Date:	Wed, 22 Jul 2015 08:33:16 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Punit Agrawal <punit.agrawal@....com>, linux-pm@...r.kernel.org
CC:	lm-sensors@...sensors.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org, Jean Delvare <jdelvare@...e.de>,
	Sudeep Holla <sudeep.holla@....com>
Subject: Re: [PATCH 6/9] hwmon: Support sensors exported via ARM SCP interface

On 07/22/2015 07:02 AM, Punit Agrawal wrote:
> Create a driver to add support for SoC sensors exported by the System
> Control Processor (SCP) via the System Control and Power Interface
> (SCPI). The supported sensor types is one of voltage, temperature,
> current, and power.
>
> The sensor labels and values provided by the SCP are exported via the
> hwmon sysfs interface.
>
> Signed-off-by: Punit Agrawal <punit.agrawal@....com>
> Cc: Jean Delvare <jdelvare@...e.de>
> Cc: Guenter Roeck <linux@...ck-us.net>
> Cc: Sudeep Holla <sudeep.holla@....com>
> ---
>   drivers/hwmon/Kconfig      |   8 ++
>   drivers/hwmon/Makefile     |   1 +
>   drivers/hwmon/scpi-hwmon.c | 212 +++++++++++++++++++++++++++++++++++++++++++++

Please also provide Documentation/hwmon/scpi-hwmon.

>   3 files changed, 221 insertions(+)
>   create mode 100644 drivers/hwmon/scpi-hwmon.c
>
> diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
> index 4943c3c..f5e0862 100644
> --- a/drivers/hwmon/Kconfig
> +++ b/drivers/hwmon/Kconfig
> @@ -1551,6 +1551,14 @@ config SENSORS_VEXPRESS
>   	  the ARM Ltd's Versatile Express platform. It can provide wide
>   	  range of information like temperature, power, energy.
>
> +config SENSORS_ARM_SCPI
> +	tristate "ARM SCPI Sensors"
> +	depends on ARM_SCPI_PROTOCOL
> +	help
> +	  This driver provides support for hardware sensors available on
> +	  the ARM Ltd's SCP based platforms. It can provide temperature

can provide or provides ?
> +	  and voltage for range of devices on the SoC.

current, power ?

> +
>   config SENSORS_VIA_CPUTEMP
>   	tristate "VIA CPU temperature sensor"
>   	depends on X86
> diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
> index 8aba87f..4961710 100644
> --- a/drivers/hwmon/Makefile
> +++ b/drivers/hwmon/Makefile
> @@ -150,6 +150,7 @@ obj-$(CONFIG_SENSORS_TMP421)	+= tmp421.o
>   obj-$(CONFIG_SENSORS_TWL4030_MADC)+= twl4030-madc-hwmon.o
>   obj-$(CONFIG_SENSORS_V2M_JUNO)	+= v2m-juno.o
>   obj-$(CONFIG_SENSORS_VEXPRESS)	+= vexpress.o
> +obj-$(CONFIG_SENSORS_ARM_SCPI)	+= scpi-hwmon.o
>   obj-$(CONFIG_SENSORS_VIA_CPUTEMP)+= via-cputemp.o
>   obj-$(CONFIG_SENSORS_VIA686A)	+= via686a.o
>   obj-$(CONFIG_SENSORS_VT1211)	+= vt1211.o
> diff --git a/drivers/hwmon/scpi-hwmon.c b/drivers/hwmon/scpi-hwmon.c
> new file mode 100644
> index 0000000..dd0a6f1
> --- /dev/null
> +++ b/drivers/hwmon/scpi-hwmon.c
> @@ -0,0 +1,212 @@
> +/*
> + * System Control and Power Interface(SCPI) based hwmon sensor driver
> + *
> + * Copyright (C) 2015 ARM Ltd.
> + * Punit Agrawal <punit.agrawal@....com>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed "as is" WITHOUT ANY WARRANTY of any
> + * kind, whether express or implied; without even the implied warranty
> + * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + */
> +
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

Not needed since there are no pr_xxx() messages in this driver.

> +
> +#include <linux/hwmon.h>
> +#include <linux/module.h>
> +#include <linux/platform_device.h>
> +#include <linux/scpi_protocol.h>
> +#include <linux/slab.h>
> +#include <linux/sysfs.h>
> +
> +static struct scpi_ops *scpi_ops;
> +
This variable should be kept in a local data structure (scpi_sensors).

