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Date: Thu, 7 Oct 2021 19:33:54 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Alexandre Bailon <abailon@...libre.com>
Cc: "Zhang, Rui" <rui.zhang@...el.com>,
Daniel Lezcano <daniel.lezcano@...aro.org>,
Amit Kucheria <amitk@...nel.org>,
Linux PM <linux-pm@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
ben.tseng@...iatek.com, Kevin Hilman <khilman@...libre.com>,
Matthias Kaehlcke <mka@...omium.org>,
kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v2 2/2] thermal: add a virtual sensor to aggregate temperatures
On Thu, Oct 7, 2021 at 6:38 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Fri, Sep 17, 2021 at 9:25 AM Alexandre Bailon <abailon@...libre.com> wrote:
> >
> > This adds a virtual thermal sensor that reads temperature from
>
> This should be "virtual sensor driver" I suppose.
>
> > hardware sensor and return an aggregated temperature.
>
> "returns"
>
> Also wrapping it around a single hardware sensor makes a little sense
> AFAICS, so I guess you mean "multiple hardware sensors" here.
>
> > Currently, this supports three operations:
> > the minimum, maximum and average temperature.
>
> They are aggregation functions rather than "operations"
>
> >
> > Reported-by: kernel test robot <lkp@...el.com>
>
> This is new code, so what does it fix?
>
> > Signed-off-by: Alexandre Bailon <abailon@...libre.com>
> > ---
> > drivers/thermal/Kconfig | 8 +
> > drivers/thermal/Makefile | 1 +
> > drivers/thermal/virtual-thermal-sensor.h | 54 ++++
> > drivers/thermal/virtual_thermal_sensor.c | 350 +++++++++++++++++++++++
> > 4 files changed, 413 insertions(+)
> > create mode 100644 drivers/thermal/virtual-thermal-sensor.h
> > create mode 100644 drivers/thermal/virtual_thermal_sensor.c
> >
> > diff --git a/drivers/thermal/Kconfig b/drivers/thermal/Kconfig
> > index d7f44deab5b1d..20bc93c48f5b1 100644
> > --- a/drivers/thermal/Kconfig
> > +++ b/drivers/thermal/Kconfig
> > @@ -228,6 +228,14 @@ config THERMAL_MMIO
> > register or shared memory, is a potential candidate to work with this
> > driver.
> >
> > +config VIRTUAL_THERMAL
> > + tristate "Virtual thermal sensor driver"
>
> This should be "DT-based virtual thermal sensor driver" I think.
>
> > + depends on THERMAL_OF || COMPILE_TEST
> > + help
> > + This option enables the generic thermal sensor aggregator.
>
> "generic DT-based"
>
> > + This driver creates a thermal sensor that reads the hardware sensors
>
> s/the/multiple/
>
> > + and aggregate the temperature.
>
> "aggregates their output"
>
> > +
> > config HISI_THERMAL
> > tristate "Hisilicon thermal driver"
> > depends on ARCH_HISI || COMPILE_TEST
> > diff --git a/drivers/thermal/Makefile b/drivers/thermal/Makefile
> > index 82fc3e616e54b..8bf55973059c5 100644
> > --- a/drivers/thermal/Makefile
> > +++ b/drivers/thermal/Makefile
> > @@ -60,3 +60,4 @@ obj-$(CONFIG_UNIPHIER_THERMAL) += uniphier_thermal.o
> > obj-$(CONFIG_AMLOGIC_THERMAL) += amlogic_thermal.o
> > obj-$(CONFIG_SPRD_THERMAL) += sprd_thermal.o
> > obj-$(CONFIG_KHADAS_MCU_FAN_THERMAL) += khadas_mcu_fan.o
> > +obj-$(CONFIG_VIRTUAL_THERMAL) += virtual_thermal_sensor.o
> > diff --git a/drivers/thermal/virtual-thermal-sensor.h b/drivers/thermal/virtual-thermal-sensor.h
> > new file mode 100644
> > index 0000000000000..3bbf7c324dddc
