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 <[email protected]>
Fixes: e58537ccce73 ("staging: iio: update example application.")
---
Revision history
v4 => v5:
- drop unnecessary comment.
- drop all other patches as those were already applied.
- add Fixes-tag.
v3 => v4:
- drop extra print and TODO coment
- add comment clarifying alignment sizes
---
tools/iio/iio_generic_buffer.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/tools/iio/iio_generic_buffer.c b/tools/iio/iio_generic_buffer.c
index 44bbf80f0cfd..c1c037ee0071 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 +69,14 @@ 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. Adding padding only
+ * works for channel data which size is 2^n bytes.
+ */
+ misalignment = bytes % max;
+ if (misalignment)
+ bytes += max - misalignment;
return bytes;
}
base-commit: 0bb80ecc33a8fb5a682236443c1e740d5c917d1d
--
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 =]
On 10/2/23 15:54, Matti Vaittinen wrote:
> 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 <[email protected]>
> Fixes: e58537ccce73 ("staging: iio: update example application.")
>
> ---
> Revision history
> v4 => v5:
> - drop unnecessary comment.
> - drop all other patches as those were already applied.
> - add Fixes-tag.
> v3 => v4:
> - drop extra print and TODO coment
> - add comment clarifying alignment sizes
> ---
> tools/iio/iio_generic_buffer.c | 13 ++++++++++++-
> 1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/tools/iio/iio_generic_buffer.c b/tools/iio/iio_generic_buffer.c
> index 44bbf80f0cfd..c1c037ee0071 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 +69,14 @@ 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
I just realized I didn't fix the typo mentioned by Andy. I can re-spin
this with wan't => want. Sorry!
> + * 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;
> }
>
> base-commit: 0bb80ecc33a8fb5a682236443c1e740d5c917d1d
--
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland
~~ When things go utterly wrong vim users can always type :help! ~~