From 76aa41c17befa67b8727942d134eb65af501908b Mon Sep 17 00:00:00 2001 From: Andrea Merello Date: Wed, 20 Nov 2019 15:47:48 +0100 Subject: [PATCH] iio: max31856: add option for setting mains filter rejection frequency This sensor has an embedded notch filter for reducing interferences caused by the power mains. This filter can be tuned to reject either 50Hz or 60Hz (and harmonics). Currently the said setting is left alone (the sensor defaults to 60Hz). This patch introduces a IIO attribute that allows the user to set the said filter to the desired frequency. NOTE: this has been intentionally not tied to any DT property to allow the configuration of this setting from userspace, e.g. with a GUI or by reading a configuration file, or maybe reading a GPIO tied to a physical switch or accessing some device that can autodetect the line frequency. Cc: Hartmut Knaack Cc: Lars-Peter Clausen Cc: Peter Meerwald-Stadler Cc: Colin Ian King Cc: Patrick Havelange Cc: Matt Weber Cc: Matt Ranostay Cc: Chuhong Yuan Cc: Daniel Gomez Cc: linux-iio@vger.kernel.org Signed-off-by: Andrea Merello Reviewed-by: Matt Ranostay Signed-off-by: Jonathan Cameron --- drivers/iio/temperature/max31856.c | 50 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 50 insertions(+) diff --git a/drivers/iio/temperature/max31856.c b/drivers/iio/temperature/max31856.c index 73ed550..d97ba9e 100644 --- a/drivers/iio/temperature/max31856.c +++ b/drivers/iio/temperature/max31856.c @@ -23,6 +23,7 @@ #define MAX31856_CR0_1SHOT BIT(6) #define MAX31856_CR0_OCFAULT BIT(4) #define MAX31856_CR0_OCFAULT_MASK GENMASK(5, 4) +#define MAX31856_CR0_FILTER_50HZ BIT(0) #define MAX31856_TC_TYPE_MASK GENMASK(3, 0) #define MAX31856_FAULT_OVUV BIT(1) #define MAX31856_FAULT_OPEN BIT(0) @@ -63,6 +64,7 @@ static const struct iio_chan_spec max31856_channels[] = { struct max31856_data { struct spi_device *spi; u32 thermocouple_type; + bool filter_50hz; }; static int max31856_read(struct max31856_data *data, u8 reg, @@ -123,6 +125,11 @@ static int max31856_init(struct max31856_data *data) reg_cr0_val &= ~MAX31856_CR0_1SHOT; reg_cr0_val |= MAX31856_CR0_AUTOCONVERT; + if (data->filter_50hz) + reg_cr0_val |= MAX31856_CR0_FILTER_50HZ; + else + reg_cr0_val &= ~MAX31856_CR0_FILTER_50HZ; + return max31856_write(data, MAX31856_CR0_REG, reg_cr0_val); } @@ -249,12 +256,54 @@ static ssize_t show_fault_oc(struct device *dev, return show_fault(dev, MAX31856_FAULT_OPEN, buf); } +static ssize_t show_filter(struct device *dev, + struct device_attribute *attr, + char *buf) +{ + struct iio_dev *indio_dev = dev_to_iio_dev(dev); + struct max31856_data *data = iio_priv(indio_dev); + + return sprintf(buf, "%d\n", data->filter_50hz ? 50 : 60); +} + +static ssize_t set_filter(struct device *dev, + struct device_attribute *attr, + const char *buf, + size_t len) +{ + struct iio_dev *indio_dev = dev_to_iio_dev(dev); + struct max31856_data *data = iio_priv(indio_dev); + unsigned int freq; + int ret; + + ret = kstrtouint(buf, 10, &freq); + if (ret) + return ret; + + switch (freq) { + case 50: + data->filter_50hz = true; + break; + case 60: + data->filter_50hz = false; + break; + default: + return -EINVAL; + } + + max31856_init(data); + return len; +} + static IIO_DEVICE_ATTR(fault_ovuv, 0444, show_fault_ovuv, NULL, 0); static IIO_DEVICE_ATTR(fault_oc, 0444, show_fault_oc, NULL, 0); +static IIO_DEVICE_ATTR(in_temp_filter_notch_center_frequency, 0644, + show_filter, set_filter, 0); static struct attribute *max31856_attributes[] = { &iio_dev_attr_fault_ovuv.dev_attr.attr, &iio_dev_attr_fault_oc.dev_attr.attr, + &iio_dev_attr_in_temp_filter_notch_center_frequency.dev_attr.attr, NULL, }; @@ -280,6 +329,7 @@ static int max31856_probe(struct spi_device *spi) data = iio_priv(indio_dev); data->spi = spi; + data->filter_50hz = false; spi_set_drvdata(spi, indio_dev); -- 2.7.4