Message-ID: <20180328170018.GC25325@roeck-us.net>
Date:   Wed, 28 Mar 2018 10:00:18 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Tim Harvey <tharvey@...eworks.com>
Cc:     Lee Jones <lee.jones@...aro.org>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Mark Brown <broonie@...nel.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Wim Van Sebroeck <wim@...ana.be>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-hwmon@...r.kernel.org,
        linux-input@...r.kernel.org, linux-watchdog@...r.kernel.org
Subject: Re: [PATCH v3 3/4] hwmon: add Gateworks System Controller support

On Wed, Mar 28, 2018 at 08:14:02AM -0700, Tim Harvey wrote:
> The Gateworks System Controller has a hwmon sub-component that exposes
> up to 16 ADC's, some of which are temperature sensors, others which are
> voltage inputs. The ADC configuration (register mapping and name) is
> configured via device-tree and varies board to board.
> 
> Cc: Guenter Roeck <linux@...ck-us.net>
> Signed-off-by: Tim Harvey <tharvey@...eworks.com>
> ---
> v3:
> - add voltage_raw input type and supporting fields
> - add channel validation to is_visible function
> - remove unnecessary channel validation from read/write functions
> 
> v2:
> - change license comment style
> - remove DEBUG
> - simplify regmap_bulk_read err check
> - remove break after returns in switch statement
> - fix fan setpoint buffer address
> - remove unnecessary parens
> - consistently use struct device *dev pointer
> - change license/comment block
> - add validation for hwmon child node props
> - move parsing of of to own function
> - use strlcpy to ensure null termination
> - fix static array sizes and removed unnecessary initializers
> - dynamically allocate channels
> - fix fan input label
> - support platform data
> - fixed whitespace issues
> 
>  drivers/hwmon/Kconfig                   |   9 +
>  drivers/hwmon/Makefile                  |   1 +
>  drivers/hwmon/gsc-hwmon.c               | 368 ++++++++++++++++++++++++++++++++

This will require a matching Documentation/hwmon/gsc-hwmon to explain supported
attributes.

