| Message ID | 4e43bf0186df5c8a56b470318b4827605f9cad6c.1695727471.git.mazziesaccount@gmail.com (mailing list archive) |
|---|---|
| State | Accepted |
| Headers | show |
| Series | Support ROHM BM1390 pressure sensor | expand |
On Wed, 27 Sep 2023 11:27:41 +0300 Matti Vaittinen <mazziesaccount@gmail.com> 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 a subset of > channels are enabled, and the 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 masks would be 'pressure and temperature' and > 'pressure only'. > > When IIO searches for the scan mask it asks the driver to use, it will > pick the first suitable one from the 'available_scan_mask' array. Hence, > ordering the masks in the array makes a difference. We should 'prefer' > reading just the pressure from the hardware (as it is a cheaper operation > than reading both pressure and temperature) over reading both pressure > and temperature. Hence, we should set the 'only pressure' as the first > scan mask in available_scan_mask array. If we set the 'pressure and > temperature' as first in the 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 the ordering of masks matters. > > Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com> Applied this patch to the togreg branch of iio.git If you fancy turning the patch description into some more formal documentation under Documentation/... that might be a good thing in the long run. I always mean to spend some time working on that, but too manyt things to do :( Thanks, Jonathan > --- > 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. > * @masklength: [INTERN] the length of the mask established from > * channels > * @active_scan_mask: [INTERN] union of all scan masks requested by buffers
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. * @masklength: [INTERN] the length of the mask established from * channels * @active_scan_mask: [INTERN] union of all scan masks requested by buffers
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 a subset of channels are enabled, and the 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 masks would be 'pressure and temperature' and 'pressure only'. When IIO searches for the scan mask it asks the driver to use, it will pick the first suitable one from the 'available_scan_mask' array. Hence, ordering the masks in the array makes a difference. We should 'prefer' reading just the pressure from the hardware (as it is a cheaper operation than reading both pressure and temperature) over reading both pressure and temperature. Hence, we should set the 'only pressure' as the first scan mask in available_scan_mask array. If we set the 'pressure and temperature' as first in the 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 the ordering of masks matters. Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com> --- include/linux/iio/iio.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)