On 9/24/23 18:57, Jonathan Cameron wrote:
On Fri, 22 Sep 2023 14:16:08 +0300
Matti Vaittinen <mazziesaccount@xxxxxxxxx> wrote:
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@xxxxxxxxx>
---
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?
+ */
Should be aligned to max size seen in the scan.
Or, maybe it should be
min(max_size_in_scan, 8);
?
I think my suggestion above may yield undesirable effects should the
scan elements be greater than 8 bytes. (Don't know if this is supported
though)
+ misalignment = bytes % max;
+ if (misalignment) {
+ printf("Misalignment %u. Adding Padding %u\n", misalignment, max - misalignment);
No print statement as this is correct behaviour (well the tool is buggy but the kernel generates it
correctly I believe). Fine to add a comment though!
Oh, indeed. The print was forgotten from my test runs. Thanks for
pointing it out!
+ bytes += max - misalignment;
+ }
return bytes;
}
Yours,
-- Matti
--
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland
~~ When things go utterly wrong vim users can always type :help! ~~