>  include/linux/platform_data/gsc_hwmon.h |  43 ++++
>  4 files changed, 421 insertions(+)
>  create mode 100644 drivers/hwmon/gsc-hwmon.c
>  create mode 100644 include/linux/platform_data/gsc_hwmon.h
> 
> diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
> index 7ad0176..85d9aa3 100644
> --- a/drivers/hwmon/Kconfig
> +++ b/drivers/hwmon/Kconfig
> @@ -475,6 +475,15 @@ config SENSORS_F75375S
>  	  This driver can also be built as a module.  If so, the module
>  	  will be called f75375s.
>  
> +config SENSORS_GSC
> +        tristate "Gateworks System Controller ADC"
> +        depends on MFD_GATEWORKS_GSC
> +        help
> +          Support for the Gateworks System Controller A/D converters.
> +
> +	  To compile this driver as a module, choose M here:
> +	  the module will be called gsc-hwmon.
> +
>  config SENSORS_MC13783_ADC
>          tristate "Freescale MC13783/MC13892 ADC"
>          depends on MFD_MC13XXX
> diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
> index 0fe489f..835a536 100644
> --- a/drivers/hwmon/Makefile
> +++ b/drivers/hwmon/Makefile
> @@ -69,6 +69,7 @@ obj-$(CONFIG_SENSORS_G760A)	+= g760a.o
>  obj-$(CONFIG_SENSORS_G762)	+= g762.o
>  obj-$(CONFIG_SENSORS_GL518SM)	+= gl518sm.o
>  obj-$(CONFIG_SENSORS_GL520SM)	+= gl520sm.o
> +obj-$(CONFIG_SENSORS_GSC)	+= gsc-hwmon.o
>  obj-$(CONFIG_SENSORS_GPIO_FAN)	+= gpio-fan.o
>  obj-$(CONFIG_SENSORS_HIH6130)	+= hih6130.o
>  obj-$(CONFIG_SENSORS_ULTRA45)	+= ultra45_env.o
> diff --git a/drivers/hwmon/gsc-hwmon.c b/drivers/hwmon/gsc-hwmon.c
> new file mode 100644
> index 0000000..10da46f
> --- /dev/null
> +++ b/drivers/hwmon/gsc-hwmon.c
> @@ -0,0 +1,368 @@
> +/* SPDX-License-Identifier: GPL-2.0
> + *
> + * Copyright (C) 2018 Gateworks Corporation
> + *
> + * This driver registers Linux HWMON attributes for GSC ADC's
> + */
> +#include <linux/hwmon.h>
> +#include <linux/hwmon-sysfs.h>
> +#include <linux/mfd/gsc.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/platform_device.h>
> +#include <linux/regmap.h>
> +#include <linux/slab.h>
> +
> +#include <linux/platform_data/gsc_hwmon.h>
> +
> +#define GSC_HWMON_MAX_TEMP_CH	16
> +#define GSC_HWMON_MAX_IN_CH	16
> +#define GSC_HWMON_MAX_FAN_CH	6
> +
> +struct gsc_hwmon_data {
> +	struct gsc_dev *gsc;
> +	struct device *dev;
> +	struct gsc_hwmon_platform_data *pdata;
> +	const struct gsc_hwmon_channel *temp_ch[GSC_HWMON_MAX_TEMP_CH];
> +	const struct gsc_hwmon_channel *in_ch[GSC_HWMON_MAX_IN_CH];
> +	const struct gsc_hwmon_channel *fan_ch[GSC_HWMON_MAX_FAN_CH];
> +	u32 temp_config[GSC_HWMON_MAX_TEMP_CH + 1];
> +	u32 in_config[GSC_HWMON_MAX_IN_CH + 1];
> +	u32 fan_config[GSC_HWMON_MAX_FAN_CH + 1];
> +	struct hwmon_channel_info temp_info;
> +	struct hwmon_channel_info in_info;
> +	struct hwmon_channel_info fan_info;
> +	const struct hwmon_channel_info *info[4];
> +	struct hwmon_chip_info chip;
> +	int vreference;
> +	int resolution;
> +};
> +
> +static int
> +gsc_hwmon_read(struct device *dev, enum hwmon_sensor_types type, u32 attr,
> +	       int channel, long *val)
> +{
> +	struct gsc_hwmon_data *hwmon = dev_get_drvdata(dev);
> +	struct gsc_hwmon_platform_data *pdata = hwmon->pdata;
> +	const struct gsc_hwmon_channel *ch;
> +	int sz, ret;
> +	u8 buf[3];
> +
> +	dev_dbg(dev, "%s type=%d attr=%d channel=%d\n", __func__, type, attr,
> +		channel);
> +	switch (type) {
> +	case hwmon_in:
> +		ch = hwmon->in_ch[channel];
> +		break;
> +	case hwmon_temp:
> +		ch = hwmon->temp_ch[channel];
> +		break;
> +	case hwmon_fan:
> +		ch = hwmon->fan_ch[channel];
> +		break;
> +	default:
> +		return -EOPNOTSUPP;
> +	}
> +
> +	sz = (ch->type == type_voltage) ? 3 : 2;
> +	ret = regmap_bulk_read(hwmon->gsc->regmap_hwmon, ch->reg, buf, sz);
> +	if (ret)
> +		return ret;
> +
> +	*val = 0;
> +	while (sz-- > 0)
> +		*val |= (buf[sz] << (8*sz));

Please use spaces before and after operators.

> +
> +	switch (ch->type) {
> +	case type_temperature:
> +		if ((type == hwmon_temp) && *val > 0x8000)

Please no unnecessary ( ).

Is there ever a situation where ch->type == type_temperature and type !=
hwmon_temp ? Wouldn't that be a bug ?

> +			*val -= 0xffff;
> +		break;
> +	case type_voltage_raw:
> +		/* scale based on ref voltage and resolution */
> +		if (pdata->vreference && pdata->resolution) {
> +			*val *= pdata->vreference;
> +			*val /= pdata->resolution;
> +		}
> +		/* scale based on optional voltage divider */
> +		if (ch->vdiv[0] && ch->vdiv[1]) {
> +			*val *= (ch->vdiv[0] + ch->vdiv[1]);
> +			*val /= ch->vdiv[1];
> +		}

This accepts both types of scaling. Is that intentional ?

I don't see any protection against overflows. What if pdata->vreference is
larger than 256 on a system with sizeof(long) == 4 and the raw voltage
as reported by the chip is 0xffffff ?

> +		/* adjust by offset */
> +		*val += ch->voffset;

Similar to the above, this can result in an overflow on systems with
sizeof(long) == 4.

> +		break;

There should be a default case as well as 'case type_voltage:'
with a break; statement and a comment indicating that no adjustment
is needed.

