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

[Guenter Roeck <groeck@google.com>]

On Tue, May 7, 2024 at 8:30 AM Mario Limonciello
<mario.limonciello@amd.com> wrote:
>
> 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;
>

NACK. This is a static function. Callers are well known. If speed is
NULL this code deserves to crash.

> 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.
>

Again, this is a static function. The caller is in full control of the
parameter range, and those error checks should be unnecessary to start
with.

I am not going to review the rest of the driver. Drop all unnecessary
range checks and resubmit.

Guenter

> > +
> > +     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");
> >
>