Re: [PATCH 1/2] hwmon: add ChromeOS EC driver

[Mario Limonciello <mario.limonciello@amd.com>]

On 5/7/2024 08:57, Thomas Weißschuh wrote:
> The ChromeOS Embedded Controller exposes fan speed and temperature
> readings.
> Expose this data through the hwmon subsystem.
> 
> The driver is designed to be probed via the cros_ec mfd device.
> 
> Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> ---
>   Documentation/hwmon/cros_ec_hwmon.rst |  26 ++++
>   Documentation/hwmon/index.rst         |   1 +
>   MAINTAINERS                           |   8 +
>   drivers/hwmon/Kconfig                 |  11 ++
>   drivers/hwmon/Makefile                |   1 +
>   drivers/hwmon/cros_ec_hwmon.c         | 279 ++++++++++++++++++++++++++++++++++
>   6 files changed, 326 insertions(+)
> 
> diff --git a/Documentation/hwmon/cros_ec_hwmon.rst b/Documentation/hwmon/cros_ec_hwmon.rst
> new file mode 100644
> index 000000000000..aeb88c79d11b
> --- /dev/null
> +++ b/Documentation/hwmon/cros_ec_hwmon.rst
> @@ -0,0 +1,26 @@
> +.. SPDX-License-Identifier: GPL-2.0-or-later
> +
> +Kernel driver cros_ec_hwmon
> +===========================
> +
> +Supported chips:
> +
> +  * ChromeOS embedded controllers connected via LPC
> +
> +    Prefix: 'cros_ec'
> +
> +    Addresses scanned: -
> +
> +Author:
> +
> +  - Thomas Weißschuh <linux@weissschuh.net>
> +
> +Description
> +-----------
> +
> +This driver implements support for hardware monitoring commands exposed by the
> +ChromeOS embedded controller used in Chromebooks and other devices.
> +
> +The channel labels exposed via hwmon are retrieved from the EC itself.
> +
> +Fan and temperature readings are supported.
> diff --git a/Documentation/hwmon/index.rst b/Documentation/hwmon/index.rst
> index 1ca7a4fe1f8f..355a83e66928 100644
> --- a/Documentation/hwmon/index.rst
> +++ b/Documentation/hwmon/index.rst
> @@ -57,6 +57,7 @@ Hardware Monitoring Kernel Drivers
>      coretemp
>      corsair-cpro
>      corsair-psu
> +   cros_ec_hwmon
>      da9052
>      da9055
>      dell-smm-hwmon
> diff --git a/MAINTAINERS b/MAINTAINERS
> index c23fda1aa1f0..aa5689169eca 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -4988,6 +4988,14 @@ S:	Maintained
>   F:	Documentation/devicetree/bindings/sound/google,cros-ec-codec.yaml
>   F:	sound/soc/codecs/cros_ec_codec.*
>   
> +CHROMEOS EC HARDWARE MONITORING
> +M:	Thomas Weißschuh <thomas@weissschuh.net>
> +L:	chrome-platform@lists.linux.dev
> +L:	linux-hwmon@vger.kernel.org
> +S:	Maintained
> +F:	Documentation/hwmon/chros_ec_hwmon.rst
> +F:	drivers/hwmon/cros_ec_hwmon.c
> +
>   CHROMEOS EC SUBDRIVERS
>   M:	Benson Leung <bleung@chromium.org>
>   R:	Guenter Roeck <groeck@chromium.org>
> diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
> index 83945397b6eb..c1284d42697f 100644
> --- a/drivers/hwmon/Kconfig
> +++ b/drivers/hwmon/Kconfig
> @@ -506,6 +506,17 @@ config SENSORS_CORSAIR_PSU
>   	  This driver can also be built as a module. If so, the module
>   	  will be called corsair-psu.
>   
> +config SENSORS_CROS_EC
> +	tristate "ChromeOS Embedded Controller sensors"
> +	depends on MFD_CROS_EC_DEV
> +	default MFD_CROS_EC_DEV
> +	help
> +	  If you say yes here you get support for ChromeOS Embedded Controller
> +	  sensors.
> +
> +	  This driver can also be built as a module. If so, the module
> +	  will be called cros_ec_hwmon.
> +
>   config SENSORS_DRIVETEMP
>   	tristate "Hard disk drives with temperature sensors"
>   	depends on SCSI && ATA
> diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
> index 5c31808f6378..8519a6b36c00 100644
> --- a/drivers/hwmon/Makefile
> +++ b/drivers/hwmon/Makefile
> @@ -64,6 +64,7 @@ obj-$(CONFIG_SENSORS_CHIPCAP2) += chipcap2.o
>   obj-$(CONFIG_SENSORS_CORETEMP)	+= coretemp.o
>   obj-$(CONFIG_SENSORS_CORSAIR_CPRO) += corsair-cpro.o
>   obj-$(CONFIG_SENSORS_CORSAIR_PSU) += corsair-psu.o
> +obj-$(CONFIG_SENSORS_CROS_EC)	+= cros_ec_hwmon.o
>   obj-$(CONFIG_SENSORS_DA9052_ADC)+= da9052-hwmon.o
>   obj-$(CONFIG_SENSORS_DA9055)+= da9055-hwmon.o
>   obj-$(CONFIG_SENSORS_DELL_SMM)	+= dell-smm-hwmon.o
> diff --git a/drivers/hwmon/cros_ec_hwmon.c b/drivers/hwmon/cros_ec_hwmon.c
> new file mode 100644
> index 000000000000..9588df202a74
> --- /dev/null
> +++ b/drivers/hwmon/cros_ec_hwmon.c
> @@ -0,0 +1,279 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + *  ChromesOS EC driver for hwmon
> + *
> + *  Copyright (C) 2024 Thomas Weißschuh <linux@weissschuh.net>
> + */
> +
> +#include <linux/device.h>
> +#include <linux/hwmon.h>
> +#include <linux/kernel.h>
> +#include <linux/mod_devicetable.h>
> +#include <linux/module.h>
> +#include <linux/platform_device.h>
> +#include <linux/platform_data/cros_ec_commands.h>
> +#include <linux/platform_data/cros_ec_proto.h>
> +#include <linux/units.h>
> +
> +#define DRV_NAME	"cros-ec-hwmon"
> +
> +struct cros_ec_hwmon_priv {
> +	struct cros_ec_device *cros_ec;
> +	u8 thermal_version;
> +	const char *temp_sensor_names[EC_TEMP_SENSOR_ENTRIES + EC_TEMP_SENSOR_B_ENTRIES];
> +};
> +
> +static int cros_ec_hwmon_read_fan_speed(struct cros_ec_device *cros_ec, u8 index, u16 *speed)
> +{
> +	int ret;
> +	u16 data;
> +
> +	if (index >= EC_FAN_SPEED_ENTRIES)
> +		return -ENODEV;

