Re: [PATCH RFC 3/6] hwmon: Add support for RPi voltage sensor

[Guenter Roeck <linux@roeck-us.net>]

On Wed, May 16, 2018 at 09:59:01PM +0200, Stefan Wahren wrote:
> Hi Guenter,
> 
> > Guenter Roeck <linux@roeck-us.net> hat am 16. Mai 2018 um 20:21 geschrieben:
> > 
> > 
> > On Wed, May 16, 2018 at 03:37:04PM +0200, Stefan Wahren wrote:
> > > Currently there is no easy way to detect under-voltage conditions on a remote
> > > Raspberry Pi. This hwmon driver retrieves the state of the under-voltage sensor
> > > via mailbox interface. The handling based on Noralf's modifications to the
> > > downstream firmware driver. In case of an under-voltage condition only an entry
> > > is written to the kernel log.
> > > 
> > 
> > My major concern is how this is displayed with the 'sensors' command.
> > Can you test and report ?
> 
> I get the following output:
> rpi_volt-isa-0000
> Adapter: ISA adapter
> in0:              N/A  
> 
Ok, that works.

> > 
> > Of course, it would be much better if the firmware would also report
> > the actual voltage, but I guess we can't have everything.
> 
> I think this isn't possible because the hardware only provide a binary value (GPIO).
> 
> > 
> > More comments inline.
> > 
> > Thanks,
> > Guenter
> > 
> > > CC: "Noralf Trønnes" <noralf@tronnes.org>
> > > Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
> > > ---
> > >  drivers/hwmon/Kconfig             |  10 ++
> > >  drivers/hwmon/Makefile            |   1 +
> > >  drivers/hwmon/raspberrypi-hwmon.c | 207 ++++++++++++++++++++++++++++++++++++++
> > 
> > Please also provide Documentation/hwmon/raspberrypi-hwmon.
> > 
> > >  3 files changed, 218 insertions(+)
> > >  create mode 100644 drivers/hwmon/raspberrypi-hwmon.c
> > > 
> > > diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
> > > index 768aed5..7f935cf 100644
> > > --- a/drivers/hwmon/Kconfig
> > > +++ b/drivers/hwmon/Kconfig
> > > @@ -1298,6 +1298,16 @@ config SENSORS_PWM_FAN
> > >  	  This driver can also be built as a module.  If so, the module
> > >  	  will be called pwm-fan.
> > >  
> > > +config SENSORS_RASPBERRYPI_HWMON
> > > +	tristate "Raspberry Pi voltage monitor"
> > > +	depends on (ARCH_BCM2835 && RASPBERRYPI_FIRMWARE) || (COMPILE_TEST && !RASPBERRYPI_FIRMWARE)
> > > +	help
> > > +	  If you say yes here you get support for voltage sensor on the
> > > +	  Raspberry Pi.
> > > +
> > > +	  This driver can also be built as a module. If so, the module
> > > +	  will be called raspberrypi-hwmon.
> > > +
> > >  config SENSORS_SHT15
> > >  	tristate "Sensiron humidity and temperature sensors. SHT15 and compat."
> > >  	depends on GPIOLIB || COMPILE_TEST
> > > diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
> > > index e7d52a3..a929770 100644
> > > --- a/drivers/hwmon/Makefile
> > > +++ b/drivers/hwmon/Makefile
> > > @@ -141,6 +141,7 @@ obj-$(CONFIG_SENSORS_PC87427)	+= pc87427.o
> > >  obj-$(CONFIG_SENSORS_PCF8591)	+= pcf8591.o
> > >  obj-$(CONFIG_SENSORS_POWR1220)  += powr1220.o
> > >  obj-$(CONFIG_SENSORS_PWM_FAN)	+= pwm-fan.o
> > > +obj-$(CONFIG_SENSORS_RASPBERRYPI_HWMON)	+= raspberrypi-hwmon.o
> > >  obj-$(CONFIG_SENSORS_S3C)	+= s3c-hwmon.o
> > >  obj-$(CONFIG_SENSORS_SCH56XX_COMMON)+= sch56xx-common.o
> > >  obj-$(CONFIG_SENSORS_SCH5627)	+= sch5627.o
> > > diff --git a/drivers/hwmon/raspberrypi-hwmon.c b/drivers/hwmon/raspberrypi-hwmon.c
> > > new file mode 100644
> > > index 0000000..2003f6c
> > > --- /dev/null
> > > +++ b/drivers/hwmon/raspberrypi-hwmon.c
> > > @@ -0,0 +1,207 @@
> > > +// SPDX-License-Identifier: GPL-2.0+
> > > +/*
> > > + * Raspberry Pi voltage sensor driver
> > > + *
> > > + * Based on firmware/raspberrypi.c by Noralf Trønnes
> > > + *
> > > + * Copyright (C) 2018 Stefan Wahren <stefan.wahren@i2se.com>
> > > + */
> > > +#include <linux/device.h>
> > > +#include <linux/err.h>
> > > +#include <linux/hwmon.h>
> > > +#include <linux/hwmon-sysfs.h>
> > 
> > Unnecessary include
> > 
> > > +#include <linux/module.h>
> > > +#include <linux/of_device.h>
> > > +#include <linux/platform_device.h>
> > > +#include <linux/slab.h>
> > > +#include <linux/workqueue.h>
> > > +#include <soc/bcm2835/raspberrypi-firmware.h>
> > > +
> > > +#define UNDERVOLTAGE_STICKY_BIT	BIT(16)
> > > +
> > > +struct rpi_hwmon_data {
> > > +	struct device *hwmon_dev;
> > > +	struct rpi_firmware *fw;
> > > +	u32 last_throttled;
> > > +	struct delayed_work get_values_poll_work;
> > > +};
> > > +
> > > +static void rpi_firmware_get_throttled(struct rpi_hwmon_data *data)
> > > +{
> > > +	u32 new_uv, old_uv, value;
> > > +	int ret;
> > > +
> > > +	/* Clear sticky bits */
> > 
> > Please make more explicit that this is a request/command sent to the firmware.
> > 
> > > +	value = 0xffff;
> > > +
> > > +	ret = rpi_firmware_property(data->fw, RPI_FIRMWARE_GET_THROTTLED,
> > > +				    &value, sizeof(value));
> > > +	if (ret) {
> > > +		dev_err_once(data->hwmon_dev, "%s: Failed to get throttled (%d)\n",
> > > +			     __func__, ret);
> > 
> > The function name seems unnecessary.
> > 
> > > +		return;
> > > +	}
> > > +
> > > +	new_uv = value & UNDERVOLTAGE_STICKY_BIT;
> > > +	old_uv = data->last_throttled & UNDERVOLTAGE_STICKY_BIT;
> > > +	data->last_throttled = value;
> > > +
> > > +	if (new_uv == old_uv)
> > > +		return;
> > > +
> > > +	if (new_uv)
> > > +		dev_crit(data->hwmon_dev, "Under-voltage detected! (0x%08x)\n",
> > > +			 value);
> > > +	else
> > > +		dev_info(data->hwmon_dev, "Voltage normalised (0x%08x)\n",
> > > +			 value);
> > 
> > What value do those hex values provide to the user ?
> 
> The actual definition of the bits can be found in the commit log of patch #1. But this isn't very helpful for an end user.
> 
I would suggest to drop the value from the log.