> +struct sensor_dev {
> +	struct scpi_sensor_info info;
> +	struct device_attribute dev_attr_input;
> +	struct device_attribute dev_attr_label;
> +	char input[20];
> +	char label[20];
> +};
> +
> +struct scpi_sensors {
> +	int num_volt;
> +	int num_temp;
> +	int num_current;
> +	int num_power;

num_volt, num_temp, num_current, and num_power are not used
outside the probe function and are thus not needed in this structure.

> +	struct sensor_dev *device;

'device' is a bit misleading here. It might be better to use
something like sensor_data (and maybe struct sensor_data),
or just 'data'.

> +	struct device *hwdev;

hwdev is not used and thus not needed in this structure.

> +};
> +struct scpi_sensors scpi_sensors;

This variable should be allocated in the probe function (and either case not be global).

> +
> +static int scpi_read_sensor(struct sensor_dev *sensor, u32 *value)
> +{
> +	int ret;
> +
> +	ret = scpi_ops->sensor_get_value(sensor->info.sensor_id, value);
> +	if (ret)
> +		return ret;
> +
> +	return 0;

This can be reduced to
	return scpi_ops->sensor_get_value(sensor->info.sensor_id, value);

which makes me wonder if the function is that useful to start with,
but I leave that up to you.

> +}
> +
> +/* hwmon callback functions */
> +static ssize_t
> +scpi_hwmon_show_sensor(struct device *dev,
> +		       struct device_attribute *attr, char *buf)

_hwmon in the function names do not really add value.

> +{
> +	struct sensor_dev *sensor;
> +	u32 value;
> +	int ret;
> +
> +	sensor = container_of(attr, struct sensor_dev, dev_attr_input);
> +
> +	ret = scpi_read_sensor(sensor, &value);
> +	if (ret) {
> +		dev_warn(dev, "error (ret=%d) reading sensor (id=%u) value\n",
> +			 ret, sensor->info.sensor_id);
> +		return 0;

Please no error message (it can get noisy), and return the error.

> +	}
> +
> +	return sprintf(buf, "%u\n", value);
> +}
> +
> +static ssize_t
> +scpi_hwmon_show_label(struct device *dev,
> +		      struct device_attribute *attr, char *buf)
> +{
> +	struct sensor_dev *sensor;
> +
> +	sensor = container_of(attr, struct sensor_dev, dev_attr_label);
> +
> +	return sprintf(buf, "%s\n", sensor->info.name);
> +}
> +
> +struct attribute *scpi_attrs[24] = { 0 };

This creates an unnecessary (hard) limit on the number of supported
sensors (12). I would suggest to allocate the array based on the number
of reported sensors.

> +struct attribute_group scpi_group;
> +const struct attribute_group *scpi_groups[2] = { 0 };

Please move those variables into struct scpi_sensors.

Note that you don't have to initialize globale variables with 0,
and that globale variables should be static. It does not matter here
since you should not have those variables to start with (they should
be in struct scpi_sensors and be allocated), just mentioning it.

> +
> +static int scpi_hwmon_probe(struct platform_device *pdev)
> +{
> +	u16 sensors, i;
> +	int ret;
> +
> +	scpi_ops = get_scpi_ops();
> +	if (!scpi_ops)
> +		return -EPROBE_DEFER;
> +
Is this appropriate ? I am a bit concerned that we might get a lot
of "requests probe deferral" if the underlying infrastructure is
not there at all.

> +	ret = scpi_ops->sensor_get_capability(&sensors);
> +	if (ret)
> +		return ret;
> +
> +	scpi_sensors.device = devm_kcalloc(&pdev->dev, sensors,
> +				   sizeof(*scpi_sensors.device), GFP_KERNEL);

What if sensors == 0 ?

It might be useful to introduce a local variable
	struct device *dev = &pdev->dev;
and use it in this function.

> +	if (!scpi_sensors.device)
> +		return -ENOMEM;
> +
> +	dev_info(&pdev->dev, "Found %d sensors\n", sensors);

Please drop this message and the other info messages below (too noisy).
If you think you need those messages for debugging, make it dev_dbg().

> +	for (i = 0; i < sensors; i++) {
> +		struct sensor_dev *dev = &scpi_sensors.device[i];
> +
> +		ret = scpi_ops->sensor_get_info(i, &dev->info);
> +		if (ret) {
> +			dev_info(&pdev->dev,
> +				 "Error ret=%d when querying for sensor %d\n",
> +				 ret, i);

If this is an error, it should be dev_err().

