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Gerhard Engledergroeck
Gerhard Engleder
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groeck
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hwmon: Add KEBA battery monitoring controller support
The KEBA battery monitoring controller is found in the system FPGA of KEBA PLC devices. It puts a load on the coin cell battery to check the state of the battery. If the coin cell battery is nearly empty, then the user space is signaled with a hwmon alarm. The auxiliary device for this driver is instantiated by the cp500 misc driver. Signed-off-by: Gerhard Engleder <[email protected]> Link: https://lore.kernel.org/r/[email protected] Signed-off-by: Guenter Roeck <[email protected]>
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‎Documentation/hwmon/index.rst

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@@ -106,6 +106,7 @@ Hardware Monitoring Kernel Drivers
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jc42
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k10temp
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k8temp
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kbatt
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lan966x
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lineage-pem
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lm25066

‎Documentation/hwmon/kbatt.rst

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.. SPDX-License-Identifier: GPL-2.0
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Kernel driver kbatt
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===================
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Supported chips:
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* KEBA battery monitoring controller (IP core in FPGA)
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Prefix: 'kbatt'
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Authors:
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Gerhard Engleder <[email protected]>
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Petar Bojanic <[email protected]>
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Description
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-----------
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The KEBA battery monitoring controller is an IP core for FPGAs, which
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monitors the health of a coin cell battery. The coin cell battery is
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typically used to supply the RTC during power off to keep the current
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time. E.g., the CP500 FPGA includes this IP core to monitor the coin cell
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battery of PLCs and the corresponding cp500 driver creates an auxiliary
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device for the kbatt driver.
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This driver provides information about the coin cell battery health to
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user space. Actually the user space shall be informed that the coin cell
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battery is nearly empty and needs to be replaced.
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The coin cell battery must be tested actively to get to know if its nearly
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empty or not. Therefore, a load is put on the coin cell battery and the
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resulting voltage is evaluated. This evaluation is done by some hard wired
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analog logic, which compares the voltage to a defined limit. If the
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voltage is above the limit, then the coin cell battery is assumed to be
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ok. If the voltage is below the limit, then the coin cell battery is
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nearly empty (or broken, removed, ...) and shall be replaced by a new one.
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The KEBA battery monitoring controller allows to start the test of the
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coin cell battery and to get the result if the voltage is above or below
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the limit. The actual voltage is not available. Only the information if
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the voltage is below a limit is available.
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The test load, which is put on the coin cell battery for the health check,
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is similar to the load during power off. Therefore, the lifetime of the
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coin cell battery is reduced directly by the duration of each test. To
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limit the negative impact to the lifetime the test is limited to at most
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once every 10 seconds. The test load is put on the coin cell battery for
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100ms. Thus, in worst case the coin cell battery lifetime is reduced by
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1% of the uptime or 3.65 days per year. As the coin cell battery lasts
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multiple years, this lifetime reduction negligible.
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This driver only provides a single alarm attribute, which is raised when
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the coin cell battery is nearly empty.
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====================== ==== ===================================================
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Attribute R/W Contents
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====================== ==== ===================================================
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in0_min_alarm R voltage of coin cell battery under load is below
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limit
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====================== ==== ===================================================

‎drivers/hwmon/Kconfig

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This driver can also be built as a module. If so, the module
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will be called k10temp.
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config SENSORS_KBATT
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tristate "KEBA battery controller support"
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depends on KEBA_CP500
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help
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This driver supports the battery monitoring controller found in
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KEBA system FPGA devices.
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This driver can also be built as a module. If so, the module
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will be called kbatt.
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config SENSORS_FAM15H_POWER
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tristate "AMD Family 15h processor power"
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depends on X86 && PCI && CPU_SUP_AMD

‎drivers/hwmon/Makefile

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obj-$(CONFIG_SENSORS_JC42) += jc42.o
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obj-$(CONFIG_SENSORS_K8TEMP) += k8temp.o
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obj-$(CONFIG_SENSORS_K10TEMP) += k10temp.o
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obj-$(CONFIG_SENSORS_KBATT) += kbatt.o
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obj-$(CONFIG_SENSORS_LAN966X) += lan966x-hwmon.o
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obj-$(CONFIG_SENSORS_LENOVO_EC) += lenovo-ec-sensors.o
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obj-$(CONFIG_SENSORS_LINEAGE) += lineage-pem.o

