iio: dln2-adc: Fix lockdep complaint

When reading the voltage:

$ cat /sys/bus/iio/devices/iio\:device0/in_voltage0_raw

Lockdep complains:

[  153.910616] ======================================================
[  153.916918] WARNING: possible circular locking dependency detected
[  153.923221] 5.14.0+ #5 Not tainted
[  153.926692] ------------------------------------------------------
[  153.932992] cat/717 is trying to acquire lock:
[  153.937525] c2585358 (&indio_dev->mlock){+.+.}-{3:3}, at: iio_device_claim_direct_mode+0x28/0x44
[  153.946541]
               but task is already holding lock:
[  153.952487] c2585860 (&dln2->mutex){+.+.}-{3:3}, at: dln2_adc_read_raw+0x94/0x2bc [dln2_adc]
[  153.961152]
               which lock already depends on the new lock.

Fix this by not calling into the iio core underneath the dln2->mutex lock.

Fixes: 7c0299e ("iio: adc: Add support for DLN2 ADC")
Cc: Jack Andersen <jackoalan@gmail.com>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Link: https://lore.kernel.org/r/20211018113731.25723-1-noralf@tronnes.org
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/dln2-adc.c

@@ -248,7 +248,6 @@ static int dln2_adc_set_chan_period(struct dln2_adc *dln2,
 static int dln2_adc_read(struct dln2_adc *dln2, unsigned int channel)
 {
 	int ret, i;
-	struct iio_dev *indio_dev = platform_get_drvdata(dln2->pdev);
 	u16 conflict;
 	__le16 value;
 	int olen = sizeof(value);
@@ -257,13 +256,9 @@ static int dln2_adc_read(struct dln2_adc *dln2, unsigned int channel)
 		.chan = channel,
 	};
 
-	ret = iio_device_claim_direct_mode(indio_dev);
-	if (ret < 0)
-		return ret;
-
 	ret = dln2_adc_set_chan_enabled(dln2, channel, true);
 	if (ret < 0)
-		goto release_direct;
+		return ret;
 
 	ret = dln2_adc_set_port_enabled(dln2, true, &conflict);
 	if (ret < 0) {
@@ -300,8 +295,6 @@ static int dln2_adc_read(struct dln2_adc *dln2, unsigned int channel)
 	dln2_adc_set_port_enabled(dln2, false, NULL);
 disable_chan:
 	dln2_adc_set_chan_enabled(dln2, channel, false);
-release_direct:
-	iio_device_release_direct_mode(indio_dev);
 
 	return ret;
 }
@@ -337,10 +330,16 @@ static int dln2_adc_read_raw(struct iio_dev *indio_dev,
 
 	switch (mask) {
 	case IIO_CHAN_INFO_RAW:
+		ret = iio_device_claim_direct_mode(indio_dev);
+		if (ret < 0)
+			return ret;
+
 		mutex_lock(&dln2->mutex);
 		ret = dln2_adc_read(dln2, chan->channel);
 		mutex_unlock(&dln2->mutex);
 
+		iio_device_release_direct_mode(indio_dev);
+
 		if (ret < 0)
 			return ret;