iio: acpi_als: Add trigger support

As some firmware does not notify on illuminance changes, add a
trigger to be able to query light via software (sysfs-trigger or
hrtrigger).
Add a hardware trigger set as the default trigger to maintain backward
compatibility.

Check iio_info reports the sensor as buffer capable:
  iio:device0: acpi-als (buffer capable)

To test, check we can get data on demand on an Intel based chromebook:

  IIO_DEV="iio:device0"
  echo 1 > iio_sysfs_trigger/add_trigger
  cat trigger2/name > ${IIO_DEV}/trigger/current_trigger
  for i in ${IIO_DEV}/scan_elements/*_en ${IIO_DEV}/buffer/enable ; do
    echo 1 > $i
  done
  od -x /dev/${IIO_DEV} &
  echo 1 > trigger2/trigger_now
Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20210317074012.2336454-4-gwendal@chromium.orgSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/light/acpi-als.c

@@ -16,11 +16,14 @@
 #include <linux/module.h>
 #include <linux/acpi.h>
 #include <linux/err.h>
+#include <linux/irq.h>
 #include <linux/mutex.h>
 
 #include <linux/iio/iio.h>
 #include <linux/iio/buffer.h>
-#include <linux/iio/kfifo_buf.h>
+#include <linux/iio/trigger.h>
+#include <linux/iio/triggered_buffer.h>
+#include <linux/iio/trigger_consumer.h>
 
 #define ACPI_ALS_CLASS			"als"
 #define ACPI_ALS_DEVICE_NAME		"acpi-als"
@@ -59,6 +62,7 @@ static const struct iio_chan_spec acpi_als_channels[] = {
 struct acpi_als {
 	struct acpi_device	*device;
 	struct mutex		lock;
+	struct iio_trigger	*trig;
 
 	s32 evt_buffer[ACPI_ALS_EVT_BUFFER_SIZE / sizeof(s32)]  __aligned(8);
 };
@@ -102,33 +106,19 @@ static void acpi_als_notify(struct acpi_device *device, u32 event)
 {
 	struct iio_dev *indio_dev = acpi_driver_data(device);
 	struct acpi_als *als = iio_priv(indio_dev);
-	s32 *buffer = als->evt_buffer;
-	s64 time_ns = iio_get_time_ns(indio_dev);
-	s32 val;
-	int ret;
-
-	mutex_lock(&als->lock);
-
-	memset(buffer, 0, ACPI_ALS_EVT_BUFFER_SIZE);
 
+	if (iio_buffer_enabled(indio_dev) && iio_trigger_using_own(indio_dev)) {
 		switch (event) {
 		case ACPI_ALS_NOTIFY_ILLUMINANCE:
-		ret = acpi_als_read_value(als, ACPI_ALS_ILLUMINANCE, &val);
-		if (ret < 0)
-			goto out;
-		*buffer++ = val;
+			iio_trigger_poll_chained(als->trig);
 			break;
 		default:
 			/* Unhandled event */
-		dev_dbg(&device->dev, "Unhandled ACPI ALS event (%08x)!\n",
+			dev_dbg(&device->dev,
+				"Unhandled ACPI ALS event (%08x)!\n",
 				event);
-		goto out;
 		}
-
-	iio_push_to_buffers_with_timestamp(indio_dev, als->evt_buffer, time_ns);
-
-out:
-	mutex_unlock(&als->lock);
+	}
 }
 
 static int acpi_als_read_raw(struct iio_dev *indio_dev,
@@ -159,6 +149,41 @@ static const struct iio_info acpi_als_info = {
 	.read_raw		= acpi_als_read_raw,
 };
 
+static irqreturn_t acpi_als_trigger_handler(int irq, void *p)
+{
+	struct iio_poll_func *pf = p;
+	struct iio_dev *indio_dev = pf->indio_dev;
+	struct acpi_als *als = iio_priv(indio_dev);
+	s32 *buffer = als->evt_buffer;
+	s32 val;
+	int ret;
+
+	mutex_lock(&als->lock);
+
+	ret = acpi_als_read_value(als, ACPI_ALS_ILLUMINANCE, &val);
+	if (ret < 0)
+		goto out;
+	*buffer = val;
+
+	/*
+	 * When coming from own trigger via polls, set polling function
+	 * timestamp here. Given ACPI notifier is already in a thread and call
+	 * function directly, there is no need to set the timestamp in the
+	 * notify function.
+	 *
+	 * If the timestamp was actually 0, the timestamp is set one more time.
+	 */
+	if (!pf->timestamp)
+		pf->timestamp = iio_get_time_ns(indio_dev);
+
+	iio_push_to_buffers_with_timestamp(indio_dev, buffer, pf->timestamp);
+out:
+	mutex_unlock(&als->lock);
+	iio_trigger_notify_done(indio_dev->trig);
+
+	return IRQ_HANDLED;
+}
+
 static int acpi_als_add(struct acpi_device *device)
 {
 	struct device *dev = &device->dev;
@@ -181,8 +206,23 @@ static int acpi_als_add(struct acpi_device *device)
 	indio_dev->channels = acpi_als_channels;
 	indio_dev->num_channels = ARRAY_SIZE(acpi_als_channels);
 
-	ret = devm_iio_kfifo_buffer_setup(dev, indio_dev,
-					  INDIO_BUFFER_SOFTWARE, NULL);
+	als->trig = devm_iio_trigger_alloc(dev, "%s-dev%d", indio_dev->name, indio_dev->id);
+	if (!als->trig)
+		return -ENOMEM;
+
+	ret = devm_iio_trigger_register(dev, als->trig);
+	if (ret)
+		return ret;
+	/*
+	 * Set hardware trigger by default to let events flow when
+	 * BIOS support notification.
+	 */
+	indio_dev->trig = iio_trigger_get(als->trig);
+
+	ret = devm_iio_triggered_buffer_setup(dev, indio_dev,
+					      iio_pollfunc_store_time,
+					      acpi_als_trigger_handler,
+					      NULL);
 	if (ret)
 		return ret;