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

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Date:	Mon, 8 Dec 2014 14:10:41 +0000
From:	"Baluta, Teodora" <teodora.baluta@...el.com>
To:	"jic23@...nel.org" <jic23@...nel.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>
Subject: Re: [RFC PATCH 0/3] Introduce IIO interface for fingerprint sensors

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
> > 
>