On Mon, 25 Sep 2023 12:50:46 +0300
Matti Vaittinen <mazziesaccount@xxxxxxxxx> wrote:
> On 9/24/23 18:59, Jonathan Cameron wrote:
> > On Fri, 22 Sep 2023 14:16:57 +0300
> > Matti Vaittinen <mazziesaccount@xxxxxxxxx> wrote:
> >
> >> The available_scan_mask is an array of bitmaps representing the channels
> >> which can be simultaneously enabled by the driver. In many cases the
> >> hardware can offer more channels than what the user is interested in
> >> obtaining. In such cases it may be preferred that only subset of
> >> channels are enabled, and driver reads only a subset of the channels from
> >> the hardware.
> >>
> >> Some devices can't support all channel combinations. For example the
> >> BM1390 pressure sensor must always read the pressure data in order to
> >> acknowledge the watermark IRQ, while reading temperature can be omitted.
> >> So, the available scan mask would be 'pressure and temperature' and
> >> 'pressure only'.
> >>
> >> When IIO seatchs for the scan mask it asks the driver to use, it will
> >
> > Spell check description. searches
>
> Oh, right. Thanks!
>
> >
> >> pick the first suitable one from the 'available_scan_mask' array. Hence,
> >> ordering the masks in the array makes difference. We should 'prefer'
> >> reading just the pressure from the hardware (as it is cheaper operation
> >> than reading both pressure and temperature) over reading both pressure
> >> and temperature. Hence, we should set the 'only pressure' as first scan
> >> mask in available_scan_mask array. If we set the 'pressure and
> >> temperature' as first in array, then the 'only temperature' will never
> >> get used as 'pressure and temperature' can always serve the user's
> >> needs.
> >>
> >> Add (minimal) kerneldoc to the 'available_scan_mask' to hint the user
> >> that ordering of masks matters.
> >>
> >> Signed-off-by: Matti Vaittinen <mazziesaccount@xxxxxxxxx>
> >> ---
> >> include/linux/iio/iio.h | 4 +++-
> >> 1 file changed, 3 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
> >> index 202e55b0a28b..7bfa1b9bc8a2 100644
> >> --- a/include/linux/iio/iio.h
> >> +++ b/include/linux/iio/iio.h
> >> @@ -556,7 +556,9 @@ struct iio_buffer_setup_ops {
> >> * and owner
> >> * @buffer: [DRIVER] any buffer present
> >> * @scan_bytes: [INTERN] num bytes captured to be fed to buffer demux
> >> - * @available_scan_masks: [DRIVER] optional array of allowed bitmasks
> >> + * @available_scan_masks: [DRIVER] optional array of allowed bitmasks. Sort the
> >> + * array in order of preference, the most preferred
> >> + * masks first.
> >
> > LGTM
>
> I'll try to spell check the commit message and then I treat this as an
> ack. Please, let me know if it's not Ok.
Given I'll be picking these up anyway, not a formal Ack that you should carry
with the next version, but looks fine to me.
J
>
> >> * @masklength: [INTERN] the length of the mask established from
> >> * channels
> >> * @active_scan_mask: [INTERN] union of all scan masks requested by buffers
> >
>
