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.
* @masklength: [INTERN] the length of the mask established from
* channels
* @active_scan_mask: [INTERN] union of all scan masks requested by buffers
--
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland
~~ When things go utterly wrong vim users can always type :help! ~~
