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 <[email protected]>
Signed-off-by: Noralf Trønnes <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Cc: <[email protected]>
Signed-off-by: Jonathan Cameron <[email protected]>

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;