Implement selftest feature as specified by chip manufacturer.  Control:
read selftest sysfs entry

Response: "OK x y z" or "FAIL x y z"

where x, y, and z are difference between selftest mode and normal mode.
Test is passed when values are within acceptance limit values.

Acceptance limits are provided via platform data.  See chip spesifications
for acceptance limits.  If limits are not properly set, OK / FAIL decision
is meaningless.  However, userspace application can still make decision
based on the numeric x, y, z values.

Selftest is meant for HW diagnostic purposes.  It is not meant to be
called during normal use of the chip.  It may cause false interrupt
events.  Selftest mode delays polling of the normal results but it doesn't
cause wrong values.  Chip must be in static state during selftest.  Any
acceration during the test causes most probably failure.

Signed-off-by: Samu Onkalo <samu.p.onkalo@nokia.com>
Acked-by: Éric Piel <Eric.Piel@tremplin-utc.net>
Cc: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>