[PATCH v4 8/8] iio: envelope-detector: ADC driver based on a DAC and a comparator

Peter Rosin
2016-11-08T12:34:59Z

The DAC is used to find the peak level of an alternating voltage input
signal by a binary search using the output of a comparator wired to
an interrupt pin. Like so:
_
| \
input +------>-------|+ \
| \
.-------. | }---.
| | | / |
| dac|-->--|- / |
| | |_/ |
| | |
| | |
| irq|------<-------'
| |
'-------'

Signed-off-by: Peter Rosin <peda@axentia.se>
---
.../testing/sysfs-bus-iio-adc-envelope-detector | 36 ++
MAINTAINERS | 2 +
drivers/iio/adc/Kconfig | 10 +
drivers/iio/adc/Makefile | 1 +
drivers/iio/adc/envelope-detector.c | 422 +++++++++++++++++++++
5 files changed, 471 insertions(+)
create mode 100644 Documentation/ABI/testing/sysfs-bus-iio-adc-envelope-detector
create mode 100644 drivers/iio/adc/envelope-detector.c

diff --git a/Documentation/ABI/testing/sysfs-bus-iio-adc-envelope-detector b/Documentation/ABI/testing/sysfs-bus-iio-adc-envelope-detector
new file mode 100644
index 000000000000..2071f9bcfaa5
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-bus-iio-adc-envelope-detector
@@ -0,0 +1,36 @@
+What: /sys/bus/iio/devices/iio:deviceX/in_altvoltageY_invert
+Date: October 2016
+KernelVersion: 4.9
+Contact: Peter Rosin <peda@axentia.se>
+Description:
+ The DAC is used to find the peak level of an alternating
+ voltage input signal by a binary search using the output
+ of a comparator wired to an interrupt pin. Like so:
+ _
+ | \
+ input +------>-------|+ \
+ | \
+ .-------. | }---.
+ | | | / |
+ | dac|-->--|- / |
+ | | |_/ |
+ | | |
+ | | |
+ | irq|------<-------'
+ | |
+ '-------'
+ The boolean invert attribute (0/1) should be set when the
+ input signal is centered around the maximum value of the
+ dac instead of zero. The envelope detector will search
+ from below in this case and will also invert the result.
+ The edge/level of the interrupt is also switched to its
+ opposite value.
+
+What: /sys/bus/iio/devices/iio:deviceX/in_altvoltageY_compare_interval
+Date: October 2016
+KernelVersion: 4.9
+Contact: Peter Rosin <peda@axentia.se>
+Description:
+ Number of milliseconds to wait for the comparator in each
+ step of the binary search for the input peak level. Needs
+ to relate to the frequency of the input signal.
diff --git a/MAINTAINERS b/MAINTAINERS
index 0e13066ca3a2..539b20baf791 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -6136,7 +6136,9 @@ IIO ENVELOPE DETECTOR
M: Peter Rosin <peda@axentia.se>
L: linux-iio@vger.kernel.org
S: Maintained
+F: Documentation/ABI/testing/sysfs-bus-iio-adc-envelope-detector
F: Documentation/devicetree/bindings/iio/adc/envelope-detector.txt
+F: drivers/iio/adc/envelope-detector.c

IIO SUBSYSTEM AND DRIVERS
M: Jonathan Cameron <jic23@kernel.org>
diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
index 99c051490eff..de4030894f23 100644
--- a/drivers/iio/adc/Kconfig
+++ b/drivers/iio/adc/Kconfig
@@ -195,6 +195,16 @@ config DA9150_GPADC
To compile this driver as a module, choose M here: the module will be
called berlin2-adc.

+config ENVELOPE_DETECTOR
+ tristate "Envelope detector using a DAC and a comparator"
+ depends on OF
+ help
+ Say yes here to build support for an envelope detector using a DAC
+ and a comparator.
+
+ To compile this driver as a module, choose M here: the module will be
+ called envelope-detector.