> +	}
> +
> +	return 0;
> +}
> +
> +static int
> +gsc_hwmon_read_string(struct device *dev, enum hwmon_sensor_types type,
> +		      u32 attr, int channel, const char **buf)
> +{
> +	struct gsc_hwmon_data *hwmon = dev_get_drvdata(dev);
> +
> +	dev_dbg(dev, "%s type=%d attr=%d channel=%d\n", __func__, type, attr,
> +		channel);

I seriously wonder if all those dev_dbg() statements add value.

> +	switch (type) {
> +	case hwmon_in:
> +		*buf = hwmon->in_ch[channel]->name;
> +		break;
> +	case hwmon_temp:
> +		*buf = hwmon->temp_ch[channel]->name;
> +		break;
> +	case hwmon_fan:
> +		*buf = hwmon->fan_ch[channel]->name;
> +		break;
> +	default:
> +		return -ENOTSUPP;
> +	}
> +
> +	return 0;
> +}
> +
> +static int
> +gsc_hwmon_write(struct device *dev, enum hwmon_sensor_types type, u32 attr,
> +		int channel, long val)
> +{
> +	struct gsc_hwmon_data *hwmon = dev_get_drvdata(dev);
> +	u8 buf[2];
> +
> +	dev_dbg(dev, "%s type=%d attr=%d channel=%d\n", __func__, type, attr,
> +		channel);
> +	switch (type) {
> +	case hwmon_fan:
> +		buf[0] = val & 0xff;
> +		buf[1] = (val >> 8) & 0xff;
> +		return regmap_bulk_write(hwmon->gsc->regmap_hwmon,
> +					 hwmon->fan_ch[channel]->reg, buf, 2);

fanX_input reports the fan speed. By its nature, a fan speed is not writeable.
I have no idea what this is supposed to achieve, but whatever it is, it is wrong.

Please stick with the ABI.

> +	default:
> +		break;
> +	}
> +
> +	return -EOPNOTSUPP;
> +}
> +
> +static umode_t
> +gsc_hwmon_is_visible(const void *_data, enum hwmon_sensor_types type, u32 attr,
> +		     int ch)
> +{
> +	const struct gsc_hwmon_data *hwmon = _data;
> +	struct device *dev = hwmon->gsc->dev;
> +	umode_t mode = 0;
> +
> +	switch (type) {
> +	case hwmon_fan:
> +		if (ch >= GSC_HWMON_MAX_FAN_CH)
> +			return -EOPNOTSUPP;

Can that ever happen ?

> +		mode = S_IRUGO;
> +		if (attr == hwmon_fan_input)
> +			mode |= S_IWUSR;

fanX_input is a read-only attribute per ABI.

> +		break;
> +	case hwmon_temp:
> +		if (ch >= GSC_HWMON_MAX_TEMP_CH)
> +			return -EOPNOTSUPP;

Can that ever happen ?

> +		mode = S_IRUGO;
> +		break;
> +	case hwmon_in:
> +		if (ch >= GSC_HWMON_MAX_IN_CH)
> +			return -EOPNOTSUPP;

Can that ever happen ?