‎drivers/hwmon/kbatt.c

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// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright (C) 2025 KEBA Industrial Automation GmbH
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*
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* Driver for KEBA battery monitoring controller FPGA IP core
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*/
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#include <linux/hwmon.h>
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#include <linux/io.h>
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#include <linux/delay.h>
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#include <linux/module.h>
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#include <linux/device.h>
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#include <linux/auxiliary_bus.h>
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#include <linux/misc/keba.h>
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#include <linux/mutex.h>
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#define KBATT "kbatt"
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#define KBATT_CONTROL_REG 0x4
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#define KBATT_CONTROL_BAT_TEST 0x01
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#define KBATT_STATUS_REG 0x8
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#define KBATT_STATUS_BAT_OK 0x01
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#define KBATT_MAX_UPD_INTERVAL (10 * HZ)
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#define KBATT_SETTLE_TIME_US (100 * USEC_PER_MSEC)
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struct kbatt {
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/* update lock */
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struct mutex lock;
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void __iomem *base;
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unsigned long next_update; /* in jiffies */
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bool alarm;
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};
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static bool kbatt_alarm(struct kbatt *kbatt)
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{
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mutex_lock(&kbatt->lock);
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if (!kbatt->next_update || time_after(jiffies, kbatt->next_update)) {
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/* switch load on */
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iowrite8(KBATT_CONTROL_BAT_TEST,
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kbatt->base + KBATT_CONTROL_REG);
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/* wait some time to let things settle */
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fsleep(KBATT_SETTLE_TIME_US);
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/* check battery state */
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if (ioread8(kbatt->base + KBATT_STATUS_REG) &
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KBATT_STATUS_BAT_OK)
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kbatt->alarm = false;
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else
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kbatt->alarm = true;
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/* switch load off */
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iowrite8(0, kbatt->base + KBATT_CONTROL_REG);
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kbatt->next_update = jiffies + KBATT_MAX_UPD_INTERVAL;
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}
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mutex_unlock(&kbatt->lock);
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return kbatt->alarm;
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}
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static int kbatt_read(struct device *dev, enum hwmon_sensor_types type,
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u32 attr, int channel, long *val)
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{
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struct kbatt *kbatt = dev_get_drvdata(dev);
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*val = kbatt_alarm(kbatt) ? 1 : 0;
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return 0;
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}
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static umode_t kbatt_is_visible(const void *data, enum hwmon_sensor_types type,
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u32 attr, int channel)
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{
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if (channel == 0 && attr == hwmon_in_min_alarm)
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return 0444;
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return 0;
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}
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static const struct hwmon_channel_info *kbatt_info[] = {
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HWMON_CHANNEL_INFO(in,
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/* 0: input minimum alarm channel */
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HWMON_I_MIN_ALARM),
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NULL
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};
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static const struct hwmon_ops kbatt_hwmon_ops = {
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.is_visible = kbatt_is_visible,
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.read = kbatt_read,
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};
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static const struct hwmon_chip_info kbatt_chip_info = {
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.ops = &kbatt_hwmon_ops,
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.info = kbatt_info,
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};
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static int kbatt_probe(struct auxiliary_device *auxdev,
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const struct auxiliary_device_id *id)
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{
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struct keba_batt_auxdev *kbatt_auxdev =
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container_of(auxdev, struct keba_batt_auxdev, auxdev);
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struct device *dev = &auxdev->dev;
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struct device *hwmon_dev;
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struct kbatt *kbatt;
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int retval;
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kbatt = devm_kzalloc(dev, sizeof(*kbatt), GFP_KERNEL);
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if (!kbatt)
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return -ENOMEM;
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retval = devm_mutex_init(dev, &kbatt->lock);
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if (retval)
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return retval;
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kbatt->base = devm_ioremap_resource(dev, &kbatt_auxdev->io);
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if (IS_ERR(kbatt->base))
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return PTR_ERR(kbatt->base);
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hwmon_dev = devm_hwmon_device_register_with_info(dev, KBATT, kbatt,
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&kbatt_chip_info,
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NULL);
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return PTR_ERR_OR_ZERO(hwmon_dev);
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}
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static const struct auxiliary_device_id kbatt_devtype_aux[] = {
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{ .name = "keba.batt" },
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{}
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};
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MODULE_DEVICE_TABLE(auxiliary, kbatt_devtype_aux);
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static struct auxiliary_driver kbatt_driver_aux = {
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.name = KBATT,
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.id_table = kbatt_devtype_aux,
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.probe = kbatt_probe,
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};
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module_auxiliary_driver(kbatt_driver_aux);
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MODULE_AUTHOR("Petar Bojanic <[email protected]>");
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MODULE_AUTHOR("Gerhard Engleder <[email protected]>");
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MODULE_DESCRIPTION("KEBA battery monitoring controller driver");
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MODULE_LICENSE("GPL");

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