Re: [PATCH 1/2] hwmon: (max127) Add Maxim MAX127 hardware monitoring driver

Tao Ren
2020-11-18T01:55:36Z

Hi Guenter,

Thanks for pointing out these problems. I'm working on the comments and
will send out v2 soon.

Cheers,

Tao

On Mon, Nov 16, 2020 at 09:13:52PM -0800, Guenter Roeck wrote:
> On Mon, Nov 16, 2020 at 05:09:43PM -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>
> > ---
> > drivers/hwmon/Kconfig | 9 ++
> > drivers/hwmon/Makefile | 1 +
> > drivers/hwmon/max127.c | 286 +++++++++++++++++++++++++++++++++++++++++
> > 3 files changed, 296 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..df74a95bcf28
> > --- /dev/null
> > +++ b/drivers/hwmon/max127.c
> > @@ -0,0 +1,286 @@
> > +// 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>
> > +#include <linux/i2c.h>
> > +#include <linux/init.h>
> > +#include <linux/module.h>
> > +#include <linux/sysfs.h>
> > +
> > +/* MAX127 Control Byte. */
> > +#define MAX127_CTRL_START BIT(7)
> > +#define MAX127_CTRL_SEL_OFFSET 4
>
> That would better be named _SHIFT.
>
> > +#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_OFFSET))
>
> () around MAX127_CTRL_SEL_OFFSET is unnecessary.
>
> > +
> > +#define MAX127_INPUT_LIMIT 10 /* 10V */
> > +
> > +/*
> > + * 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).
> > + */
> > +#define MAX127_DATA1_SHIFT 4
> > +
> > +struct max127_data {
> > + struct mutex lock;
> > + struct i2c_client *client;
> > + int input_limit;
> > + u8 ctrl_byte[MAX127_NUM_CHANNELS];
> > +};
> > +
> > +static int max127_select_channel(struct max127_data *data, int channel)
> > +{
> > + int status;
> > + struct i2c_client *client = data->client;
> > + struct i2c_msg msg = {
> > + .addr = client->addr,
> > + .flags = 0,
> > + .len = 1,
> > + .buf = &data->ctrl_byte[channel],
> > + };
> > +
> > + status = i2c_transfer(client->adapter, &msg, 1);
> > + if (status != 1)
> > + return status;
> > +
>
> Other drivers assume that this function can return 0. Please
> take that into account as well.
>
> > + return 0;
> > +}
> > +
> > +static int max127_read_channel(struct max127_data *data, int channel, u16 *vin)
> > +{
> > + int status;
> > + u8 i2c_data[2];
> > + struct i2c_client *client = data->client;
> > + struct i2c_msg msg = {
> > + .addr = client->addr,
> > + .flags = I2C_M_RD,
> > + .len = 2,
> > + .buf = i2c_data,
> > + };
> > +
> > + status = i2c_transfer(client->adapter, &msg, 1);
> > + if (status != 1)
> > + return status;
>
> Same as above.
>
> > +
> > + *vin = ((i2c_data[0] << 8) | i2c_data[1]) >> MAX127_DATA1_SHIFT;
>
> THis seems wrong. D4..D11 end up in but 8..15, and D0..D3 end up in bit
> 0..3. Seems to me the upper byte should be left shifted 4 bit.
> The result then needs to be scaled to mV (see below).
>
> Also, for consistency I would suggest to either use () for both
> parts of the logical or operation or for none.
>
> > + return 0;
> > +}
> > +
> > +static ssize_t max127_input_show(struct device *dev,
> > + struct device_attribute *dev_attr,
> > + char *buf)
> > +{
> > + u16 vin;
> > + int status;
> > + struct max127_data *data = dev_get_drvdata(dev);
> > + struct sensor_device_attribute *attr = to_sensor_dev_attr(dev_attr);
> > +
> > + if (mutex_lock_interruptible(&data->lock))
> > + return -ERESTARTSYS;
>
