iio: dummy: Use automatic lock and direct mode cleanup.

Given we now have iio_device_claim_direct_scoped() to perform automatic
releasing of direct mode at exit from the scope that follows it, this can
be used in conjunction with guard(mutex) etc remove a lot of special case
handling.

Note that in this particular example code, there is no real reason you can't
read channels via sysfs at the same time as filling the software buffer.
To make it look more like a real driver constrain raw and processed
channel reads from occurring whilst the buffer is in use.
Reviewed-by: David Lechner <dlechner@baylibre.com>
Reviewed-by: Nuno Sa <nuno.a@analog.com>
Link: https://lore.kernel.org/r/20240128150537.44592-3-jic23@kernel.orgSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/dummy/iio_simple_dummy.c

@@ -283,65 +283,63 @@ static int iio_dummy_read_raw(struct iio_dev *indio_dev,
 			      long mask)
 {
 	struct iio_dummy_state *st = iio_priv(indio_dev);
-	int ret = -EINVAL;
 
-	mutex_lock(&st->lock);
 	switch (mask) {
 	case IIO_CHAN_INFO_RAW: /* magic value - channel value read */
+		iio_device_claim_direct_scoped(return -EBUSY, indio_dev) {
+			guard(mutex)(&st->lock);
 			switch (chan->type) {
 			case IIO_VOLTAGE:
 				if (chan->output) {
 					/* Set integer part to cached value */
 					*val = st->dac_val;
-				ret = IIO_VAL_INT;
+					return IIO_VAL_INT;
 				} else if (chan->differential) {
 					if (chan->channel == 1)
 						*val = st->differential_adc_val[0];
 					else
 						*val = st->differential_adc_val[1];
-				ret = IIO_VAL_INT;
+					return IIO_VAL_INT;
 				} else {
 					*val = st->single_ended_adc_val;
-				ret = IIO_VAL_INT;
+					return IIO_VAL_INT;
 				}
-			break;
+
 			case IIO_ACCEL:
 				*val = st->accel_val;
-			ret = IIO_VAL_INT;
-			break;
+				return IIO_VAL_INT;
 			default:
-			break;
+				return -EINVAL;
 			}
-		break;
+		}
+		unreachable();
 	case IIO_CHAN_INFO_PROCESSED:
+		iio_device_claim_direct_scoped(return -EBUSY, indio_dev) {
+			guard(mutex)(&st->lock);
 			switch (chan->type) {
 			case IIO_STEPS:
 				*val = st->steps;
-			ret = IIO_VAL_INT;
-			break;
+				return IIO_VAL_INT;
 			case IIO_ACTIVITY:
 				switch (chan->channel2) {
 				case IIO_MOD_RUNNING:
 					*val = st->activity_running;
-				ret = IIO_VAL_INT;
-				break;
+					return IIO_VAL_INT;
 				case IIO_MOD_WALKING:
 					*val = st->activity_walking;
-				ret = IIO_VAL_INT;
-				break;
+					return IIO_VAL_INT;
 				default:
-				break;
+					return -EINVAL;
 				}
-			break;
 			default:
-			break;
+				return -EINVAL;
 			}
-		break;
+		}
+		unreachable();
 	case IIO_CHAN_INFO_OFFSET:
 		/* only single ended adc -> 7 */
 		*val = 7;
-		ret = IIO_VAL_INT;
-		break;
+		return IIO_VAL_INT;
 	case IIO_CHAN_INFO_SCALE:
 		switch (chan->type) {
 		case IIO_VOLTAGE:
@@ -350,60 +348,57 @@ static int iio_dummy_read_raw(struct iio_dev *indio_dev,
 				/* only single ended adc -> 0.001333 */
 				*val = 0;
 				*val2 = 1333;
-				ret = IIO_VAL_INT_PLUS_MICRO;
-				break;
+				return IIO_VAL_INT_PLUS_MICRO;
 			case 1:
 				/* all differential adc -> 0.000001344 */
 				*val = 0;
 				*val2 = 1344;
-				ret = IIO_VAL_INT_PLUS_NANO;
+				return IIO_VAL_INT_PLUS_NANO;
+			default:
+				return -EINVAL;
 			}
-			break;
 		default:
-			break;
+			return -EINVAL;
 		}
-		break;
-	case IIO_CHAN_INFO_CALIBBIAS:
+	case IIO_CHAN_INFO_CALIBBIAS: {
+		guard(mutex)(&st->lock);
 		/* only the acceleration axis - read from cache */
 		*val = st->accel_calibbias;
-		ret = IIO_VAL_INT;
-		break;
-	case IIO_CHAN_INFO_CALIBSCALE:
+		return IIO_VAL_INT;
+	}
+	case IIO_CHAN_INFO_CALIBSCALE: {
+		guard(mutex)(&st->lock);
 		*val = st->accel_calibscale->val;
 		*val2 = st->accel_calibscale->val2;
-		ret = IIO_VAL_INT_PLUS_MICRO;
-		break;
+		return IIO_VAL_INT_PLUS_MICRO;
+	}
 	case IIO_CHAN_INFO_SAMP_FREQ:
 		*val = 3;
 		*val2 = 33;
-		ret = IIO_VAL_INT_PLUS_NANO;
-		break;
-	case IIO_CHAN_INFO_ENABLE:
+		return IIO_VAL_INT_PLUS_NANO;
+	case IIO_CHAN_INFO_ENABLE: {
+		guard(mutex)(&st->lock);
 		switch (chan->type) {
 		case IIO_STEPS:
 			*val = st->steps_enabled;
-			ret = IIO_VAL_INT;
-			break;
+			return IIO_VAL_INT;
 		default:
-			break;
+			return -EINVAL;
 		}
-		break;
-	case IIO_CHAN_INFO_CALIBHEIGHT:
+	}
+	case IIO_CHAN_INFO_CALIBHEIGHT: {
+		guard(mutex)(&st->lock);
 		switch (chan->type) {
 		case IIO_STEPS:
 			*val = st->height;
-			ret = IIO_VAL_INT;
-			break;
+			return IIO_VAL_INT;
 		default:
-			break;
+			return -EINVAL;
+		}
 	}
-		break;
-
 	default:
-		break;
+		return -EINVAL;
 	}
-	mutex_unlock(&st->lock);
-	return ret;
 }
 
