> -----Original Message----- > From: Jonathan Cameron [mailto:jic23@xxxxxxxxxx] > Sent: 18 April, 2015 19:47 > To: Tirdea, Irina; linux-iio@xxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx > Cc: linux-kernel@xxxxxxxxxxxxxxx; Hartmut Knaack; Lars-Peter Clausen; Peter Meerwald; Rob Herring; Pawel Moll; Mark Rutland; Ian > Campbell; Kumar Gala > Subject: Re: [PATCH 1/3] iio: core: Introduce IIO_CHAN_INFO_CALIBREPETITIONS > > On 17/04/15 11:50, Irina Tirdea wrote: > > Some magnetometers can perform a number of repetitions in HW > > for each measurement to increase accuracy. One example is > > Bosch BMC150: > > http://ae-bst.resource.bosch.com/media/products/dokumente/bmc150/BST-BMC150-DS000-04.pdf. > > > > Introduce an interface to set the number of repetitions > > for these devices. > > > > Signed-off-by: Irina Tirdea <irina.tirdea@xxxxxxxxx> > > --- > > Documentation/ABI/testing/sysfs-bus-iio | 10 ++++++++++ > > drivers/iio/industrialio-core.c | 1 + > > include/linux/iio/iio.h | 1 + > > 3 files changed, 12 insertions(+) > > > > diff --git a/Documentation/ABI/testing/sysfs-bus-iio b/Documentation/ABI/testing/sysfs-bus-iio > > index 866b4ec..74c1444 100644 > > --- a/Documentation/ABI/testing/sysfs-bus-iio > > +++ b/Documentation/ABI/testing/sysfs-bus-iio > > @@ -1375,3 +1375,13 @@ Description: > > The emissivity ratio of the surface in the field of view of the > > contactless temperature sensor. Emissivity varies from 0 to 1, > > with 1 being the emissivity of a black body. > > + > > +What: /sys/bus/iio/devices/iio:deviceX/in_magn_x_calibrepetitions > > +What: /sys/bus/iio/devices/iio:deviceX/in_magn_y_calibrepetitions > > +What: /sys/bus/iio/devices/iio:deviceX/in_magn_z_calibrepetitions > > +KernelVersion: 4.2 > > +Contact: linux-iio@xxxxxxxxxxxxxxx > > +Description: > > + Hardware applied number of repetitions for acquiring one > > + data point. The HW will do <type>[_name]_calibrepetitions > > + measurements and return the average value as output data. > This is an interesting way of naming what is often referred to as oversampling. > I'd like to get some other opinions on naming before we go with the ABI for this.. > > We do have one driver in staging exporting oversampling_ratio which is probably > the same thing, but that ABI was never standardized so I have no problem with > ignoring that one case. A couple of other drivers provide oversampling control > via platform data. We must make sure we give a sensible default for this. > I didn't know about the oversampling_ratio. I used "repetitions" because Bosch calls them so in the datasheet. However, I think oversampling_ratio is a better name since it suggests a connection with sampling. I will change it to oversampling_ratio in v2 and then wait for more opinions on this. > There is also the interesting question of whether sampling_frequency applies > before or after this... I'd argue after, but again would like more opinions > before we dictate that. However, whatever we choose should definitely be > documented here! > The HW sees the sampling_frequency as the frequency the user sees, so it does not take into account the oversampling_ratio: each value resulted after oversampling_ratio repetitions is considered one sample for the sampling_frequency. However, I am not sure how other devices handle this so more opinions on this would be useful. Looking more into the oversampling ratio from BMC150, seems there are some sampling limitations I missed the first time: when setting a certain value for x/y/z repetitions, not all sampling rates are available. I am going to fix this in v2 by not allowing invalid sampling rates once a certain value for oversampling_ratio is set. Thanks, Irina > > diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c > > index 7c98bc1..9e0da7f 100644 > > --- a/drivers/iio/industrialio-core.c > > +++ b/drivers/iio/industrialio-core.c > > @@ -129,6 +129,7 @@ static const char * const iio_chan_info_postfix[] = { > > [IIO_CHAN_INFO_DEBOUNCE_COUNT] = "debounce_count", > > [IIO_CHAN_INFO_DEBOUNCE_TIME] = "debounce_time", > > [IIO_CHAN_INFO_CALIBEMISSIVITY] = "calibemissivity", > > + [IIO_CHAN_INFO_CALIBREPETITIONS] = "calibrepetitions", > > }; > > > > /** > > diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h > > index b1e46ae..07fbfb2 100644 > > --- a/include/linux/iio/iio.h > > +++ b/include/linux/iio/iio.h > > @@ -44,6 +44,7 @@ enum iio_chan_info_enum { > > IIO_CHAN_INFO_DEBOUNCE_COUNT, > > IIO_CHAN_INFO_DEBOUNCE_TIME, > > IIO_CHAN_INFO_CALIBEMISSIVITY, > > + IIO_CHAN_INFO_CALIBREPETITIONS, > > }; > > > > enum iio_shared_by { > > -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
