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Date:   Tue, 16 Apr 2019 12:52:55 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Ruslan Babayev <ruslan@...ayev.com>
Cc:     xe-linux-external@...co.com, Jean Delvare <jdelvare@...e.com>,
        linux-hwmon@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] hwmon: (pmbus) add support for output voltage
 registers

On Tue, Apr 16, 2019 at 11:36:16AM -0700, Ruslan Babayev wrote:
> Registers VOUT_COMMAND, VOUT_MARGIN_HIGH and VOUT_MARGIN_LOW are
> described in PMBUS Spec Part II Rev 1.2. Exposing them in the PMBUS
> core allows the drivers to turn them on with a corresponding
> PMBUS_HAVE_VOUT_... flags.
> 
> Cc: xe-linux-external@...co.com
> Signed-off-by: Ruslan Babayev <ruslan@...ayev.com>
> ---
>  drivers/hwmon/pmbus/pmbus.h      |   7 ++
>  drivers/hwmon/pmbus/pmbus_core.c | 183 +++++++++++++++++++++++++++++++
>  2 files changed, 190 insertions(+)
> 
> diff --git a/drivers/hwmon/pmbus/pmbus.h b/drivers/hwmon/pmbus/pmbus.h
> index 1d24397d36ec..723648b3da36 100644
> --- a/drivers/hwmon/pmbus/pmbus.h
> +++ b/drivers/hwmon/pmbus/pmbus.h
> @@ -223,6 +223,9 @@ enum pmbus_regs {
>   * OPERATION
>   */
>  #define PB_OPERATION_CONTROL_ON		BIT(7)
> +#define PB_OPERATION_MARGIN_HIGH	BIT(5)
> +#define PB_OPERATION_MARGIN_LOW		BIT(4)
> +#define PB_OPERATION_ACT_ON_FAULT	BIT(3)
>  
>  /*
>   * CAPABILITY
> @@ -291,6 +294,7 @@ enum pmbus_fan_mode { percent = 0, rpm };
>  /*
>   * STATUS_VOUT, STATUS_INPUT
>   */
> +#define PB_VOLTAGE_MAX_WARNING		BIT(3)
>  #define PB_VOLTAGE_UV_FAULT		BIT(4)
>  #define PB_VOLTAGE_UV_WARNING		BIT(5)
>  #define PB_VOLTAGE_OV_WARNING		BIT(6)
> @@ -371,6 +375,9 @@ enum pmbus_sensor_classes {
>  #define PMBUS_HAVE_STATUS_VMON	BIT(19)
>  #define PMBUS_HAVE_PWM12	BIT(20)
>  #define PMBUS_HAVE_PWM34	BIT(21)
> +#define PMBUS_HAVE_VOUT_COMMAND		BIT(22)
> +#define PMBUS_HAVE_VOUT_MARGIN_HIGH	BIT(23)
> +#define PMBUS_HAVE_VOUT_MARGIN_LOW	BIT(24)
>  
>  #define PMBUS_PAGE_VIRTUAL	BIT(31)
>  
> diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
> index 2e2b5851139c..f35b239961e3 100644
> --- a/drivers/hwmon/pmbus/pmbus_core.c
> +++ b/drivers/hwmon/pmbus/pmbus_core.c
> @@ -89,6 +89,14 @@ struct pmbus_label {
>  #define to_pmbus_label(_attr) \
>  	container_of(_attr, struct pmbus_label, attribute)
>  
> +struct pmbus_operation {
> +	char name[PMBUS_NAME_SIZE];	/* sysfs label name */
> +	struct sensor_device_attribute attribute;
> +	u8 page;
> +};
> +#define to_pmbus_operation(_attr) \
> +	container_of(_attr, struct pmbus_operation, attribute)
> +
>  struct pmbus_data {
>  	struct device *dev;
>  	struct device *hwmon_dev;
> @@ -1004,6 +1012,65 @@ static ssize_t pmbus_show_label(struct device *dev,
>  	return snprintf(buf, PAGE_SIZE, "%s\n", label->label);
>  }
>  
> +static ssize_t pmbus_show_operation(struct device *dev,
> +				    struct device_attribute *devattr, char *buf)
> +{
> +	struct sensor_device_attribute *attr = to_sensor_dev_attr(devattr);
> +	struct pmbus_operation *operation = to_pmbus_operation(attr);
> +	struct i2c_client *client = to_i2c_client(dev->parent);
> +	int ret;
> +
> +	ret = pmbus_read_byte_data(client, operation->page, PMBUS_OPERATION);
> +	if (ret < 0)
> +		return ret;
> +
> +	if (ret & PB_OPERATION_CONTROL_ON) {
> +		if (ret & PB_OPERATION_MARGIN_HIGH)
> +			return snprintf(buf, PAGE_SIZE, "high\n");
> +		else if (ret & PB_OPERATION_MARGIN_LOW)
> +			return snprintf(buf, PAGE_SIZE, "low\n");
> +		else
> +			return snprintf(buf, PAGE_SIZE, "on\n");
> +	} else {
> +			return snprintf(buf, PAGE_SIZE, "off\n");
> +	}
> +}
> +
> +static ssize_t pmbus_set_operation(struct device *dev,
> +				   struct device_attribute *devattr,
> +				   const char *buf, size_t count)
> +{
> +	struct sensor_device_attribute *attr = to_sensor_dev_attr(devattr);
> +	struct pmbus_operation *operation = to_pmbus_operation(attr);
> +	struct i2c_client *client = to_i2c_client(dev->parent);
> +	int ret;
> +	u8 val;
> +
> +	/*
> +	 * sysfs_streq() doesn't need the \n's, but we add them so the strings
> +	 * will be shared with pmbus_show_operation() above.
> +	 */