I could see an argument that this should be -EINVAL as 
EC_FAN_SPEED_ENTRIES is hardcoded in the driver and "index" was passed 
into the function.

> +
> +	ret = cros_ec->cmd_readmem(cros_ec, EC_MEMMAP_FAN + index * 2, 2, &data);
> +	if (ret < 0)
> +		return ret;
> +
> +	data = le16_to_cpu(data);
> +
> +	if (data == EC_FAN_SPEED_NOT_PRESENT)
> +		return -ENODEV;
> +
> +	*speed = data;

For safety purposes I think you should either do

if (speed)
	*speed = data;

Or have a check at the start of the function and return -EINVAL and 
throw up a warning if speed was NULL.

> +	return 0;
> +}
> +
> +static int cros_ec_hwmon_read_temp(struct cros_ec_device *cros_ec, u8 thermal_version,
> +				   u8 index, u8 *data)
> +{
> +	unsigned int offset;
> +	int ret;
> +
> +	if (thermal_version < 2 && index >= EC_TEMP_SENSOR_ENTRIES)
> +		return -ENODEV;
> +
> +	if (index >= EC_TEMP_SENSOR_ENTRIES + EC_TEMP_SENSOR_B_ENTRIES)
> +		return -ENODEV;

Like cros_ec_hwmon_read_fan_speed I have an opinion these should be -EINVAL.

