Re: [RFC PATCH 0/3] Introduce IIO interface for fingerprint sensors
From: Baluta, Teodora
Date: Mon Dec 08 2014 - 09:26:47 EST
On Vi, 2014-12-05 at 02:15 +0000, Jonathan Cameron wrote:
> On 04/12/14 13:00, Teodora Baluta wrote:
> > This patchset adds support for fingerprint sensors through the IIO interface.
> > This way userspace applications collect information in a uniform way. All
> > processing would be done in the upper layers as suggested in .
> > In order to test out this proposal, a minimal implementation for UPEK's
> > TouchChip Fingerprint Sensor via USB is also available. Although there is an
> > existing implementation in userspace for USB fingerprint devices, including this
> > particular device, the driver represents a proof of concept of how fingerprint
> > sensors could be integrated in the IIO framework regardless of the used bus. For
> > lower power requirements, the SPI bus is preferred and a kernel driver
> > implementation makes more sense.
> So why not v4l? These are effectively image sensors..
Well, here's why I don't think v4l would be the best option:
- an image scanner could be implemented in the v4l subsystem, but it
seems far more complicated for a simple fingerprint scanner - it usually
has drivers for webcams, TVs or video streaming devices. The v4l
subsystem (with all its support for colorspace, decoders, image
compression, frame control) seems a bit of an overkill for a very
straightforward fingerprint imaging sensor.
- a fingerprint device could also send out a processed information, not
just the image of a fingerprint. This means that the processing is done
in hardware - the UPEK TouchStrip chipset in libfprint has this behavior
(see ). So, the IIO framework would support a uniform way of handling
fingerprint devices that either do processing in software or in
The way I see it now, for processed fingerprint information, an IIO
device could have an IIO_FINGERPRINT channel with a modifier and only
the sensitivity threshold attribute set. We would also need two
triggers: one for enrollment and one for the verification mode to
control the device from a userspace application.
> > A sysfs trigger is enabled and the device starts scanning. As soon as an image
> > is available it is written in the character device /dev/iio:deviceX.
> > Userspace applications will be able to calculate the expected image size using
> > the fingerprint attributes height, width and bit depth. Other attributes
> > introduced for the fingerprint channel in IIO represent information that aids in
> > the fingerprint image processing. Besides these, the proposed interface offers
> > userspace a way to read a feedback after a scan (like the swipe was too slow or
> > too fast) through a modified fingerprint_status channel.
> >  http://www.spinics.net/lists/linux-iio/msg11463.html
> > Teodora Baluta (3):
> > iio: core: add support for fingerprint devices
> > iio: core: change channel's storagebits/realbits to u32
> > iio: fingerprint: add fingerprint sensor via USB
> > Documentation/ABI/testing/sysfs-bus-iio | 51 +++
> > drivers/iio/Kconfig | 1 +
> > drivers/iio/Makefile | 1 +
> > drivers/iio/fingerprint/Kconfig | 15 +
> > drivers/iio/fingerprint/Makefile | 5 +
> > drivers/iio/fingerprint/fp_tc.c | 162 +++++++++
> > drivers/iio/fingerprint/fp_tc.h | 22 ++
> > drivers/iio/fingerprint/fp_tc_usb.c | 618 ++++++++++++++++++++++++++++++++
> > drivers/iio/fingerprint/fp_tc_usb.h | 144 ++++++++
> > drivers/iio/industrialio-core.c | 9 +
> > include/linux/iio/iio.h | 11 +-
> > include/linux/iio/types.h | 10 +
> > 12 files changed, 1047 insertions(+), 2 deletions(-)
> > create mode 100644 drivers/iio/fingerprint/Kconfig
> > create mode 100644 drivers/iio/fingerprint/Makefile
> > create mode 100644 drivers/iio/fingerprint/fp_tc.c
> > create mode 100644 drivers/iio/fingerprint/fp_tc.h
> > create mode 100644 drivers/iio/fingerprint/fp_tc_usb.c
> > create mode 100644 drivers/iio/fingerprint/fp_tc_usb.h