[PATCH RFC 0/2] input: driver for RPi's official 7" touchscreen

[Nicolas Saenz Julienne]

This small series adds support for Raspberry pi's 7" touchscreen. Which
alongside with the backlight driver are the last devices needed to have
a functional touchscreen upstream.

With this setup the board's VC4 firmware takes care of communicating
with the touch chip and provides data though a shared memory area
provided by the driver. The driver takes care of polling the firmware
whenever at around 60Hz since there is no interrupt line available.

The 1.0 revision of the touchscreen is based on the ft5426 chip.
Technically, with some changes in edt-ft54x4.c we should be able to
access the data directly through I2C. Yet this bus is meant to be owned
by RPi's firmware and might access it anytime. For example, to
configure RPi's camera device. As sharing the bus master interface is
not possible a series of alternatives have been tested unsuccessfully
[1]. It seems that we'll be unable to access the chip directly in a
"clean" way which leaves us with this firmware based solution.

The driver was rewritten based on the one available on the downstream
Raspberry Pi kernel tree: https://github.com/raspberrypi/linux/.

This series is based on v4.20-rc5 and was tested on a RPi 3 B+.

[1] https://lists.infradead.org/pipermail/linux-rpi-kernel/2018-December/008444.html
===

Nicolas Saenz Julienne (2):
  input: add official Raspberry Pi's 7" touchscreen driver
  Input: raspberrypi-ts - add devicetree binding documentation

 .../touchscreen/raspberrypi,firmware-ts.txt   |  25 ++
 drivers/input/touchscreen/Kconfig             |  12 +
 drivers/input/touchscreen/Makefile            |   1 +
 drivers/input/touchscreen/raspberrypi-ts.c    | 252 ++++++++++++++++++
 4 files changed, 290 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/input/touchscreen/raspberrypi,firmware-ts.txt
 create mode 100644 drivers/input/touchscreen/raspberrypi-ts.c

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2.19.2