Saving a few bytes of data in the driver is not worth such limitations. 
I would not want to have to deal with users sending "echo -n on" to the
driver and complain that it doesn't work.

> +	if (sysfs_streq(buf, "on\n"))
> +		val = PB_OPERATION_CONTROL_ON;
> +	else if (sysfs_streq(buf, "off\n"))
> +		val = 0;
> +	else if (sysfs_streq(buf, "high\n"))
> +		val = PB_OPERATION_CONTROL_ON | PB_OPERATION_ACT_ON_FAULT |
> +		      PB_OPERATION_MARGIN_HIGH;
> +	else if (sysfs_streq(buf, "low\n"))
> +		val = PB_OPERATION_CONTROL_ON | PB_OPERATION_ACT_ON_FAULT |
> +		      PB_OPERATION_MARGIN_LOW;
> +	else
> +		return -EINVAL;
> +
> +	ret = pmbus_write_byte_data(client, operation->page,
> +				    PMBUS_OPERATION, val);
> +	if (ret < 0)
> +		return ret;
> +
> +	return count;
> +}
> +
I am not convinced that it is a good idea to implement this as sysfs
attributes. It is notmally only used in manufacturing, and there the
registers can be acccessed directly.

Either case, we can not implement this in the pmbus driver as generic code.
Operation commands are notoriously implemented with slight differences across
different devices. It would also probably be more appropriate to implement
as regulator, since it affects setting voltages, not limits.

>  static int pmbus_add_attribute(struct pmbus_data *data, struct attribute *attr)
>  {
>  	if (data->num_attributes >= data->max_attributes - 1) {
> @@ -1143,6 +1210,29 @@ static int pmbus_add_label(struct pmbus_data *data,
>  	return pmbus_add_attribute(data, &a->attr);
>  }
>  
> +static int pmbus_add_operation(struct pmbus_data *data, const char *name,
> +			       int seq, int page)
> +{
> +	struct pmbus_operation *operation;
> +	struct sensor_device_attribute *a;
> +
> +	operation = devm_kzalloc(data->dev, sizeof(*operation), GFP_KERNEL);
> +	if (!operation)
> +		return -ENOMEM;
> +
> +	a = &operation->attribute;
> +
> +	snprintf(operation->name, sizeof(operation->name), "%s%d_operation",
> +		 name, seq);
> +
> +	operation->page = page;
> +
> +	pmbus_attr_init(a, operation->name, S_IRUGO | S_IWUSR,
> +			pmbus_show_operation, pmbus_set_operation, seq);
> +
> +	return pmbus_add_attribute(data, &a->dev_attr.attr);
> +}
> +
>  /*
>   * Search for attributes. Allocate sensors, booleans, and labels as needed.
>   */
> @@ -1901,6 +1991,93 @@ static int pmbus_add_fan_attributes(struct i2c_client *client,
>  	return 0;
>  }
>  
> +static const struct pmbus_limit_attr vout_cmd_limit_attrs[] = {
> +	{
> +		.reg = PMBUS_VOUT_MAX,
> +		.attr = "max",
> +		.alarm = "max_alarm",
> +		.sbit = PB_VOLTAGE_MAX_WARNING,
> +	}
> +};
> +
> +static const struct pmbus_sensor_attr vout_attributes[] = {
> +	{
> +		.reg = PMBUS_VOUT_COMMAND,
> +		.class = PSC_VOLTAGE_OUT,
> +		.label = "command",