> > --- /dev/null
> > +++ b/drivers/thermal/virtual-thermal-sensor.h
> > @@ -0,0 +1,54 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * Copyright (c) 2021 BayLibre
> > + */
> > +
> > +#ifndef __THERMAL_VIRTUAL_SENSOR_H__
> > +#define __THERMAL_VIRTUAL_SENSOR_H__
> > +
> > +#include <linux/device.h>
> > +#include <linux/thermal.h>
> > +
> > +struct virtual_thermal_sensor;
> > +struct thermal_sensor_data;
> > +
> > +#if IS_ENABLED(CONFIG_VIRTUAL_THERMAL)
> > +struct thermal_sensor_data *
> > +thermal_virtual_sensor_register(struct device *dev, int sensor_id, void *data,
> > + const struct thermal_zone_of_device_ops *ops);
> > +void thermal_virtual_sensor_unregister(struct device *dev,
> > + struct thermal_sensor_data *sensor_data);
> > +struct thermal_sensor_data *
> > +devm_thermal_virtual_sensor_register(struct device *dev, int sensor_id, void *data,
> > + const struct thermal_zone_of_device_ops *ops);
> > +
> > +void devm_thermal_virtual_sensor_unregister(struct device *dev,
> > + struct virtual_thermal_sensor *sensor);
> > +#else
> > +static inline struct thermal_sensor_data *
> > +thermal_virtual_sensor_register(struct device *dev, int sensor_id, void *data,
> > + const struct thermal_zone_of_device_ops *ops)
> > +{
> > + return ERR_PTR(-ENODEV);
> > +}
> > +
> > +void thermal_virtual_sensor_unregister(struct device *dev,
> > + struct thermal_sensor_data *sensor_data)
> > +{
> > +}
> > +
> > +static inline struct thermal_sensor_data *
> > +devm_thermal_virtual_sensor_register(struct device *dev, int sensor_id, void *data,
> > + const struct thermal_zone_of_device_ops *ops)
> > +{
> > + return ERR_PTR(-ENODEV);
> > +}
> > +
> > +static inline
> > +void devm_thermal_virtual_sensor_unregister(struct device *dev,
> > + struct virtual_thermal_sensor *sensor)
> > +{
> > +}
> > +#endif
> > +
> > +#endif /* __THERMAL_VIRTUAL_SENSOR_H__ */
> > diff --git a/drivers/thermal/virtual_thermal_sensor.c b/drivers/thermal/virtual_thermal_sensor.c
> > new file mode 100644
> > index 0000000000000..234563af6643e
> > --- /dev/null
> > +++ b/drivers/thermal/virtual_thermal_sensor.c
> > @@ -0,0 +1,350 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright (c) 2021 BayLibre
>
> Please add information on what's in this file to the preamble.
>
> > + */
> > +
> > +#include <linux/err.h>
> > +#include <linux/export.h>
> > +#include <linux/module.h>
> > +#include <linux/of_device.h>
> > +#include <linux/of_platform.h>
> > +#include <linux/slab.h>
> > +#include <linux/thermal.h>
> > +#include <linux/types.h>
> > +#include <linux/string.h>
> > +
> > +#include <dt-bindings/thermal/virtual-sensor.h>
> > +
> > +#include "virtual-thermal-sensor.h"
> > +
> > +struct thermal_sensor_data {
> > + struct list_head node;
> > +
> > + /* sensor interface */
> > + int id;
> > + void *sensor_data;
> > + const struct thermal_zone_of_device_ops *ops;
> > +};
> > +
> > +struct virtual_thermal_sensor {
> > + int count;
> > + struct thermal_sensor_data *sensors;
> > + struct thermal_zone_device *tzd;
> > + int (*aggr_temp)(int temp1, int temp2);
> > +
> > + struct list_head node;
> > +};
> > +
> > +static LIST_HEAD(thermal_sensors);
> > +static LIST_HEAD(virtual_sensors);
>
> These lists don't seem to be protected against concurrent access and
> they should be.