+
config EXYNOS_ADC
tristate "Exynos ADC driver support"
depends on ARCH_EXYNOS || ARCH_S3C24XX || ARCH_S3C64XX || (OF && COMPILE_TEST)
diff --git a/drivers/iio/adc/Makefile b/drivers/iio/adc/Makefile
index 7a40c04c311f..0d773c6a0578 100644
--- a/drivers/iio/adc/Makefile
+++ b/drivers/iio/adc/Makefile
@@ -20,6 +20,7 @@ obj-$(CONFIG_BCM_IPROC_ADC) += bcm_iproc_adc.o
obj-$(CONFIG_BERLIN2_ADC) += berlin2-adc.o
obj-$(CONFIG_CC10001_ADC) += cc10001_adc.o
obj-$(CONFIG_DA9150_GPADC) += da9150-gpadc.o
+obj-$(CONFIG_ENVELOPE_DETECTOR) += envelope-detector.o
obj-$(CONFIG_EXYNOS_ADC) += exynos_adc.o
obj-$(CONFIG_FSL_MX25_ADC) += fsl-imx25-gcq.o
obj-$(CONFIG_HI8435) += hi8435.o
diff --git a/drivers/iio/adc/envelope-detector.c b/drivers/iio/adc/envelope-detector.c
new file mode 100644
index 000000000000..fef15c0d7c9c
--- /dev/null
+++ b/drivers/iio/adc/envelope-detector.c
@@ -0,0 +1,422 @@
+/*
+ * Driver for an envelope detector using a DAC and a comparator
+ *
+ * Copyright (C) 2016 Axentia Technologies AB
+ *
+ * Author: Peter Rosin <peda@axentia.se>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+/*
+ * The DAC is used to find the peak level of an alternating voltage input
+ * signal by a binary search using the output of a comparator wired to
+ * an interrupt pin. Like so:
+ * _
+ * | \
+ * input +------>-------|+ \
+ * | \
+ * .-------. | }---.
+ * | | | / |
+ * | dac|-->--|- / |
+ * | | |_/ |
+ * | | |
+ * | | |
+ * | irq|------<-------'
+ * | |
+ * '-------'
+ */
+
+#include <linux/completion.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/iio/consumer.h>
+#include <linux/iio/iio.h>
+#include <linux/iio/sysfs.h>
+#include <linux/interrupt.h>
+#include <linux/irq.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
+#include <linux/platform_device.h>
+#include <linux/spinlock.h>
+#include <linux/workqueue.h>
+
+struct envelope {
+ spinlock_t comp_lock; /* protects comp */
+ int comp;
+
+ struct mutex read_lock; /* protects everything else */
+
+ int comp_irq;
+ u32 comp_irq_trigger;
+ u32 comp_irq_trigger_inv;
+
+ struct iio_channel *dac;
+ struct delayed_work comp_timeout;
+
+ unsigned int comp_interval;
+ bool invert;
+ u32 dac_max;
+
+ int high;
+ int level;
+ int low;
+
+ struct completion done;
+};
+
+/*
+ * The envelope_detector_comp_latch function works together with the compare
+ * interrupt service routine below (envelope_detector_comp_isr) as a latch
+ * (one-bit memory) for if the interrupt has triggered since last calling
+ * this function.
+ * The ..._comp_isr function disables the interrupt so that the cpu does not
+ * need to service a possible interrupt flood from the comparator when no-one
+ * cares anyway, and this ..._comp_latch function reenables them again if
+ * needed.
+ */
+static int envelope_detector_comp_latch(struct envelope *env)
+{
+ int comp;
+
+ spin_lock_irq(&env->comp_lock);
+ comp = env->comp;
+ env->comp = 0;
+ spin_unlock_irq(&env->comp_lock);
+
+ if (!comp)
+ return 0;
+
+ /*
+ * The irq was disabled, and is reenabled just now.
+ * But there might have been a pending irq that
+ * happened while the irq was disabled that fires
+ * just as the irq is reenabled. That is not what
+ * is desired.
+ */
+ enable_irq(env->comp_irq);
+
+ /* So, synchronize this possibly pending irq... */
+ synchronize_irq(env->comp_irq);
+
+ /* ...and redo the whole dance. */
+ spin_lock_irq(&env->comp_lock);
+ comp = env->comp;
+ env->comp = 0;
+ spin_unlock_irq(&env->comp_lock);
+
+ if (comp)
+ enable_irq(env->comp_irq);
+
+ return 1;
+}
+
+static irqreturn_t envelope_detector_comp_isr(int irq, void *ctx)
+{
+ struct envelope *env = ctx;
+
+ spin_lock(&env->comp_lock);
+ env->comp = 1;
+ disable_irq_nosync(env->comp_irq);
+ spin_unlock(&env->comp_lock);
+
+ return IRQ_HANDLED;
+}
+
+static void envelope_detector_setup_compare(struct envelope *env)
+{
+ int ret;
+
+ /*
+ * Do a binary search for the peak input level, and stop
+ * when that level is "trapped" between two adjacent DAC
+ * values.
+ * When invert is active, use the midpoint floor so that
+ * env->level ends up as env->low when the termination
+ * criteria below is fulfilled, and use the midpoint
+ * ceiling when invert is not active so that env->level
+ * ends up as env->high in that case.