> I don't think the _interruptible is warranted in this driver.
>
> > +
> > + status = max127_select_channel(data, attr->index);
> > + if (status)
> > + goto exit;
> > +
> > + status = max127_read_channel(data, attr->index, &vin);
> > + if (status)
> > + goto exit;
> > +
> > + status = sprintf(buf, "%u", vin);
>
> This is not correct. The ABI expects values in milli-Volt, and per datasheet
> the values need to be scaled depending on polarity and range settings (see
> table 3 in datasheet). Also, if the range includes negative numbers,
> the reported voltage can obviously be negative. That means %u (and u16)
> can not be correct. "Transfer Function" in the datasheet describes how to
> convert/scale the received data.
>
> > +
> > +exit:
> > + mutex_unlock(&data->lock);
> > + return status;
> > +}
> > +
> > +static ssize_t max127_range_show(struct device *dev,
> > + struct device_attribute *dev_attr,
> > + char *buf)
> > +{
> > + u8 ctrl, rng_bip;
> > + struct max127_data *data = dev_get_drvdata(dev);
> > + struct sensor_device_attribute_2 *attr = to_sensor_dev_attr_2(dev_attr);
> > + int rng_type = attr->nr; /* 0 for min, 1 for max */
> > + int channel = attr->index;
> > + int full = data->input_limit;
> > + int half = full / 2;
> > + int range_table[4][2] = {
> > + [0] = {0, half}, /* RNG=0, BIP=0 */
> > + [1] = {-half, half}, /* RNG=0, BIP=1 */
> > + [2] = {0, full}, /* RNG=1, BIP=0 */
> > + [3] = {-full, full}, /* RNG=1, BIP=1 */
> > + };
>
> This can be a static const table. The variables 'full' and 'half'
> are effectively constants and not really needed.
>
> > +
> > + if (mutex_lock_interruptible(&data->lock))
> > + return -ERESTARTSYS;
> > + ctrl = data->ctrl_byte[channel];
> > + mutex_unlock(&data->lock);
>
> This lock is only needed because "ctrl" is written piece by piece.
> I would suggest to rewrite the store function to write ctrl atomically.
> Then the lock here is no longer needed.
>
> > +
> > + rng_bip = (ctrl >> 2) & 3;
> > + return sprintf(buf, "%d", range_table[rng_bip][rng_type]);
> > +}
> > +
> > +static void max127_set_range(struct max127_data *data, int channel)
> > +{
> > + data->ctrl_byte[channel] |= MAX127_CTRL_RNG;
> > +}
> > +
> > +static void max127_clear_range(struct max127_data *data, int channel)
> > +{
> > + data->ctrl_byte[channel] &= ~MAX127_CTRL_RNG;
> > +}
> > +
> > +static void max127_set_polarity(struct max127_data *data, int channel)
> > +{
> > + data->ctrl_byte[channel] |= MAX127_CTRL_BIP;
> > +}
> > +
> > +static void max127_clear_polarity(struct max127_data *data, int channel)
> > +{
> > + data->ctrl_byte[channel] &= ~MAX127_CTRL_BIP;
> > +}
> > +
> > +static ssize_t max127_range_store(struct device *dev,
> > + struct device_attribute *devattr,
> > + const char *buf,
> > + size_t count)
> > +{
> > + struct max127_data *data = dev_get_drvdata(dev);
> > + struct sensor_device_attribute_2 *attr = to_sensor_dev_attr_2(devattr);
> > + int rng_type = attr->nr; /* 0 for min, 1 for max */
> > + int channel = attr->index;
> > + int full = data->input_limit;
> > + int half = full / 2;
> > + long input, output;
> > +
> > + if (kstrtol(buf, 0, &input))
> > + return -EINVAL;
> > +
> > + if (rng_type == 0) { /* min input */
> > + if (input <= -full)
> > + output = -full;
