> > +	for (i = 0; i < ARRAY_SIZE(data->ctrl_byte); i++)
> > +		data->ctrl_byte[i] = (MAX127_CTRL_START |
> > +				      MAX127_SET_CHANNEL(i));
> > +
> > +	hwmon_dev = devm_hwmon_device_register_with_info(dev, client->name,
> > +							 data,
> > +							 &max127_chip_info,
> > +							 NULL);
> > +
> > +	return PTR_ERR_OR_ZERO(hwmon_dev);
> > +}
> > +
> > +static const struct i2c_device_id max127_id[] = {
> > +	{ "max127", 0 },
> > +	{ }
> > +};
> > +MODULE_DEVICE_TABLE(i2c, max127_id);
> > +
> > +static struct i2c_driver max127_driver = {
> > +	.class		= I2C_CLASS_HWMON,
> > +	.driver = {
> > +		.name	= "max127",
> > +	},
> > +	.probe		= max127_probe,
> > +	.id_table	= max127_id,
> > +};
> > +
> > +module_i2c_driver(max127_driver);
> > +
> > +MODULE_LICENSE("GPL");
> > +MODULE_AUTHOR("Mike Choi <mikechoi@fb.com>");
> > +MODULE_AUTHOR("Tao Ren <rentao.bupt@gmail.com>");
> > +MODULE_DESCRIPTION("MAX127 Hardware Monitoring driver");