 /**
@@ -426,7 +421,6 @@ static int iio_dummy_write_raw(struct iio_dev *indio_dev,
 			       long mask)
 {
 	int i;
-	int ret = 0;
 	struct iio_dummy_state *st = iio_priv(indio_dev);
 
 	switch (mask) {
@@ -436,10 +430,10 @@ static int iio_dummy_write_raw(struct iio_dev *indio_dev,
 			if (chan->output == 0)
 				return -EINVAL;
 
+			scoped_guard(mutex, &st->lock) {
 				/* Locking not required as writing single value */
-			mutex_lock(&st->lock);
 				st->dac_val = val;
-			mutex_unlock(&st->lock);
+			}
 			return 0;
 		default:
 			return -EINVAL;
@@ -447,9 +441,9 @@ static int iio_dummy_write_raw(struct iio_dev *indio_dev,
 	case IIO_CHAN_INFO_PROCESSED:
 		switch (chan->type) {
 		case IIO_STEPS:
-			mutex_lock(&st->lock);
+			scoped_guard(mutex, &st->lock) {
 				st->steps = val;
-			mutex_unlock(&st->lock);
+			}
 			return 0;
 		case IIO_ACTIVITY:
 			if (val < 0)
@@ -470,30 +464,29 @@ static int iio_dummy_write_raw(struct iio_dev *indio_dev,
 		default:
 			return -EINVAL;
 		}
-	case IIO_CHAN_INFO_CALIBSCALE:
-		mutex_lock(&st->lock);
+	case IIO_CHAN_INFO_CALIBSCALE: {
+		guard(mutex)(&st->lock);
 		/* Compare against table - hard matching here */
 		for (i = 0; i < ARRAY_SIZE(dummy_scales); i++)
 			if (val == dummy_scales[i].val &&
 			    val2 == dummy_scales[i].val2)
 				break;
 		if (i == ARRAY_SIZE(dummy_scales))
-			ret = -EINVAL;
-		else
+			return -EINVAL;
 		st->accel_calibscale = &dummy_scales[i];
-		mutex_unlock(&st->lock);
-		return ret;
+		return 0;
+	}
 	case IIO_CHAN_INFO_CALIBBIAS:
-		mutex_lock(&st->lock);
+		scoped_guard(mutex, &st->lock) {
 			st->accel_calibbias = val;
-		mutex_unlock(&st->lock);
+		}
 		return 0;
 	case IIO_CHAN_INFO_ENABLE:
 		switch (chan->type) {
 		case IIO_STEPS:
-			mutex_lock(&st->lock);
+			scoped_guard(mutex, &st->lock) {
 				st->steps_enabled = val;
-			mutex_unlock(&st->lock);
+			}
 			return 0;
 		default:
 			return -EINVAL;