> +
> +	if (index < EC_TEMP_SENSOR_ENTRIES)
> +		offset = EC_MEMMAP_TEMP_SENSOR + index;
> +	else
> +		offset = EC_MEMMAP_TEMP_SENSOR_B + index - EC_TEMP_SENSOR_ENTRIES;
> +
> +	ret = cros_ec->cmd_readmem(cros_ec, offset, 1, data);
> +	if (ret < 0)
> +		return ret;
> +

You should make sure that data isn't NULL before doing these checks:

> +	if (*data == EC_TEMP_SENSOR_NOT_PRESENT ||
> +	    *data == EC_TEMP_SENSOR_ERROR ||
> +	    *data == EC_TEMP_SENSOR_NOT_POWERED ||
> +	    *data == EC_TEMP_SENSOR_NOT_CALIBRATED)
> +		return -ENODEV;
> +
> +	return 0;
> +}
> +
> +static int cros_ec_hwmon_read(struct device *dev, enum hwmon_sensor_types type,
> +			      u32 attr, int channel, long *val)
> +{
> +	struct cros_ec_hwmon_priv *priv = dev_get_drvdata(dev);
> +	u16 speed;
> +	u8 temp;
> +	int ret = -ENODATA;

I feel it is better practice to add this as a 3rd clause than initialize 
the variable at the start of the function.

switch (type) {
case hwmon_fan:
	//do stuff
	break;
case hwmon_temp:
	// dot stuff
	break;
default:
	ret = -ENODATA;
}

return ret;

> +
> +	if (type == hwmon_fan) {
> +		ret = cros_ec_hwmon_read_fan_speed(priv->cros_ec, channel, &speed);
> +		if (ret == 0)
> +			*val = speed;
> +	} else if (type == hwmon_temp) {
> +		ret = cros_ec_hwmon_read_temp(priv->cros_ec, priv->thermal_version, channel, &temp);
> +		if (ret == 0)
> +			*val = kelvin_to_millicelsius((((long)temp) + EC_TEMP_SENSOR_OFFSET));
> +	}
> +
> +	return ret;
> +}
> +
> +static int cros_ec_hwmon_get_temp_sensor_info(struct cros_ec_device *cros_ec, u8 id,
> +					      struct ec_response_temp_sensor_get_info *resp)
> +{
> +	int ret;
> +	struct {
> +		struct cros_ec_command msg;
> +		union {
> +			struct ec_params_temp_sensor_get_info req;
> +			struct ec_response_temp_sensor_get_info resp;
> +		} __packed data;
> +	} __packed buf = {
> +		.msg = {
> +			.version = 0,
> +			.command = EC_CMD_TEMP_SENSOR_GET_INFO,
> +			.insize  = sizeof(buf.data.resp),
> +			.outsize = sizeof(buf.data.req),
> +		},
> +		.data.req.id = id,
> +	};
> +
> +	ret = cros_ec_cmd_xfer_status(cros_ec, &buf.msg);
> +	if (ret < 0)
> +		return ret;
> +
> +	*resp = buf.data.resp;

Make sure that resp isn't NULL.

> +	return 0;
> +}
> +
> +static int cros_ec_hwmon_read_string(struct device *dev, enum hwmon_sensor_types type,
> +				     u32 attr, int channel, const char **str)
> +{
> +	struct cros_ec_hwmon_priv *priv = dev_get_drvdata(dev);
> +	int ret = -ENODATA;

How about just drop the variable and then do below two comments:

