MFD: ucb1x00-core: fix gpiolib direction_output handling

gpiolib drivers should first set the output data before setting the
direction to avoid putting glitches on an output signal.  As an
additional bonus, we tweak the code to avoid unnecessary register
writes to the output and direction registers if they have no need
to be updated.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

diff --git a/drivers/mfd/ucb1x00-core.c b/drivers/mfd/ucb1x00-core.c
index 8ebda97981e1a31088bed973df65e45a1db5e6ab..febc90cdef7ea4a97885f7cc88b36ceb543e8b7e 100644 (file)
--- a/drivers/mfd/ucb1x00-core.c
+++ b/drivers/mfd/ucb1x00-core.c
@@ -148,16 +148,22 @@ static int ucb1x00_gpio_direction_output(struct gpio_chip *chip, unsigned offset
 {
        struct ucb1x00 *ucb = container_of(chip, struct ucb1x00, gpio);
        unsigned long flags;
+       unsigned old, mask = 1 << offset;
 
        spin_lock_irqsave(&ucb->io_lock, flags);
-       ucb->io_dir |= (1 << offset);
-       ucb1x00_reg_write(ucb, UCB_IO_DIR, ucb->io_dir);
-
+       old = ucb->io_out;
        if (value)
-               ucb->io_out |= 1 << offset;
+               ucb->io_out |= mask;
        else
-               ucb->io_out &= ~(1 << offset);
-       ucb1x00_reg_write(ucb, UCB_IO_DATA, ucb->io_out);
+               ucb->io_out &= ~mask;
+
+       if (old != ucb->io_out)
+               ucb1x00_reg_write(ucb, UCB_IO_DATA, ucb->io_out);
+
+       if (!(ucb->io_dir & mask)) {
+               ucb->io_dir |= mask;
+               ucb1x00_reg_write(ucb, UCB_IO_DIR, ucb->io_dir);
+       }
        spin_unlock_irqrestore(&ucb->io_lock, flags);
 
        return 0;