| Message ID | 20191202142714.12030-1-lars.moellendorf@plating.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | iio: buffer: align the size of scan bytes to size of the largest element | expand |
On Mon, 2 Dec 2019 15:27:14 +0100 Lars Möllendorf <lars.moellendorf@plating.de> wrote: Even when fixing a patch send issue as you did here, please mark clearly with v2 and add a change log saying that's what you did. Also please don't send in reply to the earlier thread, but instead as a completely new thread. The reply to thread thing seems sensible for simple cases, but when we get to v20 (it happens ;) things get really confusing :) > Previous versions of `iio_compute_scan_bytes` only aligned the current > element to its own length (i.e. its own natural alignment). This worked > in case the length of each channel's scan elements had been smaller then > the length of the successive channel's scan elements. I'd modify this description a little bit. The key thing was the length of the last element - didn't matter what happened before that. u32 u16 u32 would be aligned correctly I hope? > > E.g. > > u16 > u32 <- aligned to its natural alignment > > But if the length of a channel's scan elements is greater then the > length of scan elements of the consecutive channel no alignment had > been taken into account. This is however needed to preserve the > alignment for multiple consecutive sets of scan elements. > > u32 <- alignment is off by two byte for the second set of scan elements > u16 <- no alignment takes place > > This commit fixes this by aligning the scan bytes to the size of the > largest scan element. > > Signed-off-by: Lars Möllendorf <lars.moellendorf@plating.de> Code looks good to me, so just a v3 tidying up the message. Thanks for sorting this out! Ideally we'd add a specific fixes tag as well for when this was introduced but I fear it goes back nearly all the way (at least before the move out of staging) so we can probably leave that vague for this one unless you fancy some archaeology. Jonathan > --- > drivers/iio/industrialio-buffer.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c > index 5d05c38c4ba9..2f037cd59d53 100644 > --- a/drivers/iio/industrialio-buffer.c > +++ b/drivers/iio/industrialio-buffer.c > @@ -546,7 +546,7 @@ static int iio_compute_scan_bytes(struct iio_dev *indio_dev, > const unsigned long *mask, bool timestamp) > { > unsigned bytes = 0; > - int length, i; > + int length, i, largest = 0; > > /* How much space will the demuxed element take? */ > for_each_set_bit(i, mask, > @@ -554,13 +554,17 @@ static int iio_compute_scan_bytes(struct iio_dev *indio_dev, > length = iio_storage_bytes_for_si(indio_dev, i); > bytes = ALIGN(bytes, length); > bytes += length; > + largest = max(largest, length); > } > > if (timestamp) { > length = iio_storage_bytes_for_timestamp(indio_dev); > bytes = ALIGN(bytes, length); > bytes += length; > + largest = max(largest, length); > } > + > + bytes = ALIGN(bytes, largest); > return bytes; > } >
diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c index 5d05c38c4ba9..2f037cd59d53 100644 --- a/drivers/iio/industrialio-buffer.c +++ b/drivers/iio/industrialio-buffer.c @@ -546,7 +546,7 @@ static int iio_compute_scan_bytes(struct iio_dev *indio_dev, const unsigned long *mask, bool timestamp) { unsigned bytes = 0; - int length, i; + int length, i, largest = 0; /* How much space will the demuxed element take? */ for_each_set_bit(i, mask, @@ -554,13 +554,17 @@ static int iio_compute_scan_bytes(struct iio_dev *indio_dev, length = iio_storage_bytes_for_si(indio_dev, i); bytes = ALIGN(bytes, length); bytes += length; + largest = max(largest, length); } if (timestamp) { length = iio_storage_bytes_for_timestamp(indio_dev); bytes = ALIGN(bytes, length); bytes += length; + largest = max(largest, length); } + + bytes = ALIGN(bytes, largest); return bytes; }
Previous versions of `iio_compute_scan_bytes` only aligned the current element to its own length (i.e. its own natural alignment). This worked in case the length of each channel's scan elements had been smaller then the length of the successive channel's scan elements. E.g. u16 u32 <- aligned to its natural alignment But if the length of a channel's scan elements is greater then the length of scan elements of the consecutive channel no alignment had been taken into account. This is however needed to preserve the alignment for multiple consecutive sets of scan elements. u32 <- alignment is off by two byte for the second set of scan elements u16 <- no alignment takes place This commit fixes this by aligning the scan bytes to the size of the largest scan element. Signed-off-by: Lars Möllendorf <lars.moellendorf@plating.de> --- drivers/iio/industrialio-buffer.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)