iio: Add callback to check whether a scan mask is valid

This is useful for cases where the number of valid scan masks grows
exponentially, but it is rather easy to check whether a mask is valid or not
programmatically.

An example of such a case is a device with multiple ADCs where each ADC has a
upstream MUX, which allows to select from a number of physical channels.

  +-------+   +-------+
  |       |   |       | --- Channel 1
  | ADC 1 |---| MUX 1 | ---   ...
  |       |   |       | --- Channel M
  +-------+   +-------+

     .            .            .
     .            .            .
     .            .            .

  +-------+   +-------+
  |       |   |       | --- Channel M * N + 1
  | ADC N |---| MUX N | ---       ...
  |       |   |       | --- Channel M * N + M
  +-------+   +-------+

The number of necessary scan masks for this case is (M+1)**N - 1, on the other
hand it is easy to check whether subsets for each ADC of the scanmask have only
one bit set.

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

1 files changed, 4 insertions, 0 deletions

diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
index 2afbb6f01af..be82936c408 100644
--- a/include/linux/iio/iio.h
+++ b/include/linux/iio/iio.h
@@ -363,12 +363,16 @@ struct iio_info {
  * @predisable:		[DRIVER] function to run prior to marking buffer
  *			disabled
  * @postdisable:	[DRIVER] function to run after marking buffer disabled
+ * @validate_scan_mask: [DRIVER] function callback to check whether a given
+ *			scan mask is valid for the device.
  */
 struct iio_buffer_setup_ops {
 	int				(*preenable)(struct iio_dev *);
 	int				(*postenable)(struct iio_dev *);
 	int				(*predisable)(struct iio_dev *);
 	int				(*postdisable)(struct iio_dev *);
+	bool (*validate_scan_mask)(struct iio_dev *indio_dev,
+				   const unsigned long *scan_mask);
 };
 
 /**