On many Macbooks since mid 2007, the Pro, C2D and Air models, applesmc
fails to read some or all SMC ports.  This problem has various effects,
such as flooded logfiles, malfunctioning temperature sensors,
accelerometers failing to initialize, and difficulties getting backlight
functionality to work properly.

The root of the problem seems to be the command protocol.  The current
code sends out a command byte, then repeatedly polls for an ack before
continuing to send or recieve data.  From experiments leading to this
patch, it seems the command protocol never quite worked or changed so that
one now sends a command byte, waits a little bit, polls for an ack, and if
it fails, repeats the whole thing by sending the command byte again.

This patch implements a send_command function according to the new
interpretation of the protocol, and should work also for earlier models.

Signed-off-by: Henrik Rydberg <rydberg@euromail.se>
Cc: Nicolas Boichat <nicolas@boichat.ch>
Cc: Riki Oktarianto <rkoktarianto@gmail.com>
Cc: Mark M. Hoffman <mhoffman@lightlink.com>
Cc: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>