iio: proximity: as3935: noise detection + threshold changes

Most applications are too noisy to allow the default noise and
watchdog settings, and thus need to be configurable via DT
properties.

Also default settings to POR defaults on a reset, and register
distuber interrupts as noise since it prevents proper usage.

Cc: [e-mail]
Signed-off-by: Matt Ranostay <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Signed-off-by: Jonathan Cameron <[e-mail]>

Documentation/ABI/testing/sysfs-bus-iio-proximity-as3935

···
 		Show or set the gain boost of the amp, from 0-31 range.
 		18 = indoors (default)
 		14 = outdoors
+
+What		/sys/bus/iio/devices/iio:deviceX/noise_level_tripped
+Date:		May 2017
+KernelVersion:	4.13
+Contact:	Matt Ranostay <[e-mail]>
+Description:
+		When 1 the noise level is over the trip level and not reporting
+		valid data

Documentation/devicetree/bindings/iio/proximity/as3935.txt

···
 	- ams,tuning-capacitor-pf: Calibration tuning capacitor stepping
 	  value 0 - 120pF. This will require using the calibration data from
 	  the manufacturer.
+	- ams,nflwdth: Set the noise and watchdog threshold register on
+	  startup. This will need to set according to the noise from the
+	  MCU board, and possibly the local environment. Refer to the
+	  datasheet for the threshold settings.
 
 Example:
 
···
 	interrupt-parent = <&gpio1>;
 	interrupts = <16 1>;
 	ams,tuning-capacitor-pf = <80>;
+	ams,nflwdth = <0x44>;
 };

drivers/iio/proximity/as3935.c

···
 #define AS3935_AFE_GAIN_MAX	0x1F
 #define AS3935_AFE_PWR_BIT	BIT(0)
 
+#define AS3935_NFLWDTH		0x01
+#define AS3935_NFLWDTH_MASK	0x7f
+
 #define AS3935_INT		0x03
 #define AS3935_INT_MASK		0x0f
+#define AS3935_DISTURB_INT	BIT(2)
 #define AS3935_EVENT_INT	BIT(3)
 #define AS3935_NOISE_INT	BIT(0)
 
···
 #define AS3935_DATA_MASK	0x3F
 
 #define AS3935_TUNE_CAP		0x08
+#define AS3935_DEFAULTS		0x3C
 #define AS3935_CALIBRATE	0x3D
 
 #define AS3935_READ_DATA	BIT(14)
···
 	struct mutex lock;
 	struct delayed_work work;
 
+	unsigned long noise_tripped;
 	u32 tune_cap;
+	u32 nflwdth_reg;
 	u8 buffer[16]; /* 8-bit data + 56-bit padding + 64-bit timestamp */
 	u8 buf[2] ____cacheline_aligned;
 };
···
 	return len;
 }
 
+static ssize_t as3935_noise_level_tripped_show(struct device *dev,
+					struct device_attribute *attr,
+					char *buf)
+{
+	struct as3935_state *st = iio_priv(dev_to_iio_dev(dev));
+	int ret;
+
+	mutex_lock(&st->lock);
+	ret = sprintf(buf, "%d\n", !time_after(jiffies, st->noise_tripped + HZ));
+	mutex_unlock(&st->lock);
+
+	return ret;
+}
+
 static IIO_DEVICE_ATTR(sensor_sensitivity, S_IRUGO | S_IWUSR,
 	as3935_sensor_sensitivity_show, as3935_sensor_sensitivity_store, 0);
 
+static IIO_DEVICE_ATTR(noise_level_tripped, S_IRUGO,
+	as3935_noise_level_tripped_show, NULL, 0);
 
 static struct attribute *as3935_attributes[] = {
 	&iio_dev_attr_sensor_sensitivity.dev_attr.attr,
+	&iio_dev_attr_noise_level_tripped.dev_attr.attr,
 	NULL,
 };
 
···
 	case AS3935_EVENT_INT:
 		iio_trigger_poll_chained(st->trig);
 		break;
+	case AS3935_DISTURB_INT:
 	case AS3935_NOISE_INT:
+		mutex_lock(&st->lock);
+		st->noise_tripped = jiffies;
+		mutex_unlock(&st->lock);
 		dev_warn(&st->spi->dev, "noise level is too high\n");
 		break;
 	}
···
 
 static void calibrate_as3935(struct as3935_state *st)
 {
-	/* mask disturber interrupt bit */
-	as3935_write(st, AS3935_INT, BIT(5));
-
+	as3935_write(st, AS3935_DEFAULTS, 0x96);
 	as3935_write(st, AS3935_CALIBRATE, 0x96);
 	as3935_write(st, AS3935_TUNE_CAP,
 		BIT(5) | (st->tune_cap / TUNE_CAP_DIV));
 
 	mdelay(2);
 	as3935_write(st, AS3935_TUNE_CAP, (st->tune_cap / TUNE_CAP_DIV));
+	as3935_write(st, AS3935_NFLWDTH, st->nflwdth_reg);
 }
 
 #ifdef CONFIG_PM_SLEEP
···
 		return -EINVAL;
 	}
 
+	ret = of_property_read_u32(np,
+			"ams,nflwdth", &st->nflwdth_reg);
+	if (!ret && st->nflwdth_reg > AS3935_NFLWDTH_MASK) {
+		dev_err(&spi->dev,
+			"invalid nflwdth setting of %d\n",
+			st->nflwdth_reg);
+		return -EINVAL;
+	}
+
 	indio_dev->dev.parent = &spi->dev;
 	indio_dev->name = spi_get_device_id(spi)->name;
 	indio_dev->channels = as3935_channels;
···
 		return -ENOMEM;
 
 	st->trig = trig;
+	st->noise_tripped = jiffies - HZ;
 	trig->dev.parent = indio_dev->dev.parent;
 	iio_trigger_set_drvdata(trig, indio_dev);
 	trig->ops = &iio_interrupt_trigger_ops;