iio: exynos-adc: add experimental touchscreen support

This adds support for the touchscreen on Samsung s3c64xx.
The driver is completely untested but shows roughly how
it could be done, following the example of the at91 driver.

Open questions include:

- compared to the old plat-samsung/adc driver, there is
  no support for prioritizing ts over other clients, nor
  for oversampling. From my reading of the code, the
  priorities didn't actually have any effect at all, but
  the oversampling might be needed. Maybe the original
  authors have some insight.

- We probably need to add support for platform_data as well,
  I've skipped this so far.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
2 files changed