Cache the offset (in bytes) for the timestamp element in a scan buffer.
This will be used later to ensure proper alignment of the timestamp
element in the scan buffer.

The new field could not be placed in struct iio_dev_opaque because we
will need to access it in a static inline function later, so we make it
__private instead. It is only intended to be used by core IIO code.

Signed-off-by: David Lechner <dlechner@baylibre.com>
---

v2 changes:
* Cache the timestamp offset instead of the largest scan element size.
---
 drivers/iio/industrialio-buffer.c | 14 +++++++++++---
 include/linux/iio/iio.h           |  3 +++
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
index 4e413b4bb073..ecfe0c9740e2 100644
--- a/drivers/iio/industrialio-buffer.c
+++ b/drivers/iio/industrialio-buffer.c
@@ -763,7 +763,8 @@ static int iio_storage_bytes_for_timestamp(struct iio_dev *indio_dev)
 
 static int iio_compute_scan_bytes(struct iio_dev *indio_dev,
 				  const unsigned long *mask, bool timestamp,
-				  unsigned int *scan_bytes)
+				  unsigned int *scan_bytes,
+				  unsigned int *timestamp_offset)
 {
 	unsigned int bytes = 0;
 	int length, i, largest = 0;
@@ -785,6 +786,10 @@ static int iio_compute_scan_bytes(struct iio_dev *indio_dev,
 			return length;
 
 		bytes = ALIGN(bytes, length);
+
+		if (timestamp_offset)
+			*timestamp_offset = bytes;
+
 		bytes += length;
 		largest = max(largest, length);
 	}
@@ -846,7 +851,7 @@ static int iio_buffer_update_bytes_per_datum(struct iio_dev *indio_dev,
 		return 0;
 
 	ret = iio_compute_scan_bytes(indio_dev, buffer->scan_mask,
-				     buffer->scan_timestamp, &bytes);
+				     buffer->scan_timestamp, &bytes, NULL);
 	if (ret)
 		return ret;
 
@@ -890,6 +895,7 @@ struct iio_device_config {
 	unsigned int watermark;
 	const unsigned long *scan_mask;
 	unsigned int scan_bytes;
+	unsigned int scan_timestamp_offset;
 	bool scan_timestamp;
 };
 
@@ -995,7 +1001,8 @@ static int iio_verify_update(struct iio_dev *indio_dev,
 	}
 
 	ret = iio_compute_scan_bytes(indio_dev, scan_mask, scan_timestamp,
-				     &config->scan_bytes);
+				     &config->scan_bytes,
+				     &config->scan_timestamp_offset);
 	if (ret)
 		return ret;
 
@@ -1153,6 +1160,7 @@ static int iio_enable_buffers(struct iio_dev *indio_dev,
 	indio_dev->active_scan_mask = config->scan_mask;
 	ACCESS_PRIVATE(indio_dev, scan_timestamp) = config->scan_timestamp;
 	indio_dev->scan_bytes = config->scan_bytes;
+	ACCESS_PRIVATE(indio_dev, scan_timestamp_offset) = config->scan_timestamp_offset;
 	iio_dev_opaque->currentmode = config->mode;
 
 	iio_update_demux(indio_dev);
diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
index 2c91b7659ce9..ecbaeecbe0ac 100644
--- a/include/linux/iio/iio.h
+++ b/include/linux/iio/iio.h
@@ -584,6 +584,8 @@ struct iio_buffer_setup_ops {
  *			and owner
  * @buffer:		[DRIVER] any buffer present
  * @scan_bytes:		[INTERN] num bytes captured to be fed to buffer demux
+ * @scan_timestamp_offset: [INTERN] cache of the offset (in bytes) for the
+ *			   timestamp in the scan buffer
  * @available_scan_masks: [DRIVER] optional array of allowed bitmasks. Sort the
  *			   array in order of preference, the most preferred
  *			   masks first.
@@ -610,6 +612,7 @@ struct iio_dev {
 
 	struct iio_buffer		*buffer;
 	int				scan_bytes;
+	unsigned int			__private scan_timestamp_offset;
 
 	const unsigned long		*available_scan_masks;
 	unsigned int			__private masklength;

-- 
2.43.0