iio: Require strict scan mask matching in hardware mode

In hardware mode we can not use the software demuxer, this means that the
selected scan mask needs to match one of the available scan masks exactly.

It also means that all attached buffers need to use the same scan mask.
Given that when operating in hardware mode there is typically only a single
buffer attached to the device this not an issue. Add a sanity check to make
sure that only a single buffer is attached in hardware mode nevertheless.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/industrialio-buffer.c

@@ -239,13 +239,19 @@ static ssize_t iio_scan_el_show(struct device *dev,
 /* Note NULL used as error indicator as it doesn't make sense. */
 static const unsigned long *iio_scan_mask_match(const unsigned long *av_masks,
 					  unsigned int masklength,
-					  const unsigned long *mask)
+					  const unsigned long *mask,
+					  bool strict)
 {
 	if (bitmap_empty(mask, masklength))
 		return NULL;
 	while (*av_masks) {
-		if (bitmap_subset(mask, av_masks, masklength))
-			return av_masks;
+		if (strict) {
+			if (bitmap_equal(mask, av_masks, masklength))
+				return av_masks;
+		} else {
+			if (bitmap_subset(mask, av_masks, masklength))
+				return av_masks;
+		}
 		av_masks += BITS_TO_LONGS(masklength);
 	}
 	return NULL;
@@ -295,7 +301,7 @@ static int iio_scan_mask_set(struct iio_dev *indio_dev,
 	if (indio_dev->available_scan_masks) {
 		mask = iio_scan_mask_match(indio_dev->available_scan_masks,
 					   indio_dev->masklength,
-					   trialmask);
+					   trialmask, false);
 		if (!mask)
 			goto err_invalid_mask;
 	}
@@ -602,6 +608,7 @@ static int iio_verify_update(struct iio_dev *indio_dev,
 {
 	unsigned long *compound_mask;
 	const unsigned long *scan_mask;
+	bool strict_scanmask = false;
 	struct iio_buffer *buffer;
 	bool scan_timestamp;
 	unsigned int modes;
@@ -631,7 +638,14 @@ static int iio_verify_update(struct iio_dev *indio_dev,
 	if ((modes & INDIO_BUFFER_TRIGGERED) && indio_dev->trig) {
 		config->mode = INDIO_BUFFER_TRIGGERED;
 	} else if (modes & INDIO_BUFFER_HARDWARE) {
+		/*
+		 * Keep things simple for now and only allow a single buffer to
+		 * be connected in hardware mode.
+		 */
+		if (insert_buffer && !list_empty(&indio_dev->buffer_list))
+			return -EINVAL;
 		config->mode = INDIO_BUFFER_HARDWARE;
+		strict_scanmask = true;
 	} else if (modes & INDIO_BUFFER_SOFTWARE) {
 		config->mode = INDIO_BUFFER_SOFTWARE;
 	} else {
@@ -666,7 +680,8 @@ static int iio_verify_update(struct iio_dev *indio_dev,
 	if (indio_dev->available_scan_masks) {
 		scan_mask = iio_scan_mask_match(indio_dev->available_scan_masks,
 				    indio_dev->masklength,
-				    compound_mask);
+				    compound_mask,
+				    strict_scanmask);
 		kfree(compound_mask);
 		if (scan_mask == NULL)
 			return -EINVAL;