> +		mode = S_IRUGO;
> +		break;
> +	default:
> +		return -EOPNOTSUPP;
> +	}
> +	dev_dbg(dev, "%s type=%d attr=%d ch=%d mode=0x%x\n", __func__, type,
> +		attr, ch, mode);
> +
> +	return mode;
> +}
> +
> +static const struct hwmon_ops gsc_hwmon_ops = {
> +	.is_visible = gsc_hwmon_is_visible,
> +	.read = gsc_hwmon_read,
> +	.read_string = gsc_hwmon_read_string,
> +	.write = gsc_hwmon_write,
> +};
> +
> +static struct gsc_hwmon_platform_data *
> +gsc_hwmon_get_devtree_pdata(struct device *dev)
> +{
> +	struct gsc_hwmon_platform_data *pdata;
> +	struct gsc_hwmon_channel *ch;
> +	struct fwnode_handle *child;
> +	const char *type;
> +	int nchannels;
> +
> +	nchannels = device_get_child_node_count(dev);
> +	dev_dbg(dev, "channels=%d\n", nchannels);
> +	if (nchannels == 0)
> +		return ERR_PTR(-ENODEV);
> +
> +	pdata = devm_kzalloc(dev,
> +			     sizeof(*pdata) + nchannels * sizeof(*ch),
> +			     GFP_KERNEL);
> +	if (!pdata)
> +		return ERR_PTR(-ENOMEM);
> +	ch = (struct gsc_hwmon_channel *)(pdata + 1);
> +	pdata->channels = ch;
> +	pdata->nchannels = nchannels;
> +
> +	device_property_read_u32(dev, "gw,reference-voltage",
> +				 &pdata->vreference);
> +	device_property_read_u32(dev, "gw,resolution", &pdata->resolution);
> +
> +	/* allocate structures for channels and count instances of each type */
> +	device_for_each_child_node(dev, child) {
> +		if (fwnode_property_read_string(child, "label", &ch->name)) {
> +			dev_err(dev, "channel without label\n");
> +			fwnode_handle_put(child);
> +			return ERR_PTR(-EINVAL);
> +		}
> +		if (fwnode_property_read_u32(child, "reg", &ch->reg)) {
> +			dev_err(dev, "channel without reg\n");
> +			fwnode_handle_put(child);
> +			return ERR_PTR(-EINVAL);
> +		}
> +		if (fwnode_property_read_string(child, "type", &type)) {
> +			dev_err(dev, "channel without type\n");
> +			fwnode_handle_put(child);
> +			return ERR_PTR(-EINVAL);
> +		}
> +		if (!strcasecmp(type, "gw,hwmon-temperature"))
> +			ch->type = type_temperature;
> +		else if (!strcasecmp(type, "gw,hwmon-voltage"))
> +			ch->type = type_voltage;
> +		else if (!strcasecmp(type, "gw,hwmon-voltage-raw"))
> +			ch->type = type_voltage_raw;
> +		else if (!strcasecmp(type, "gw,hwmon-fan"))
> +			ch->type = type_fan;
> +		else {
> +			dev_err(dev, "channel without type\n");
> +			fwnode_handle_put(child);
> +			return ERR_PTR(-EINVAL);
> +		}
> +
> +		fwnode_property_read_u32(child, "gw,voltage-offset",
> +			&ch->voffset);

Note that while it is technically ok to keep voltages internally in mV,
devicetree will likely require specificayion in uV. For accuracy, it might be
better to perform any calculations on that base and convert to mV for display
purposes.

> +		fwnode_property_read_u32_array(child, "gw,voltage-divider",
> +			ch->vdiv, ARRAY_SIZE(ch->vdiv));
> +		dev_dbg(dev, "of: reg=0x%02x type=%d %s\n", ch->reg, ch->type,
> +			ch->name);
> +		ch++;
> +	}
> +
> +	return pdata;
> +}
> +
> +static int gsc_hwmon_probe(struct platform_device *pdev)
> +{
> +	struct gsc_dev *gsc = dev_get_drvdata(pdev->dev.parent);
> +	struct device *dev = &pdev->dev;
> +	struct gsc_hwmon_platform_data *pdata = dev_get_platdata(dev);
> +	struct gsc_hwmon_data *hwmon;
> +	int i, i_in, i_temp, i_fan;
> +
> +	if (!pdata) {
> +		pdata = gsc_hwmon_get_devtree_pdata(dev);
> +		if (IS_ERR(pdata))
> +			return PTR_ERR(pdata);
> +	}
> +
> +	hwmon = devm_kzalloc(dev, sizeof(*hwmon), GFP_KERNEL);
> +	if (!hwmon)
> +		return -ENOMEM;
> +	hwmon->gsc = gsc;
> +	hwmon->pdata = pdata;
> +
> +	for (i = 0, i_in = 0, i_temp = 0, i_fan = 0;
> +	     i < hwmon->pdata->nchannels; i++) {
> +		const struct gsc_hwmon_channel *ch = &pdata->channels[i];
> +
> +		if (ch->reg > GSC_HWMON_MAX_REG) {
> +			dev_err(dev, "invalid reg: 0x%02x\n", ch->reg);
> +			return -EINVAL;
> +		}
> +		switch (ch->type) {
> +		case type_temperature:
> +			if (i_temp == GSC_HWMON_MAX_TEMP_CH) {
> +				dev_err(dev, "too many temp channels\n");
> +				return -EINVAL;
> +			}
> +			hwmon->temp_ch[i_temp] = ch;
> +			hwmon->temp_config[i_temp] = HWMON_T_INPUT |
> +						     HWMON_T_LABEL;
> +			i_temp++;
> +			break;
> +		case type_voltage:
> +		case type_voltage_raw:
> +			if (i_in == GSC_HWMON_MAX_IN_CH) {
> +				dev_err(dev, "too many voltage channels\n");
> +				return -EINVAL;
> +			}
> +			hwmon->in_ch[i_in] = ch;
> +			hwmon->in_config[i_in] =
> +				HWMON_I_INPUT | HWMON_I_LABEL;
> +			i_in++;
> +			break;
> +		case type_fan:
> +			if (i_fan == GSC_HWMON_MAX_FAN_CH) {
> +				dev_err(dev, "too many voltage channels\n");
> +				return -EINVAL;
> +			}
> +			hwmon->fan_ch[i_fan] = ch;
> +			hwmon->fan_config[i_fan] =
> +				HWMON_F_INPUT | HWMON_F_LABEL;
> +			i_fan++;
> +			break;
> +		default:
> +			dev_err(dev, "invalid type: %d\n", ch->type);
> +			return -EINVAL;
> +		}
> +		dev_dbg(dev, "pdata: reg=0x%02x type=%d %s\n", ch->reg,
> +			ch->type, ch->name);
> +	}
> +
> +	/* terminate channel config lists */
> +	hwmon->temp_config[i_temp] = 0;
> +	hwmon->in_config[i_in] = 0;
> +	hwmon->fan_config[i_fan] = 0;