+ */
+ env->level = (env->high + env->low + !env->invert) / 2;
+
+ if (env->high == env->low + 1) {
+ complete(&env->done);
+ return;
+ }
+
+ /* Set a "safe" DAC level (if there is such a thing)... */
+ ret = iio_write_channel_raw(env->dac, env->invert ? 0 : env->dac_max);
+ if (ret < 0)
+ goto err;
+
+ /* ...clear the comparison result... */
+ envelope_detector_comp_latch(env);
+
+ /* ...set the real DAC level... */
+ ret = iio_write_channel_raw(env->dac, env->level);
+ if (ret < 0)
+ goto err;
+
+ /* ...and wait for a bit to see if the latch catches anything. */
+ schedule_delayed_work(&env->comp_timeout,
+ msecs_to_jiffies(env->comp_interval));
+ return;
+
+err:
+ env->level = ret;
+ complete(&env->done);
+}
+
+static void envelope_detector_timeout(struct work_struct *work)
+{
+ struct envelope *env = container_of(work, struct envelope,
+ comp_timeout.work);
+
+ /* Adjust low/high depending on the latch content... */
+ if (!envelope_detector_comp_latch(env) ^ !env->invert)
+ env->low = env->level;
+ else
+ env->high = env->level;
+
+ /* ...and continue the search. */
+ envelope_detector_setup_compare(env);
+}
+
+static int envelope_detector_read_raw(struct iio_dev *indio_dev,
+ struct iio_chan_spec const *chan,
+ int *val, int *val2, long mask)
+{
+ struct envelope *env = iio_priv(indio_dev);
+ int ret;
+
+ switch (mask) {
+ case IIO_CHAN_INFO_RAW:
+ /*
+ * When invert is active, start with high=max+1 and low=0
+ * since we will end up with the low value when the
+ * termination criteria is fulfilled (rounding down). And
+ * start with high=max and low=-1 when invert is not active
+ * since we will end up with the high value in that case.
+ * This ensures that the returned value in both cases are
+ * in the same range as the DAC and is a value that has not
+ * triggered the comparator.
+ */
+ mutex_lock(&env->read_lock);
+ env->high = env->dac_max + env->invert;
+ env->low = -1 + env->invert;
+ envelope_detector_setup_compare(env);
+ wait_for_completion(&env->done);
+ if (env->level < 0) {
+ ret = env->level;
+ goto err_unlock;
+ }
+ *val = env->invert ? env->dac_max - env->level : env->level;
+ mutex_unlock(&env->read_lock);
+
+ return IIO_VAL_INT;
+
+ case IIO_CHAN_INFO_SCALE:
+ return iio_read_channel_scale(env->dac, val, val2);
+ }
+
+ return -EINVAL;
+
+err_unlock:
+ mutex_unlock(&env->read_lock);
+ return ret;
+}
+
+static ssize_t envelope_show_invert(struct iio_dev *indio_dev,
+ uintptr_t private,
+ struct iio_chan_spec const *ch, char *buf)
+{
+ struct envelope *env = iio_priv(indio_dev);
+
+ return sprintf(buf, "%u\n", env->invert);
+}
+
+static ssize_t envelope_store_invert(struct iio_dev *indio_dev,
+ uintptr_t private,
+ struct iio_chan_spec const *ch,
+ const char *buf, size_t len)
+{
+ struct envelope *env = iio_priv(indio_dev);
+ unsigned long invert;
+ int ret;
+ u32 trigger;
+
+ ret = kstrtoul(buf, 0, &invert);
+ if (ret < 0)
+ return ret;
+ if (invert > 1)
+ return -EINVAL;
+
+ trigger = invert ? env->comp_irq_trigger_inv : env->comp_irq_trigger;
+
+ mutex_lock(&env->read_lock);
+ if (invert != env->invert)
+ ret = irq_set_irq_type(env->comp_irq, trigger);
+ if (!ret) {
+ env->invert = invert;
+ ret = len;
+ }
+ mutex_unlock(&env->read_lock);
+
+ return ret;
+}
+
+static ssize_t envelope_show_comp_interval(struct iio_dev *indio_dev,
+ uintptr_t private,
+ struct iio_chan_spec const *ch,
+ char *buf)
+{
+ struct envelope *env = iio_priv(indio_dev);
+
+ return sprintf(buf, "%u\n", env->comp_interval);
+}
+
+static ssize_t envelope_store_comp_interval(struct iio_dev *indio_dev,
+ uintptr_t private,
+ struct iio_chan_spec const *ch,
+ const char *buf, size_t len)
+{
+ struct envelope *env = iio_priv(indio_dev);
+ unsigned long interval;
+ int ret;
+
+ ret = kstrtoul(buf, 0, &interval);
+ if (ret < 0)