> > 
> > > +
> > > +	sysfs_notify(&data->hwmon_dev->kobj, NULL, "in0_lcrit_alarm");
> > > +}
> > > +
> > > +static void get_values_poll(struct work_struct *work)
> > > +{
> > > +	struct rpi_hwmon_data *data;
> > > +
> > > +	data = container_of(work, struct rpi_hwmon_data,
> > > +			    get_values_poll_work.work);
> > > +
> > > +	rpi_firmware_get_throttled(data);
> > > +
> > > +	/*
> > > +	 * We can't run faster than the sticky shift (100ms) since we get
> > > +	 * flipping in the sticky bits that are cleared.
> > > +	 */
> > > +	schedule_delayed_work(&data->get_values_poll_work, 2 * HZ);
> > > +}
> > > +
> > > +static int rpi_read(struct device *dev, enum hwmon_sensor_types type,
> > > +		    u32 attr, int channel, long *val)
> > > +{
> > > +	struct rpi_hwmon_data *data = dev_get_drvdata(dev);
> > > +
> > > +	if (type != hwmon_in)
> > > +		return -EOPNOTSUPP;
> > > +
> > > +	if (attr != hwmon_in_lcrit_alarm)
> > > +		return -EOPNOTSUPP;
> > > +
> > > +	if (channel)
> > > +		return -EOPNOTSUPP;
> > > +
> > There is only one channel, one attribute, and one type supported.
> > As such, the checks are unnecessary.
> > 
> > > +	*val = !!(data->last_throttled & UNDERVOLTAGE_STICKY_BIT);
> > > +	return 0;
> > > +}
> > > +
> > > +static umode_t rpi_is_visible(const void *_data, enum hwmon_sensor_types type,
> > > +			      u32 attr, int channel)
> > > +{
> > > +	if (type != hwmon_in)
> > > +		return 0;
> > > +
> > > +	if (attr != hwmon_in_lcrit_alarm)
> > > +		return 0;
> > > +
> > > +	if (channel)
> > > +		return 0;
> > 
> > Same as above. In the list below, there is not a single conditional attribute.
> > Given that, the checks should be unnecessary, and it should be sufficient to
> > just return 0444.
> > 
> > > +
> > > +	return 0444;
> > > +}
> > > +
> > > +static const u32 rpi_in_config[] = {
> > > +	HWMON_I_LCRIT_ALARM,
> > > +	0
> > > +};
> > > +
> > > +static const struct hwmon_channel_info rpi_in = {
> > > +	.type = hwmon_in,
> > > +	.config = rpi_in_config,
> > > +};
> > > +
> > > +static const struct hwmon_channel_info *rpi_info[] = {
> > > +	&rpi_in,
> > > +	NULL
> > > +};
> > > +
> > > +static const struct hwmon_ops rpi_hwmon_ops = {
> > > +	.is_visible = rpi_is_visible,
> > > +	.read = rpi_read,
> > > +};
> > > +
> > > +static const struct hwmon_chip_info rpi_chip_info = {
> > > +	.ops = &rpi_hwmon_ops,
> > > +	.info = rpi_info,
> > > +};
> > > +
> > > +static int rpi_hwmon_probe(struct platform_device *pdev)
> > > +{
> > > +	struct device *dev = &pdev->dev;
> > > +	struct device_node *fw_node;
> > > +	struct rpi_hwmon_data *data;
> > > +	int ret;
> > > +
> > > +	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
> > > +	if (!data)
> > > +		return -ENOMEM;
> > > +
> > > +	fw_node = of_get_parent(dev->of_node);
> > > +	if (!fw_node) {
> > > +		dev_err(dev, "Missing firmware node\n");
> > > +		return -ENOENT;
> > > +	}
> > > +
> > > +	data->fw = rpi_firmware_get(fw_node);
> > > +	of_node_put(fw_node);
> > > +	if (!data->fw)
> > > +		return -EPROBE_DEFER;
> > > +
> > > +	ret = rpi_firmware_property(data->fw, RPI_FIRMWARE_GET_THROTTLED,
> > > +				    &data->last_throttled,
> > > +				    sizeof(data->last_throttled));
> > > +	if (ret) {
> > > +		dev_info(dev, "Firmware doesn't support GET_THROTTLED\n");
> > 
> > If this is an error -> dev_err().
> 
> I wasn't sure. If the firmware is too old, we cannot provide this feature and it's a waste of resources to load this driver. On the other side i don't want to confuse people this is something bad.
> 
Then I would suggest to return -ENODEV.