>
> > +
> > +static int max_temp(int temp1, int temp2)
> > +{
> > + return max(temp1, temp2);
> > +}
> > +
> > +static int min_temp(int temp1, int temp2)
> > +{
> > + return min(temp1, temp2);
> > +}
> > +
> > +static int avg_temp(int temp1, int temp2)
> > +{
> > + return ((temp1) / 2) + ((temp2) / 2) + (((temp1) % 2 + (temp2) % 2) / 2);
>
> There are a few redundant parens here.
>
> And why not
>
> return (temp1 + temp2) / 2;
>
> > +}
> > +
> > +static int virtual_thermal_sensor_get_temp(void *data, int *temperature)
> > +{
> > + struct virtual_thermal_sensor *sensor = data;
> > + int max_temp = INT_MIN;
> > + int temp;
> > + int i;
> > +
>
> Some synchronization (eg. locking) should be added to this. It is racy as is.
>
> > + for (i = 0; i < sensor->count; i++) {
> > + struct thermal_sensor_data *hw_sensor;
> > +
> > + hw_sensor = &sensor->sensors[i];
> > + if (!hw_sensor->ops)
> > + return -ENODEV;
> > +
> > + hw_sensor->ops->get_temp(hw_sensor->sensor_data, &temp);
> > + max_temp = sensor->aggr_temp(max_temp, temp);
> > + }
> > +
> > + *temperature = max_temp;
> > +
> > + return 0;
> > +}
> > +
> > +static const struct thermal_zone_of_device_ops virtual_thermal_sensor_ops = {
> > + .get_temp = virtual_thermal_sensor_get_temp,
> > +};
> > +
> > +static int virtual_sensor_add_sensor(struct virtual_thermal_sensor *sensor,
> > + struct of_phandle_args args,
> > + int index)
> > +{
> > + struct thermal_sensor_data *sensor_data;
> > + int id;
> > +
> > + list_for_each_entry(sensor_data, &thermal_sensors, node) {
> > + id = args.args_count ? args.args[0] : 0;
> > + if (sensor_data->id == id) {
> > + memcpy(&sensor->sensors[index], sensor_data,
> > + sizeof(*sensor_data));
>
> The data object being copied includes pointers, so I wouldn't copy
> them like this. Especially the ops one annotated as const.
>
> > + return 0;
> > + }
> > + }
> > +
> > + return -ENODEV;
> > +}
> > +
> > +static int virtual_thermal_sensor_probe(struct platform_device *pdev)
> > +{
> > + struct virtual_thermal_sensor *sensor;
> > + struct device *dev = &pdev->dev;
> > + struct of_phandle_args args;
> > + u32 type;
> > + int ret;
> > + int i;
> > +
> > + sensor = devm_kzalloc(dev, sizeof(*sensor), GFP_KERNEL);
> > + if (!sensor)
> > + return -ENOMEM;
> > +
> > + sensor->count = of_count_phandle_with_args(dev->of_node,
> > + "thermal-sensors",
> > + "#thermal-sensor-cells");
> > + if (sensor->count <= 0)
> > + return -EINVAL;
> > +
> > + sensor->sensors = devm_kmalloc_array(dev, sensor->count,
> > + sizeof(*sensor->sensors),
> > + GFP_KERNEL);
> > + if (!sensor->sensors)
> > + return -ENOMEM;
> > +
> > + for (i = 0; i < sensor->count; i++) {
> > + ret = of_parse_phandle_with_args(dev->of_node,
> > + "thermal-sensors",
> > + "#thermal-sensor-cells",
> > + i,
> > + &args);
> > + if (ret)
> > + return ret;
> > +
> > + ret = virtual_sensor_add_sensor(sensor, args, i);
> > + if (ret)
> > + return ret;
> > + }
> > +
> > + ret = of_property_read_u32(dev->of_node, "aggregation-function", &type);
> > + if (ret)
> > + return ret;
> > +
> > + switch (type) {
> > + case VIRTUAL_THERMAL_SENSOR_MAX:
> > + sensor->aggr_temp = max_temp;
> > + break;
> > + case VIRTUAL_THERMAL_SENSOR_MIN:
> > + sensor->aggr_temp = min_temp;
> > + break;
> > + case VIRTUAL_THERMAL_SENSOR_AVG:
> > + sensor->aggr_temp = avg_temp;
> > + break;
> > + default:
> > + return -EINVAL;
> > + }
> > +