+ return ret;
+ if (interval > 1000)
+ return -EINVAL;
+
+ mutex_lock(&env->read_lock);
+ env->comp_interval = interval;
+ mutex_unlock(&env->read_lock);
+
+ return len;
+}
+
+static const struct iio_chan_spec_ext_info envelope_detector_ext_info[] = {
+ { .name = "invert",
+ .read = envelope_show_invert,
+ .write = envelope_store_invert, },
+ { .name = "compare_interval",
+ .read = envelope_show_comp_interval,
+ .write = envelope_store_comp_interval, },
+ { /* sentinel */ }
+};
+
+static const struct iio_chan_spec envelope_detector_iio_channel = {
+ .type = IIO_ALTVOLTAGE,
+ .info_mask_separate = BIT(IIO_CHAN_INFO_RAW)
+ | BIT(IIO_CHAN_INFO_SCALE),
+ .ext_info = envelope_detector_ext_info,
+ .indexed = 1,
+};
+
+static const struct iio_info envelope_detector_info = {
+ .read_raw = &envelope_detector_read_raw,
+ .driver_module = THIS_MODULE,
+};
+
+static int envelope_detector_probe(struct platform_device *pdev)
+{
+ struct device *dev = &pdev->dev;
+ struct iio_dev *indio_dev;
+ struct envelope *env;
+ enum iio_chan_type type;
+ int ret;
+
+ indio_dev = devm_iio_device_alloc(dev, sizeof(*env));
+ if (!indio_dev)
+ return -ENOMEM;
+
+ platform_set_drvdata(pdev, indio_dev);
+ env = iio_priv(indio_dev);
+ env->comp_interval = 50; /* some sensible default? */
+
+ spin_lock_init(&env->comp_lock);
+ mutex_init(&env->read_lock);
+ init_completion(&env->done);
+ INIT_DELAYED_WORK(&env->comp_timeout, envelope_detector_timeout);
+
+ indio_dev->name = dev_name(dev);
+ indio_dev->dev.parent = dev;
+ indio_dev->dev.of_node = dev->of_node;
+ indio_dev->info = &envelope_detector_info;
+ indio_dev->channels = &envelope_detector_iio_channel;
+ indio_dev->num_channels = 1;
+
+ env->dac = devm_iio_channel_get(dev, "dac");
+ if (IS_ERR(env->dac)) {
+ if (PTR_ERR(env->dac) != -EPROBE_DEFER)
+ dev_err(dev, "failed to get dac input channel\n");
+ return PTR_ERR(env->dac);
+ }
+
+ env->comp_irq = platform_get_irq_byname(pdev, "comp");
+ if (env->comp_irq < 0) {
+ if (env->comp_irq != -EPROBE_DEFER)
+ dev_err(dev, "failed to get compare interrupt\n");
+ return env->comp_irq;
+ }
+
+ ret = devm_request_irq(dev, env->comp_irq, envelope_detector_comp_isr,
+ 0, "envelope-detector", env);
+ if (ret) {
+ if (ret != -EPROBE_DEFER)
+ dev_err(dev, "failed to request interrupt\n");
+ return ret;
+ }
+ env->comp_irq_trigger = irq_get_trigger_type(env->comp_irq);
+ if (env->comp_irq_trigger & IRQF_TRIGGER_RISING)
+ env->comp_irq_trigger_inv |= IRQF_TRIGGER_FALLING;
+ if (env->comp_irq_trigger & IRQF_TRIGGER_FALLING)
+ env->comp_irq_trigger_inv |= IRQF_TRIGGER_RISING;
+ if (env->comp_irq_trigger & IRQF_TRIGGER_HIGH)
+ env->comp_irq_trigger_inv |= IRQF_TRIGGER_LOW;
+ if (env->comp_irq_trigger & IRQF_TRIGGER_LOW)
+ env->comp_irq_trigger_inv |= IRQF_TRIGGER_HIGH;
+
+ ret = iio_get_channel_type(env->dac, &type);
+ if (ret < 0)
+ return ret;
+
+ if (type != IIO_VOLTAGE) {
+ dev_err(dev, "dac is of the wrong type\n");
+ return -EINVAL;
+ }
+
+ ret = iio_read_max_channel_raw(env->dac, &env->dac_max);
+ if (ret < 0) {
+ dev_err(dev, "dac does not indicate its raw maximum value\n");
+ return ret;
+ }
+
+ return devm_iio_device_register(dev, indio_dev);
+}
+
+static const struct of_device_id envelope_detector_match[] = {
+ { .compatible = "axentia,tse850-envelope-detector", },
+ { /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, envelope_detector_match);
+
+static struct platform_driver envelope_detector_driver = {
+ .probe = envelope_detector_probe,
+ .driver = {
+ .name = "iio-envelope-detector",
+ .of_match_table = envelope_detector_match,
+ },
+};
+module_platform_driver(envelope_detector_driver);
+
+MODULE_DESCRIPTION("Envelope detector using a DAC and a comparator");
+MODULE_AUTHOR("Peter Rosin <peda@axentia.se>");
+MODULE_LICENSE("GPL v2");
--
2.1.4