[PATCH v3 1/6] tools: iio: iio_generic_buffer ensure alignment

[Matti Vaittinen <mazziesaccount@gmail.com>]

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The iio_generic_buffer can return garbage values when the total size of
scan data is not a multiple of 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 elemnt is first in the buffer.

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

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

Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
---
Please note, This one could have RFC in subject.:
I attempted to write the fix so that the alignment is done based on the
biggest channel data. This may be wrong. Maybe a fixed 8 byte alignment
should be used instead? This patch can be dropped from the series if the
fix is not correct / agreed.

 tools/iio/iio_generic_buffer.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/tools/iio/iio_generic_buffer.c b/tools/iio/iio_generic_buffer.c
index 44bbf80f0cfd..fc562799a109 100644
--- 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 +69,16 @@ static unsigned int size_from_channelarray(struct iio_channel_info *channels, in
 		bytes = channels[i].location + channels[i].bytes;
 		i++;
 	}
+	/*
+	 * We wan't the data in next sample to also be properly aligned so
+	 * we'll add padding at the end if needed. TODO: should we use fixed
+	 * 8 byte alignment instead of the size of the biggest samnple?
+	 */
+	misalignment = bytes % max;
+	if (misalignment) {
+		printf("Misalignment %u. Adding Padding %u\n", misalignment,  max - misalignment);
+		bytes += max - misalignment;
+	}
 
 	return bytes;
 }
-- 
2.41.0


-- 
Matti Vaittinen, Linux device drivers
ROHM Semiconductors, Finland SWDC
Kiviharjunlenkki 1E
90220 OULU
FINLAND

~~~ "I don't think so," said Rene Descartes. Just then he vanished ~~~
Simon says - in Latin please.
~~~ "non cogito me" dixit Rene Descarte, deinde evanescavit ~~~
Thanks to Simon Glass for the translation =] 

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