| Message ID | ZRq9lm/C7g9m9zen@dc78bmyyyyyyyyyyyyydt-3.rev.dnainternet.fi (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v5] tools: iio: iio_generic_buffer ensure alignment | expand |
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 <mazziesaccount@gmail.com> > 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
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; }
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.") --- 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(-) base-commit: 0bb80ecc33a8fb5a682236443c1e740d5c917d1d