Re: [PATCH v2 00/10] Add support for SAMA5D2 touchscreen

[Quentin Schulz <quentin.schulz@bootlin.com>]

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Hi Jonathan and Eugen,

On Fri, Mar 30, 2018 at 02:02:12PM +0100, Jonathan Cameron wrote:
> On Tue, 27 Mar 2018 15:32:33 +0300
> Eugen Hristev <eugen.hristev@microchip.com> wrote:
> 
> > Hello,
> > 
> > This patch series is a rework of my previous series named:
> > [PATCH 00/14] iio: triggers: add consumer support
> > 
> > In few words, this is the implementation of splitting the functionality
> > of the IP block ADC device in SAMA5D2 SoC from ADC with touchscreen
> > support. In order to avoid having a MFD device, two separate
> > drivers that would work on same register base and split the IRQ,etc,
> > as advised on the mailing list, I created a consumer driver for the
> > channels, that will connect to the ADC as described in the device tree.
> > 
> > I have collected feedback from everyone and here is the result:
> > I have added a new generic resistive touchscreen driver, which acts
> > as a iio consumer for the given channels and will create an input
> > device and report the events. It uses a callback buffer to register
> > to the IIO device and waits for data to be pushed.
> > Inside the IIO device, I have kept a similar approach with the first version
> > of the series, except that now the driver can take multiple buffers, and
> > will configure the touchscreen part of the hardware device if the specific
> > channels are requested.
> > 
> > The SAMA5D2 ADC driver registers three new channels: two for the
> > position on the X and Y axis, and one for the touch pressure.
> > When channels are requested, it will check if the touchscreen channel mask
> > includes the requested channels (it is possible that the consumer driver
> > will not request pressure for example). If it's the case, it will work
> > in touchscreen mode, and will refuse to do usual analog-digital conversion,
> > because we have a single trigger and the touchscreen needs it.
> > When the scan mask will include only old channels, the driver will function
> > in the same way as before. If the scan mask somehow is a mix of the two (the
> > masks intersect), the driver will refuse to work whatsoever (cannot have both
> > in the same time).
> > The driver allows reading raw data for the new channels, if claim direct
> > mode works: no touchscreen driver requested anything. The new channels can
> > act like the old ones. However, when requesting these channels, the usual
> > trigger will not work and will not be enabled. The touchscreen channels
> > require special trigger and irq configuration: pen detect, no pen detect
> > and a periodic trigger to sample the touchscreen position and pressure.
> > If the user attempts to use another trigger while there is a buffer
> > that already requested the touchscreen channels (thus the trigger), the
> > driver will refuse to comply.
> > 
> > In order to have defines for the channel numbers, I added a bindings include
> > file that goes on a separate commit :
> > dt-bindings: iio: adc: at91-sama5d2_adc: add channel specific consumer info
> > This should go in the same tree with the following commits :
> >   ARM: dts: at91: sama5d2: add channel cells for ADC device
> >   ARM: dts: at91: sama5d2: Add resistive touch device
> > 
> > as build will break because these commits depend on the binding one
> > which creates the included header file.
> > 
> > After the discussions earlier this year on the mailing list, I hope this
> > rework of the patches is much better and fulfills all the requirements
> > for this implementation.
> As I said in one of the later patches, I like this a lot.
> It is a good blend of the moderately nasty handling needed in the ADC
> driver with a lovely generic input driver.
> 
> Very nice!  Hope everyone else agrees ;)
> 

I'd love to see a generic touchscreen driver being an iio consumer!

However, I've already a case that can't be handled unfortunately.

I posted ~2 years ago a patch series[1] for touchscreen support for
Allwinner SoCs that are using their ADC (also) for touchscreen purpose.

It's been a very long time, I'm trying the hardest I can with my
"IIRC-skills".

There are several problems:
  - Data is stored in one register as a queue following this scheme:
    X @t=0 coord, Y @t=0 coord, X @t=1 coord, Y @t=1 coord, X @t=2
    coord, Y @t=2 coord, etc...

    Thus, I suppose I've only one channel and not two for coordinates.

  - The first data stored after an up event is absolutely unreliable so
  I have to flush it, thus I need to use another API call to have the
  touchscreen driver do some logic with a whole queue only when it's
  after an up event (it doesn't really make sense to do so in the IIO
  driver, does it?).

  - This up event is an interrupt.. that is configurable from the same
  set of registers than for the ADC, so I need an mfd,

What are your thoughts (and maybe workarounds?) on those issues?

Thanks,
Quentin

[1] https://lkml.org/lkml/2016/7/20/156

> Jonathan
> 
> > 
> > Eugen Hristev (10):
> >   MAINTAINERS: add generic resistive touchscreen adc
> >   iio: Add channel for Position Relative
> >   dt-bindings: input: touchscreen: touch_adc: create bindings
> >   iio: inkern: add module put/get on iio dev module when requesting
> >     channels
> >   iio: adc: at91-sama5d2_adc: fix channel configuration for differential
> >     channels
> >   iio: adc: at91-sama5d2_adc: add support for position and pressure
> >     channels
> >   input: touchscreen: touch_adc: add generic resistive ADC touchscreen
> >   dt-bindings: iio: adc: at91-sama5d2_adc: add channel specific consumer
> >     info
> >   ARM: dts: at91: sama5d2: add channel cells for ADC device
> >   ARM: dts: at91: sama5d2: Add resistive touch device
> > 
> >  Documentation/ABI/testing/sysfs-bus-iio            |  12 +
> >  .../bindings/iio/adc/at91-sama5d2_adc.txt          |   9 +
> >  .../bindings/input/touchscreen/touch_adc.txt       |  33 ++
> >  MAINTAINERS                                        |   6 +
> >  arch/arm/boot/dts/sama5d2.dtsi                     |  12 +
> >  drivers/iio/adc/at91-sama5d2_adc.c                 | 491 ++++++++++++++++++++-
> >  drivers/iio/industrialio-core.c                    |   1 +
> >  drivers/iio/inkern.c                               |   8 +-
> >  drivers/input/touchscreen/Kconfig                  |  13 +
> >  drivers/input/touchscreen/Makefile                 |   1 +
> >  drivers/input/touchscreen/touch_adc.c              | 199 +++++++++
> >  include/dt-bindings/iio/adc/at91-sama5d2_adc.h     |  16 +
> >  include/uapi/linux/iio/types.h                     |   1 +
> >  tools/iio/iio_event_monitor.c                      |   2 +
> >  14 files changed, 791 insertions(+), 13 deletions(-)
> >  create mode 100644 Documentation/devicetree/bindings/input/touchscreen/touch_adc.txt
> >  create mode 100644 drivers/input/touchscreen/touch_adc.c
> >  create mode 100644 include/dt-bindings/iio/adc/at91-sama5d2_adc.h
> > 
> 
> 
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