> > + else if (input < 0)
> > + output = -half;
> > + else
> > + output = 0;
> > + } else { /* max input */
> > + output = (input >= full) ? full : half;
> > + }
> > +
>
> With the _info API, I would suggest to separate min and max functions.
> This would both simplify the code and make it easier to read and
> review.
>
> > + if (mutex_lock_interruptible(&data->lock))
> > + return -ERESTARTSYS;
>
> This should be rewritten to update "ctrl" in one step.
> Something like
>
> u8 ctrl;
> ...
> ctrl = data->ctrl_byte[channel];
> if (output == -MAX127_INPUT_LIMIT)
> ctrl |= MAX127_CTRL_RNG | MAX127_CTRL_BIP;
> else if (output == -half)
> ctrl |= MAX127_CTRL_BIP;
> ctrl &= ~MAX127_CTRL_RNG;
> else if (output == 0)
> ctrl &= ~MAX127_CTRL_BIP;
> else lf (output == half)
> ctrl &= ~MAX127_CTRL_RNG;
> else
> ctrl |= MAX127_CTRL_RNG;
>
> data->ctrl_byte[channel] = ctrl;
>
> I would suggest to separate the min and max functions, though.
>
> > +
> > + if (output == -full) {
> > + max127_set_polarity(data, channel);
> > + max127_set_range(data, channel);
> > + } else if (output == -half) {
> > + max127_set_polarity(data, channel);
> > + max127_clear_range(data, channel);
> > + } else if (output == 0) {
> > + max127_clear_polarity(data, channel);
> > + } else if (output == half) {
> > + max127_clear_range(data, channel);
> > + } else {
> > + max127_set_range(data, channel);
> > + }
> > +
> > + mutex_unlock(&data->lock);
> > +
> > + return count;
> > +}
> > +
> > +#define MAX127_SENSOR_DEV_ATTR_DEF(ch) \
> > + static SENSOR_DEVICE_ATTR_RO(in##ch##_input, max127_input, ch); \
> > + static SENSOR_DEVICE_ATTR_2_RW(in##ch##_min, max127_range, 0, ch); \
> > + static SENSOR_DEVICE_ATTR_2_RW(in##ch##_max, max127_range, 1, ch)
> > +
> > +MAX127_SENSOR_DEV_ATTR_DEF(0);
> > +MAX127_SENSOR_DEV_ATTR_DEF(1);
> > +MAX127_SENSOR_DEV_ATTR_DEF(2);
> > +MAX127_SENSOR_DEV_ATTR_DEF(3);
> > +MAX127_SENSOR_DEV_ATTR_DEF(4);
> > +MAX127_SENSOR_DEV_ATTR_DEF(5);
> > +MAX127_SENSOR_DEV_ATTR_DEF(6);
> > +MAX127_SENSOR_DEV_ATTR_DEF(7);
> > +
> > +#define MAX127_SENSOR_DEVICE_ATTR(ch) \
> > + &sensor_dev_attr_in##ch##_input.dev_attr.attr, \
> > + &sensor_dev_attr_in##ch##_min.dev_attr.attr, \
> > + &sensor_dev_attr_in##ch##_max.dev_attr.attr
> > +
> > +static struct attribute *max127_attrs[] = {
> > + MAX127_SENSOR_DEVICE_ATTR(0),
> > + MAX127_SENSOR_DEVICE_ATTR(1),
> > + MAX127_SENSOR_DEVICE_ATTR(2),
> > + MAX127_SENSOR_DEVICE_ATTR(3),
> > + MAX127_SENSOR_DEVICE_ATTR(4),
> > + MAX127_SENSOR_DEVICE_ATTR(5),
> > + MAX127_SENSOR_DEVICE_ATTR(6),
> > + MAX127_SENSOR_DEVICE_ATTR(7),
> > + NULL,
> > +};
> > +
> > +ATTRIBUTE_GROUPS(max127);
> > +
> > +static const struct attribute_group max127_attr_groups = {
> > + .attrs = max127_attrs,
> > +};
> > +
> > +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);
> > + data->input_limit = MAX127_INPUT_LIMIT;
>
> What is the point of input_limit ? It is never modified.
> Why not use MAX127_INPUT_LIMIT directly where needed ?
>
> > + 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_groups(dev,
> > + client->name, data, max127_groups);
>
> Please use the devm_hwmon_device_register_with_info() API.
>
> Thanks,
> Guenter
>
> > +
> > + 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");
> > --
> > 2.17.1
> >