'hwmon' was alocated with devm_kzalloc(). Initializing any of its members with 0
is unnecessary.

> +
> +	/* setup config structures */
> +	hwmon->chip.ops = &gsc_hwmon_ops;
> +	hwmon->chip.info = hwmon->info;
> +	hwmon->info[0] = &hwmon->temp_info;
> +	hwmon->info[1] = &hwmon->in_info;
> +	hwmon->info[2] = &hwmon->fan_info;
> +	hwmon->temp_info.type = hwmon_temp;
> +	hwmon->temp_info.config = hwmon->temp_config;
> +	hwmon->in_info.type = hwmon_in;
> +	hwmon->in_info.config = hwmon->in_config;
> +	hwmon->fan_info.type = hwmon_fan;
> +	hwmon->fan_info.config = hwmon->fan_config;
> +
> +	hwmon->dev = devm_hwmon_device_register_with_info(dev,
> +							  KBUILD_MODNAME, hwmon,
> +							  &hwmon->chip, NULL);
> +	return PTR_ERR_OR_ZERO(hwmon->dev);
> +}
> +
> +static const struct of_device_id gsc_hwmon_of_match[] = {
> +	{ .compatible = "gw,gsc-hwmon", },
> +	{}
> +};
> +
> +static struct platform_driver gsc_hwmon_driver = {
> +	.driver = {
> +		.name = KBUILD_MODNAME,
> +		.of_match_table = gsc_hwmon_of_match,
> +	},
> +	.probe = gsc_hwmon_probe,
> +};
> +
> +module_platform_driver(gsc_hwmon_driver);
> +
> +MODULE_AUTHOR("Tim Harvey <tharvey@...eworks.com>");
> +MODULE_DESCRIPTION("GSC hardware monitor driver");
> +MODULE_LICENSE("GPL v2");
> diff --git a/include/linux/platform_data/gsc_hwmon.h b/include/linux/platform_data/gsc_hwmon.h
> new file mode 100644
> index 0000000..5e59846
> --- /dev/null
> +++ b/include/linux/platform_data/gsc_hwmon.h
> @@ -0,0 +1,43 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _GSC_HWMON_H
> +#define _GSC_HWMON_H
> +
> +enum gsc_hwmon_type {
> +	type_temperature,
> +	type_voltage,
> +	type_voltage_raw,
> +	type_fan,
> +};
> +
> +/**
> + * struct gsc_hwmon_channel - configuration parameters
> + * @reg:  I2C register offset
> + * @type: channel type
> + * @name: channel name
> + * @voffset: voltage offset (mV)
> + * @vdiv: voltage divider array (2 resistor values in ohms)
> + */
> +struct gsc_hwmon_channel {
> +	unsigned int reg;
> +	unsigned int type;
> +	const char *name;
> +	unsigned int voffset;

It is interesting that only positive offset values are supported.
Is that intentional ?

> +	unsigned int vdiv[2];
> +};
> +
> +/**
> + * struct gsc_hwmon_platform_data - platform data for gsc_hwmon driver
> + * @channels:	pointer to array of gsc_hwmon_channel structures
> + *		describing channels
> + * @nchannels:	number of elements in @channels array
> + * @vreference: voltage reference (mV)
> + * @resolution: ADC resolution

Resolution in what ?

> + */
> +struct gsc_hwmon_platform_data {
> +	const struct gsc_hwmon_channel *channels;
> +	int nchannels;
> +	unsigned int resolution;
> +	unsigned int vreference;
> +};
> +
> +#endif
> -- 
> 2.7.4
> 

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