Patch "tools: iio: iio_generic_buffer ensure alignment" has been added to the 4.19-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    tools: iio: iio_generic_buffer ensure alignment

to the 4.19-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     tools-iio-iio_generic_buffer-ensure-alignment.patch
and it can be found in the queue-4.19 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 84ac110377c692c44cd40fbea59f95e896db653d
Author: Matti Vaittinen <mazziesaccount@xxxxxxxxx>
Date:   Tue Oct 3 12:57:47 2023 +0300

    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@xxxxxxxxx>
    Fixes: e58537ccce73 ("staging: iio: update example application.")
    Link: https://lore.kernel.org/r/ZRvlm4ktNLu+qmlf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
    Signed-off-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/tools/iio/iio_generic_buffer.c b/tools/iio/iio_generic_buffer.c
index 8360605f01db8..ca9f33fa51c9f 100644
--- a/tools/iio/iio_generic_buffer.c
+++ b/tools/iio/iio_generic_buffer.c
@@ -56,9 +56,12 @@ 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
@@ -68,6 +71,14 @@ 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;
 }