This patch optimizes the gpio data register handling for gpio_set_value().
Instead of using the good old spinlock-plus-read-modify-write strategy
we now use a shadow register and atomic operations.
This improves the bitbanging mmc performance on Migo-R from 26 Kbytes/s
to 40 Kbytes/s.
Signed-off-by: Magnus Damm <damm@igel.co.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>