// SPDX-License-Identifier: GPL-2.0 /* * Driver for an envelope detector using a DAC and a comparator * * Copyright (C) 2016 Axentia Technologies AB * * Author: Peter Rosin */ /* * 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 #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include 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, }; 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 "); MODULE_LICENSE("GPL v2");