[PATCH v8 2/6] iio: Replace 'sign' field with union in struct iio_scan_type

[Francesco Lavra <flavra@baylibre.com>]

This field is used to differentiate between signed and unsigned integers.
A following commit will extend its use in order to add support for non-
integer scan elements; therefore, replace it with a union that contains a
more generic 'format' field. This union will be dropped when all drivers
are changed to use the format field.
Opportunistically replace character literals with symbolic constants that
represent the set of allowed values for the format field.

Signed-off-by: Francesco Lavra <flavra@baylibre.com>
---
 Documentation/driver-api/iio/buffers.rst |  4 ++--
 include/linux/iio/iio.h                  | 17 +++++++++++++++--
 2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/Documentation/driver-api/iio/buffers.rst b/Documentation/driver-api/iio/buffers.rst
index 63f364e862d1..e16abaf826fe 100644
--- a/Documentation/driver-api/iio/buffers.rst
+++ b/Documentation/driver-api/iio/buffers.rst
@@ -78,7 +78,7 @@ fields in iio_chan_spec definition::
    /* other members */
            int scan_index
            struct {
-                   char sign;
+                   char format;
                    u8 realbits;
                    u8 storagebits;
                    u8 shift;
@@ -98,7 +98,7 @@ following channel definition::
 		   /* other stuff here */
 		   .scan_index = 0,
 		   .scan_type = {
-		           .sign = 's',
+		           .format = IIO_SCAN_FORMAT_SIGNED_INT,
 			   .realbits = 12,
 			   .storagebits = 16,
 			   .shift = 4,
diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
index a9ecff191bd9..d48a0ab01b8d 100644
--- a/include/linux/iio/iio.h
+++ b/include/linux/iio/iio.h
@@ -176,9 +176,19 @@ struct iio_event_spec {
 	unsigned long mask_shared_by_all;
 };
 
+/*
+ * Format values in scan type
+ * @IIO_SCAN_FORMAT_SIGNED_INT: Signed integer (two's complement).
+ * @IIO_SCAN_FORMAT_UNSIGNED_INT: Unsigned integer.
+ */
+#define IIO_SCAN_FORMAT_SIGNED_INT	's'
+#define IIO_SCAN_FORMAT_UNSIGNED_INT	'u'
+
 /**
  * struct iio_scan_type - specification for channel data format in buffer
- * @sign:		's' or 'u' to specify signed or unsigned
+ * @sign:		Deprecated, use @format instead.
+ * @format:		Data format, can have any of the IIO_SCAN_FORMAT_*
+ *			values.
  * @realbits:		Number of valid bits of data
  * @storagebits:	Realbits + padding
  * @shift:		Shift right by this before masking out realbits.
@@ -189,7 +199,10 @@ struct iio_event_spec {
  * @endianness:		little or big endian
  */
 struct iio_scan_type {
-	char	sign;
+	union {
+		char sign;
+		char format;
+	};
 	u8	realbits;
 	u8	storagebits;
 	u8	shift;
-- 
2.39.5