gpio: syscon: add soc specific callback to assign output value

Some SoCs (like Keystone) may require to perform special
sequence of operations to assign output GPIO value, so default
implementation of .set() callback from gpio-syscon driver
can't be used.

Hence, add optional, SoC specific callback to assign output
gpio value.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-syscon.c

@@ -37,6 +37,8 @@
  * dat_bit_offset:	Offset (in bits) to the first GPIO bit.
  * dir_bit_offset:	Optional offset (in bits) to the first bit to switch
  *			GPIO direction (Used with GPIO_SYSCON_FEAT_DIR flag).
+ * set:		HW specific callback to assigns output value
+ *			for signal "offset"
  */
 
 struct syscon_gpio_data {
@@ -45,6 +47,8 @@ struct syscon_gpio_data {
 	unsigned int	bit_count;
 	unsigned int	dat_bit_offset;
 	unsigned int	dir_bit_offset;
+	void		(*set)(struct gpio_chip *chip,
+			       unsigned offset, int value);
 };
 
 struct syscon_gpio_priv {
@@ -111,7 +115,7 @@ static int syscon_gpio_dir_out(struct gpio_chip *chip, unsigned offset, int val)
 				   BIT(offs % SYSCON_REG_BITS));
 	}
 
-	syscon_gpio_set(chip, offset, val);
+	priv->data->set(chip, offset, val);
 
 	return 0;
 }
@@ -159,7 +163,7 @@ static int syscon_gpio_probe(struct platform_device *pdev)
 	if (priv->data->flags & GPIO_SYSCON_FEAT_IN)
 		priv->chip.direction_input = syscon_gpio_dir_in;
 	if (priv->data->flags & GPIO_SYSCON_FEAT_OUT) {
-		priv->chip.set = syscon_gpio_set;
+		priv->chip.set = priv->data->set ? : syscon_gpio_set;
 		priv->chip.direction_output = syscon_gpio_dir_out;
 	}