On Mon, 31 Aug 2020 20:00:43 -0700 Gwendal Grignou <gwendal@xxxxxxxxxxxx> wrote: > On Sun, Aug 30, 2020 at 6:11 AM Jonathan Cameron <jic23@xxxxxxxxxx> wrote: > > > > On Fri, 28 Aug 2020 16:31:56 -0700 > > Gwendal Grignou <gwendal@xxxxxxxxxxxx> wrote: > > > > > Some sensors/sensorhubs can calculate drift or hard iron offsets to > > > apply to raw data to get the true measure data. > > > These offsets are applied by the user space application. > > > When these offsets change, events are raised to tell the application > > > to update the cached offset values. > > > > > > Signed-off-by: Gwendal Grignou <gwendal@xxxxxxxxxxxx> > > Hi Gwendal > > > > This strikes me as rather prone to races. I guess if the updates > > tend to be fairly minor we will just have slightly less accurate data > > until the update gets picked up by userspace. > In case of hard iron for instance, the sensorhub needs several samples > to find out the current offset are now invalid. So it is likely the > measurement of the geomagnetic field was incorrect for a while. > For accelerometer online calibration, we don't expect vast changes > when new offsets are available. > > > > We have had some discussions about how to handle meta data updates > > in the past. One option was to provide a metadata index channel > > that could be used to indicate there was an update to something > > sat in a separate fifo. > An extra sounds like a waste of space, as it will mostly be 0 most of > the time, and edge to 1 once in a while. An event looks more > appropriate. Agreed for this case. It would be a much more general interface with a lot of other usecases. It is overkill here. There isn't a huge burden in adding support for your case in the meantime, even if we eventually end up finding a better way of doing metadata in general. > > > > > --- > > > Documentation/ABI/testing/sysfs-bus-iio | 33 +++++++++++++++++++++++++ > > > 1 file changed, 33 insertions(+) > > > > > > diff --git a/Documentation/ABI/testing/sysfs-bus-iio b/Documentation/ABI/testing/sysfs-bus-iio > > > index 47df16c87862d..40da602e7a555 100644 > > > --- a/Documentation/ABI/testing/sysfs-bus-iio > > > +++ b/Documentation/ABI/testing/sysfs-bus-iio > > > @@ -1716,3 +1716,36 @@ Description: > > > Mass concentration reading of particulate matter in ug / m3. > > > pmX consists of particles with aerodynamic diameter less or > > > equal to X micrometers. > > > + > > > +What: /sys/bus/iio/devices/iio:deviceX/in_anglvel_x_offset > > > +What: /sys/bus/iio/devices/iio:deviceX/in_anglvel_y_offset > > > +What: /sys/bus/iio/devices/iio:deviceX/in_anglvel_z_offset > > > +KernelVersion: x.y > > > +Contact: linux-iio@xxxxxxxxxxxxxxx > > > +Description: > > > + Gyroscope drift calculated by the sensor. In addition to factory > > > + calibration, sensor or sensorhub can > > > + detect gyroscope drift and report it to userspace. > > > > This looks like standard ABI that should probably already be documented, > > unrelated to the controversial part of this patch. I would split it out into > > it's own patch a I can pick that up much faster. > Done in v2. > > > > > > > + > > > +What: /sys/bus/iio/devices/iio:deviceX/in_magn_x_offset > > > +What: /sys/bus/iio/devices/iio:deviceX/in_magn_y_offset > > > +What: /sys/bus/iio/devices/iio:deviceX/in_magn_z_offset > > > +KernelVersion: x.y > > > +Contact: linux-iio@xxxxxxxxxxxxxxx > > > +Description: > > > + Hard Iron bias calculated by the sensor or sensorhub. To be applied by > > > + user space application to the raw data to obtain the geomagnetic field. > > > > Same as above. > Done in v2. > > > > > + > > > +What: /sys/.../iio:deviceX/events/in_accel_offset_change_en > > > +What: /sys/.../iio:deviceX/events/in_magn_offset_change_en > > > +What: /sys/.../iio:deviceX/events/in_magn_scale_change_en > > > +What: /sys/.../iio:deviceX/events/in_anglvel_offset_change_en > > > +KernelVersion: x.y > > > +Contact: linux-iio@xxxxxxxxxxxxxxx > > > +Description: > > > + Some sensors internally calculate offset to apply to remove bias (for > > > + instance, hard/soft-iron bias for magnetometer, online calibration bias for > > > + gyroscope or accelerometer). > > > + When the sensor computes a new set of offset values, it generates an > > > + event for the userspace application to refresh the offsets to apply to raw > > > + data. > > > > I'm not totally sold on this idea, though would like inputs from other people before > > ruling it out. > > > > One minor change I'd make would be to have a single event to indicate that something > > userspace might care about in the way of metadata for this channel has changed. > > I guess something like > Make sense, scale and offset should be checked together if they both exists. > Using vents/in_<type>_metadata_en in v2. > > > > in_accel_metachange_en etc with a single new event code. For events, it's the event > > code mapping that normally matters more than sysfs binding as that is much more > > tightly restricted. > > > > Jonathan > >