> +
> +	if (type == hwmon_temp && attr == hwmon_temp_label) {
> +		*str = priv->temp_sensor_names[channel];
> +		ret = 0;
		return 0;
> +	}
> +
> +	return ret;
	return -ENODATA;
> +}
> +
> +static umode_t cros_ec_hwmon_is_visible(const void *data, enum hwmon_sensor_types type,
> +					u32 attr, int channel)
> +{
> +	const struct cros_ec_hwmon_priv *priv = data;
> +	u16 speed;
> +
> +	if (type == hwmon_fan) {
> +		if (cros_ec_hwmon_read_fan_speed(priv->cros_ec, channel, &speed) == 0)
> +			return 0444;
> +	} else if (type == hwmon_temp) {
> +		if (priv->temp_sensor_names[channel])
> +			return 0444;
> +	}
> +
> +	return 0;
> +}
> +
> +static const struct hwmon_channel_info * const cros_ec_hwmon_info[] = {
> +	HWMON_CHANNEL_INFO(fan,
> +			   HWMON_F_INPUT,
> +			   HWMON_F_INPUT,
> +			   HWMON_F_INPUT,
> +			   HWMON_F_INPUT),
> +	HWMON_CHANNEL_INFO(temp,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL,
> +			   HWMON_T_INPUT | HWMON_T_LABEL),
> +	NULL
> +};
> +
> +static const struct hwmon_ops cros_ec_hwmon_ops = {
> +	.read = cros_ec_hwmon_read,
> +	.read_string = cros_ec_hwmon_read_string,
> +	.is_visible = cros_ec_hwmon_is_visible,
> +};
> +
> +static const struct hwmon_chip_info cros_ec_hwmon_chip_info = {
> +	.ops = &cros_ec_hwmon_ops,
> +	.info = cros_ec_hwmon_info,
> +};
> +
> +static int cros_ec_hwmon_probe_temp_sensors(struct device *dev, struct cros_ec_hwmon_priv *priv)
> +{
> +	struct ec_response_temp_sensor_get_info info;
> +	size_t i;
> +	u8 temp;
> +	int ret;
> +
> +	ret = priv->cros_ec->cmd_readmem(priv->cros_ec, EC_MEMMAP_THERMAL_VERSION,
> +					 1, &priv->thermal_version);
> +	if (ret < 0)
> +		return ret;
> +
> +	if (!priv->thermal_version)
> +		return 0;

I'm a bit confused; why isn't this -ENODEV?  I would think that you 
don't want to have probe succeed and make devices if there isn't thermal 
support in the EC.

> +
> +	for (i = 0; i < ARRAY_SIZE(priv->temp_sensor_names); i++) {
> +		if (cros_ec_hwmon_read_temp(priv->cros_ec, priv->thermal_version, i, &temp) != 0)
> +			continue;
> +
> +		ret = cros_ec_hwmon_get_temp_sensor_info(priv->cros_ec, i, &info);
> +		if (ret < 0)
> +			continue;
> +
> +		priv->temp_sensor_names[i] = devm_kasprintf(dev, GFP_KERNEL, "%*s",
> +							    (int)sizeof(info.sensor_name),
> +							    info.sensor_name);
> +	}
> +
> +	return 0;
> +}
> +
> +static int cros_ec_hwmon_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct cros_ec_dev *ec_dev = dev_get_drvdata(dev->parent);
> +	struct cros_ec_device *cros_ec = ec_dev->ec_dev;
> +	struct cros_ec_hwmon_priv *priv;
> +	struct device *hwmon_dev;
> +	int ret;
> +
> +	BUILD_BUG_ON(ARRAY_SIZE(priv->temp_sensor_names) != 24);
> +
> +	/* Not every platform supports direct reads */
> +	if (!cros_ec->cmd_readmem)
> +		return -ENOTTY;
> +
> +	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
> +	if (!priv)
> +		return -ENOMEM;
> +
> +	priv->cros_ec = cros_ec;
> +
> +	ret = cros_ec_hwmon_probe_temp_sensors(dev, priv);
> +	if (ret < 0)
> +		return ret;
> +
> +	hwmon_dev = devm_hwmon_device_register_with_info(dev, "cros_ec", priv,
> +							 &cros_ec_hwmon_chip_info, NULL);
> +
> +	return PTR_ERR_OR_ZERO(hwmon_dev);
> +}
> +
> +static const struct platform_device_id cros_ec_hwmon_id[] = {
> +	{ DRV_NAME, 0 },
> +	{ }
> +};
> +
> +static struct platform_driver cros_ec_hwmon_driver = {
> +	.driver.name	= DRV_NAME,
> +	.probe		= cros_ec_hwmon_probe,
> +	.id_table	= cros_ec_hwmon_id,
> +};
> +module_platform_driver(cros_ec_hwmon_driver);
> +
> +MODULE_DEVICE_TABLE(platform, cros_ec_hwmon_id);
> +MODULE_DESCRIPTION("ChromeOS EC Hardware Monitoring Driver");
> +MODULE_AUTHOR("Thomas Weißschuh <linux@weissschuh.net");
> +MODULE_LICENSE("GPL");
>