Re: [RFC PATCH 0/3] Introduce IIO interface for fingerprint sensors

[Lars-Peter Clausen]

Adding V4L folks to Cc for more input.

On 12/08/2014 03:10 PM, Baluta, Teodora wrote:
> Hello,
>
> 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 [0].
> > >
> > > 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 [0]). So, the IIO framework would support a uniform way of handling
> fingerprint devices that either do processing in software or in
> hardware.
>
> 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.
>
> Thanks,
> Teodora
>
> [0] http://www.freedesktop.org/wiki/Software/fprint/libfprint/upekts/
>
>
> > > 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.
> > >
> > > [0] 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
>
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