tools: iio: iio_generic_buffer ensure alignment

[ Upstream commit 2d3dff577dd0ea8fe9637a13822f7603c4a881c8 ]

The iio_generic_buffer can return garbage values when the total size of
scan data is not a multiple of the largest element in the scan. This can be
demonstrated by reading a scan, consisting, for example of one 4-byte and
one 2-byte element, where the 4-byte element is first in the buffer.

The IIO generic buffer code does not take into account the last two
padding bytes that are needed to ensure that the 4-byte data for next
scan is correctly aligned.

Add the padding bytes required to align the next sample with the scan size.

Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Fixes: e58537ccce73 ("staging: iio: update example application.")
Link: https://lore.kernel.org/r/ZRvlm4ktNLu+qmlf@dc78bmyyyyyyyyyyyyydt-3.rev.dnainternet.fi
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/tools/iio/iio_generic_buffer.c b/tools/iio/iio_generic_buffer.c
index 44bbf80..0d0a7a1 100644 (file)
--- a/tools/iio/iio_generic_buffer.c
+++ b/tools/iio/iio_generic_buffer.c
@@ -54,9 +54,12 @@ enum autochan {
 static unsigned int size_from_channelarray(struct iio_channel_info *channels, int num_channels)
 {
        unsigned int bytes = 0;
-       int i = 0;
+       int i = 0, max = 0;
+       unsigned int misalignment;
 
        while (i < num_channels) {
+               if (channels[i].bytes > max)
+                       max = channels[i].bytes;
                if (bytes % channels[i].bytes == 0)
                        channels[i].location = bytes;
                else
@@ -66,6 +69,14 @@ static unsigned int size_from_channelarray(struct iio_channel_info *channels, in
                bytes = channels[i].location + channels[i].bytes;
                i++;
        }
+       /*
+        * We want the data in next sample to also be properly aligned so
+        * we'll add padding at the end if needed. Adding padding only
+        * works for channel data which size is 2^n bytes.
+        */
+       misalignment = bytes % max;
+       if (misalignment)
+               bytes += max - misalignment;
 
        return bytes;
 }