> > + sensor->tzd = devm_thermal_zone_of_sensor_register(dev, 0, sensor,
> > + &virtual_thermal_sensor_ops);
> > + if (IS_ERR(sensor->tzd))
> > + return PTR_ERR(sensor->tzd);
> > +
> > + platform_set_drvdata(pdev, sensor);
> > + list_add(&sensor->node, &virtual_sensors);
> > +
> > + return 0;
> > +}
> > +
> > +static int virtual_thermal_sensor_remove(struct platform_device *pdev)
> > +{
> > + struct virtual_thermal_sensor *sensor;
> > +
> > + sensor = platform_get_drvdata(pdev);
> > + list_del(&sensor->node);
> > +
> > + return 0;
> > +}
> > +
> > +static const struct of_device_id virtual_thermal_sensor_of_match[] = {
> > + {
> > + .compatible = "virtual,thermal-sensor",
> > + },
> > + {
> > + },
> > +};
> > +MODULE_DEVICE_TABLE(of, virtual_thermal_sensor_of_match);
> > +
> > +static struct platform_driver virtual_thermal_sensor = {
> > + .probe = virtual_thermal_sensor_probe,
> > + .remove = virtual_thermal_sensor_remove,
> > + .driver = {
> > + .name = "virtual-thermal-sensor",
> > + .of_match_table = virtual_thermal_sensor_of_match,
> > + },
> > +};
> > +
> > +/**
> > + * thermal_virtual_sensor_register - registers a sensor that could be a virtual
> > + * sensor
> > + * @dev: a valid struct device pointer of a sensor device. Must contain
> > + * a valid .of_node, for the sensor node.
> > + * @sensor_id: a sensor identifier, in case the sensor IP has more
> > + * than one sensor
> > + * @data: a private pointer (owned by the caller) that will be passed
> > + * back, when a temperature reading is needed.
> > + * @ops: struct thermal_zone_of_device_ops *. Must contain at least .get_temp.
> > + *
> > + * This function will register a thermal sensor to make it available for later
> > + * usage by a virtual sensor.
>
> So who's expected to be calling it?
>
> > + *
> > + * The thermal zone temperature is provided by the @get_temp function
> > + * pointer. When called, it will have the private pointer @data back.
>
> It is unclear what you mean here. I think you are describing a return
> mechanism, but as is it is hard to follow.
>
> > + *
> > + * Return: On success returns a valid struct thermal_zone_device,
>
> That doesn't seem to be the case. It returns an address returned by
> devm_kzalloc() and the memory at that address is expected to be a
> thermal_sensor_data object.
>
> > + * otherwise, it returns a corresponding ERR_PTR(). Caller must
> > + * check the return value with help of IS_ERR() helper.
> > + */
> > +struct thermal_sensor_data *thermal_virtual_sensor_register(
> > + struct device *dev, int sensor_id, void *data,
> > + const struct thermal_zone_of_device_ops *ops)
> > +{
> > + struct thermal_sensor_data *sensor_data;
> > +
> > + sensor_data = devm_kzalloc(dev, sizeof(*sensor_data), GFP_KERNEL);
> > + if (!sensor_data)
> > + return ERR_PTR(-ENOMEM);
> > +
> > + sensor_data->id = sensor_id;
> > + sensor_data->sensor_data = data;
> > + sensor_data->ops = ops;
> > +
> > + list_add(&sensor_data->node, &thermal_sensors);
> > +
> > + return sensor_data;
>
> Overall, this is non-modular code squeezed into a module.
>
> If this module goes away and whoever called it wants to unregister the
> sensor, they will crash, so to a minimum it should do a
> try_module_get() on the module containing it.
And that wouldn't be sufficient either, because in theory the module
may go away before that try_module_get() gets called. Sorry for the
confusion.
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