[PATCH v8 4/6] iio: ABI: Add support for floating-point numbers in buffer scan elements

[Francesco Lavra <flavra@baylibre.com>]

In the data storage description of a scan element, the first character
after the colon can have the values 's' and 'u' to specify signed and
unsigned integers, respectively.
Add 'f' as an allowed value to specify floating-point numbers formatted
according to the IEEE 754 standard.

Signed-off-by: Francesco Lavra <flavra@baylibre.com>
---
 Documentation/ABI/testing/sysfs-bus-iio  | 33 +++++++++++++-----------
 Documentation/driver-api/iio/buffers.rst |  3 ++-
 Documentation/iio/iio_devbuf.rst         |  3 ++-
 include/linux/iio/iio.h                  |  2 ++
 4 files changed, 24 insertions(+), 17 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-bus-iio b/Documentation/ABI/testing/sysfs-bus-iio
index 5f87dcee78f7..bd6c3305dd2b 100644
--- a/Documentation/ABI/testing/sysfs-bus-iio
+++ b/Documentation/ABI/testing/sysfs-bus-iio
@@ -1510,21 +1510,24 @@ Contact:	linux-iio@vger.kernel.org
 Description:
 		Description of the scan element data storage within the buffer
 		and hence the form in which it is read from user-space.
-		Form is [be|le]:[s|u]bits/storagebits[>>shift].
-		be or le specifies big or little endian. s or u specifies if
-		signed (2's complement) or unsigned. bits is the number of bits
-		of data and storagebits is the space (after padding) that it
-		occupies in the buffer. shift if specified, is the shift that
-		needs to be applied prior to masking out unused bits. Some
-		devices put their data in the middle of the transferred elements
-		with additional information on both sides.  Note that some
-		devices will have additional information in the unused bits
-		so to get a clean value, the bits value must be used to mask
-		the buffer output value appropriately.  The storagebits value
-		also specifies the data alignment.  So s48/64>>2 will be a
-		signed 48 bit integer stored in a 64 bit location aligned to
-		a 64 bit boundary. To obtain the clean value, shift right 2
-		and apply a mask to zero the top 16 bits of the result.
+		Form is [be|le]:[f|s|u]bits/storagebits[>>shift].
+		be or le specifies big or little endian. f means floating-point
+		(IEEE 754 binary format), s means signed (2's complement), u means
+		unsigned. bits is the number of bits of data and storagebits is the
+		space (after padding) that it occupies in the buffer; when using a
+		floating-point format, bits must be one of the width values defined
+		in the IEEE 754 standard for binary interchange formats (e.g. 16
+		indicates the binary16 format for half-precision numbers). shift,
+		if specified, is the shift that needs to be applied prior to
+		masking out unused bits. Some devices put their data in the middle
+		of the transferred elements with additional information on both
+		sides. Note that some devices will have additional information in
+		the unused bits, so to get a clean value the bits value must be
+		used to mask the buffer output value appropriately. The storagebits
+		value also specifies the data alignment. So s48/64>>2 will be a
+		signed 48 bit integer stored in a 64 bit location aligned to a 64
+		bit boundary. To obtain the clean value, shift right 2 and apply a
+		mask to zero the top 16 bits of the result.
 		For other storage combinations this attribute will be extended
 		appropriately.
 
diff --git a/Documentation/driver-api/iio/buffers.rst b/Documentation/driver-api/iio/buffers.rst
index e16abaf826fe..8779022e3da5 100644
--- a/Documentation/driver-api/iio/buffers.rst
+++ b/Documentation/driver-api/iio/buffers.rst
@@ -37,9 +37,10 @@ directory contains attributes of the following form:
 * :file:`index`, the scan_index of the channel.
 * :file:`type`, description of the scan element data storage within the buffer
   and hence the form in which it is read from user space.
-  Format is [be|le]:[s|u]bits/storagebits[Xrepeat][>>shift] .
+  Format is [be|le]:[f|s|u]bits/storagebits[Xrepeat][>>shift] .
 
   * *be* or *le*, specifies big or little endian.
+  * *f*, specifies if floating-point.
   * *s* or *u*, specifies if signed (2's complement) or unsigned.
   * *bits*, is the number of valid data bits.
   * *storagebits*, is the number of bits (after padding) that it occupies in the
diff --git a/Documentation/iio/iio_devbuf.rst b/Documentation/iio/iio_devbuf.rst
index dca1f0200b0d..e91730fa3cea 100644
--- a/Documentation/iio/iio_devbuf.rst
+++ b/Documentation/iio/iio_devbuf.rst
@@ -83,9 +83,10 @@ and the relevant _type attributes to establish the data storage format.
 
 Read-only attribute containing the description of the scan element data storage
 within the buffer and hence the form in which it is read from userspace. Format
-is [be|le]:[s|u]bits/storagebits[Xrepeat][>>shift], where:
+is [be|le]:[f|s|u]bits/storagebits[Xrepeat][>>shift], where:
 
 - **be** or **le** specifies big or little-endian.
+- **f** specifies if floating-point.
 - **s** or **u** specifies if signed (2's complement) or unsigned.
 - **bits** is the number of valid data bits.
 - **storagebits** is the number of bits (after padding) that it occupies in the
diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
index d48a0ab01b8d..1f2c1cb03394 100644
--- a/include/linux/iio/iio.h
+++ b/include/linux/iio/iio.h
@@ -180,9 +180,11 @@ struct iio_event_spec {
  * Format values in scan type
  * @IIO_SCAN_FORMAT_SIGNED_INT: Signed integer (two's complement).
  * @IIO_SCAN_FORMAT_UNSIGNED_INT: Unsigned integer.
+ * @IIO_SCAN_FORMAT_FLOAT: Floating point.
  */
 #define IIO_SCAN_FORMAT_SIGNED_INT	's'
 #define IIO_SCAN_FORMAT_UNSIGNED_INT	'u'
+#define IIO_SCAN_FORMAT_FLOAT		'f'
 
 /**
  * struct iio_scan_type - specification for channel data format in buffer
-- 
2.39.5