iio: hid-sensor-als: Assign channels dynamically

Instead of assuming that every channel defined statically by
als_channels[] is present, assign dynamically based on presence of the
respective usage id in the descriptor. This will allow to register ALS
with limited channel support. Append the timestamp as the last channel.

Update available_scan_mask to specify all channels which are present.

There is no intentional function changes done.

Signed-off-by: Srinivas Pandruvada <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/iio/light/hid-sensor-als.c

···
 	struct hid_sensor_hub_callbacks callbacks;
 	struct hid_sensor_common common_attributes;
 	struct hid_sensor_hub_attribute_info als[CHANNEL_SCAN_INDEX_MAX];
+	struct iio_chan_spec channels[CHANNEL_SCAN_INDEX_MAX + 1];
 	struct {
 		u32 illum[CHANNEL_SCAN_INDEX_MAX];
 		u64 timestamp __aligned(8);
···
 	int scale_post_decml;
 	int scale_precision;
 	int value_offset;
+	int num_channels;
 	s64 timestamp;
+	unsigned long als_scan_mask[2];
+};
+
+/* The order of usage ids must match scan index starting from CHANNEL_SCAN_INDEX_INTENSITY */
+static const u32 als_usage_ids[] = {
+	HID_USAGE_SENSOR_LIGHT_ILLUM,
+	HID_USAGE_SENSOR_LIGHT_ILLUM,
 };
 
 static const u32 als_sensitivity_addresses[] = {
···
 /* Parse report which is specific to an usage id*/
 static int als_parse_report(struct platform_device *pdev,
 				struct hid_sensor_hub_device *hsdev,
-				struct iio_chan_spec *channels,
 				unsigned usage_id,
 				struct als_state *st)
 {
-	int ret;
+	struct iio_chan_spec *channels;
+	int ret, index = 0;
 	int i;
 
-	for (i = 0; i <= CHANNEL_SCAN_INDEX_ILLUM; ++i) {
+	channels = st->channels;
+
+	for (i = 0; i < CHANNEL_SCAN_INDEX_MAX; ++i) {
 		ret = sensor_hub_input_get_attribute_info(hsdev,
 						HID_INPUT_REPORT,
 						usage_id,
-						HID_USAGE_SENSOR_LIGHT_ILLUM,
+						als_usage_ids[i],
 						&st->als[i]);
 		if (ret < 0)
-			return ret;
-		als_adjust_channel_bit_mask(channels, i, st->als[i].size);
+			continue;
+
+		channels[index] = als_channels[i];
+		st->als_scan_mask[0] |= BIT(i);
+		als_adjust_channel_bit_mask(channels, index, st->als[i].size);
+		++index;
 
 		dev_dbg(&pdev->dev, "als %x:%x\n", st->als[i].index,
 			st->als[i].report_id);
 	}
+
+	st->num_channels = index;
+	/* Return success even if one usage id is present */
+	if (index)
+		ret = 0;
 
 	st->scale_precision = hid_sensor_format_scale(usage_id,
 				&st->als[CHANNEL_SCAN_INDEX_INTENSITY],
···
 		return ret;
 	}
 
-	indio_dev->channels = devm_kmemdup(&pdev->dev, als_channels,
-					   sizeof(als_channels), GFP_KERNEL);
-	if (!indio_dev->channels) {
-		dev_err(&pdev->dev, "failed to duplicate channels\n");
-		return -ENOMEM;
-	}
-
 	ret = als_parse_report(pdev, hsdev,
-			       (struct iio_chan_spec *)indio_dev->channels,
 			       hsdev->usage,
 			       als_state);
 	if (ret) {
···
 		return ret;
 	}
 
-	indio_dev->num_channels =
-				ARRAY_SIZE(als_channels);
+	/* Add timestamp channel */
+	als_state->channels[als_state->num_channels] = als_channels[CHANNEL_SCAN_INDEX_TIMESTAMP];
+
+	/* +1 for adding timestamp channel */
+	indio_dev->num_channels = als_state->num_channels + 1;
+
+	indio_dev->channels = als_state->channels;
+	indio_dev->available_scan_masks = als_state->als_scan_mask;
+
 	indio_dev->info = &als_info;
 	indio_dev->name = name;
 	indio_dev->modes = INDIO_DIRECT_MODE;