Guenter

> Stefan
> 
> > 
> > > +		return -EOPNOTSUPP;
> > 
> > or return -ENODEV.
> > 
> > > +	}
> > > +
> > > +	data->hwmon_dev = devm_hwmon_device_register_with_info(dev, "rpi_volt",
> > > +							       data,
> > > +							       &rpi_chip_info,
> > > +							       NULL);
> > > +
> > > +	INIT_DELAYED_WORK(&data->get_values_poll_work, get_values_poll);
> > > +	platform_set_drvdata(pdev, data);
> > > +
> > > +	if (!PTR_ERR_OR_ZERO(data->hwmon_dev))
> > > +		schedule_delayed_work(&data->get_values_poll_work, 2 * HZ);
> > > +
> > > +	return PTR_ERR_OR_ZERO(data->hwmon_dev);
> > > +}
> > > +
> > > +static int rpi_hwmon_remove(struct platform_device *pdev)
> > > +{
> > > +	struct rpi_hwmon_data *data = platform_get_drvdata(pdev);
> > > +
> > > +	cancel_delayed_work_sync(&data->get_values_poll_work);
> > > +
> > > +	return 0;
> > > +}
> > > +
> > > +static const struct of_device_id rpi_hwmon_of_match[] = {
> > > +	{ .compatible = "raspberrypi,bcm2835-hwmon", },
> > > +	{ /* sentinel */},
> > > +};
> > > +MODULE_DEVICE_TABLE(of, rpi_hwmon_of_match);
> > > +
> > > +static struct platform_driver rpi_hwmon_driver = {
> > > +	.probe = rpi_hwmon_probe,
> > > +	.remove = rpi_hwmon_remove,
> > > +	.driver = {
> > > +		.name = "raspberrypi-hwmon",
> > > +		.of_match_table = rpi_hwmon_of_match,
> > > +	},
> > > +};
> > > +module_platform_driver(rpi_hwmon_driver);
> > > +
> > > +MODULE_AUTHOR("Stefan Wahren <stefan.wahren@i2se.com>");
> > > +MODULE_DESCRIPTION("Raspberry Pi voltage sensor driver");
> > > +MODULE_LICENSE("GPL v2");
> > > -- 
> > > 2.7.4
> > > 
> > > --
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