Bad name for a label.

> +		.paged = true,
> +		.func = PMBUS_HAVE_VOUT_COMMAND,
> +		.sfunc = PMBUS_HAVE_STATUS_VOUT,
> +		.sbase = PB_STATUS_VOUT_BASE,
> +		.gbit = PB_STATUS_VOUT_OV,
> +		.limit = vout_cmd_limit_attrs,
> +		.nlimit = ARRAY_SIZE(vout_cmd_limit_attrs),
> +	}, {
> +		.reg = PMBUS_VOUT_MARGIN_HIGH,
> +		.class = PSC_VOLTAGE_OUT,
> +		.label = "margin_high",
> +		.paged = true,
> +		.func = PMBUS_HAVE_VOUT_MARGIN_HIGH,
> +	}, {
> +		.reg = PMBUS_VOUT_MARGIN_LOW,
> +		.class = PSC_VOLTAGE_OUT,
> +		.label = "margin_low",
> +		.paged = true,
> +		.func = PMBUS_HAVE_VOUT_MARGIN_LOW,
> +	}
> +};
> +
> +static int pmbus_add_vout_attrs(struct i2c_client *client,
> +				struct pmbus_data *data,
> +				const char *name,
> +				const struct pmbus_sensor_attr *attr,
> +				int nattrs)
> +{
> +	const struct pmbus_driver_info *info = data->info;
> +	struct pmbus_sensor *base;
> +	int i, ret, index, page, pages;
> +
> +	index = 1;
> +	for (page = 0; page < info->pages; page++) {
> +		if (!pmbus_check_byte_register(client, page, PMBUS_OPERATION))
> +			continue;
> +		ret = pmbus_add_operation(data, name, index, page);
> +		if (ret)
> +			return ret;
> +		index++;
> +	}
> +
> +	for (i = 0; i < nattrs; i++) {
> +		index = 1;
> +		pages = attr->paged ? info->pages : 1;
> +		for (page = 0; page < pages; page++) {
> +			if (!(info->func[page] & attr->func))
> +				continue;
> +
> +			if (!pmbus_check_word_register(client, page, attr->reg))
> +				continue;
> +
> +			base = pmbus_add_sensor(data, name, attr->label, index,
> +						page, attr->reg, attr->class,
> +						true, false, true);
> +			if (!base)
> +				return -ENOMEM;
> +
> +			if (attr->sfunc) {
> +				ret = pmbus_add_limit_attrs(client, data, info,
> +							    name, index, page,
> +							    base, attr);
> +				if (ret < 0)
> +					return ret;
> +			}
> +
> +			index++;
> +		}
> +		attr++;
> +	}
> +	return 0;
> +}
> +
>  static int pmbus_find_attributes(struct i2c_client *client,
>  				 struct pmbus_data *data)
>  {
> @@ -1912,6 +2089,12 @@ static int pmbus_find_attributes(struct i2c_client *client,
>  	if (ret)
>  		return ret;
>  
> +	/* Output Voltage sensors */
> +	ret = pmbus_add_vout_attrs(client, data, "out", vout_attributes,
> +				   ARRAY_SIZE(vout_attributes));
> +	if (ret)
> +		return ret;
> +

The sensors you are adding are not output voltage sensors. They are not
sensors in the first place, and should probably not be reported as sensor
values. And setting voltages as limits is really not appropriate.

>  	/* Current sensors */
>  	ret = pmbus_add_sensor_attrs(client, data, "curr", current_attributes,
>  				     ARRAY_SIZE(current_attributes));
> -- 
> 2.17.1
> 

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