hammer: Detect backlight circuitry
Pull-down means backlight is present, pull-up means backlight
is absent.
After detection, we still apply internal pull-down on the GPIO,
to make sure old boards with both pull-up and pull-down stuffed
do not always keep backlight on.
BRANCH=none
BUG=b:67722756
TEST=On reworked board with pull-down on backlight pin,
backlight works, and "Backlight present" shown in console.
TEST=On old board with both pull-up and pull-down, backlight is
off by default, and "Backlight not present" shown in console.
Change-Id: I6988c6ef8f4d155a08967db34f72d7ea4c835306
Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/538458
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>
3 files changed