> +			return ret;
> +		}
> +
> +		dev_info(&pdev->dev, "Probed \'%s\' sensor.\n",
> +			 dev->info.name);
> +
> +		switch (dev->info.class) {
> +		case TEMPERATURE:
> +			snprintf(dev->input, 20,

Can you use sizeof() to determine the string length ?

> +				 "temp%d_input", scpi_sensors.num_temp);
> +			snprintf(dev->label, 20,
> +				 "temp%d_label", scpi_sensors.num_temp);
> +			scpi_sensors.num_temp++;

temp sensor numbering starts with 1.

> +			break;
> +		case VOLTAGE:
> +			snprintf(dev->input, 20,
> +				 "in%d_input", scpi_sensors.num_volt);
> +			snprintf(dev->label, 20,
> +				 "in%d_label", scpi_sensors.num_volt);
> +			scpi_sensors.num_volt++;
> +			break;
> +		case CURRENT:
> +			snprintf(dev->input, 20,
> +				 "curr%d_input", scpi_sensors.num_current);
> +			snprintf(dev->label, 20,
> +				 "curr%d_label", scpi_sensors.num_current);
> +			scpi_sensors.num_current++;

current sensor numbering starts with 1.

> +			break;
> +		case POWER:
> +			snprintf(dev->input, 20,
> +				 "power%d_input", scpi_sensors.num_power);
> +			snprintf(dev->label, 20,
> +				 "power%d_label", scpi_sensors.num_power);
> +			scpi_sensors.num_power++;

power sensor numbering starts with 1.

> +			break;
> +		default:
> +			break;
> +		}
> +
> +		dev->dev_attr_input.attr.mode = S_IRUGO;
> +		dev->dev_attr_input.store = NULL;

kcalloc() initializes the allocated memory, so this assignment is unnecessary.

> +		dev->dev_attr_input.show = scpi_hwmon_show_sensor;
> +		dev->dev_attr_input.attr.name = dev->input;
> +
> +		dev->dev_attr_label.attr.mode = S_IRUGO;
> +		dev->dev_attr_label.store = NULL;

Same as above.

> +		dev->dev_attr_label.show = scpi_hwmon_show_label;
> +		dev->dev_attr_label.attr.name = dev->label;
> +
> +		scpi_attrs[i << 1] = &dev->dev_attr_input.attr;
> +		scpi_attrs[(i << 1) + 1] = &dev->dev_attr_label.attr;

You need to call sysfs_attr_init() for each of the attributes.

> +	}
> +
> +	scpi_group.attrs = scpi_attrs;
> +	scpi_groups[0] = &scpi_group;
> +
> +	scpi_sensors.hwdev = devm_hwmon_device_register_with_groups(&pdev->dev,
> +				    "scpi_sensors", &scpi_sensors, scpi_groups);

Please allocate scpi_sensors and pass a pointer to it.
All local variables should be kept in scpi_sensors (and can then be accessed
with dev_get_drvdata).

> +
> +	if (IS_ERR(scpi_sensors.hwdev)) {
> +		dev_err(&pdev->dev, "Error registering scpi_sensors hwmon device\n");
> +		return PTR_ERR(scpi_sensors.hwdev);
> +	}
> +
> +	dev_info(&pdev->dev, "SCPI hwmon driver initialised.\n");

Please consider just returning
	return PTR_ERR_OR_ZERO(hwdev);
without the noise.

> +	return 0;
> +}
> +
> +static int scpi_hwmon_remove(struct platform_device *pdev)
> +{
> +	scpi_ops = NULL;
> +	return 0;
> +}

Not needed.

> +
> +static const struct of_device_id scpi_of_match[] = {
> +	{.compatible = "arm,scpi-sensors"},
> +	{},
> +};
> +
> +static struct platform_driver scpi_hwmon_platdrv = {
> +	.driver = {
> +		.name	= "scpi-hwmon",
> +		.owner	= THIS_MODULE,
> +		.of_match_table = scpi_of_match,
> +	},
> +	.probe		= scpi_hwmon_probe,
> +	.remove	= scpi_hwmon_remove,
> +};
> +module_platform_driver(scpi_hwmon_platdrv);
> +
> +MODULE_AUTHOR("Punit Agrawal <punit.agrawal@....com>");
> +MODULE_DESCRIPTION("ARM SCPI HWMON interface driver");
> +MODULE_LICENSE("GPL v2");
>

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