gpio: generic: support input-only chips

Allow chips to indicates that they are input-only and thus cannot set
the output value. This will be used by the gpio-etraxfs driver.

Signed-off-by: Rabin Vincent <[e-mail]>
Signed-off-by: Linus Walleij <[e-mail]>

drivers/gpio/gpio-generic.c

···
 	return !!(bgc->read_reg(bgc->reg_dat) & bgc->pin2mask(bgc, gpio));
 }
 
+static void bgpio_set_none(struct gpio_chip *gc, unsigned int gpio, int val)
+{
+}
+
 static void bgpio_set(struct gpio_chip *gc, unsigned int gpio, int val)
 {
 	struct bgpio_chip *bgc = to_bgpio_chip(gc);
···
 static int bgpio_simple_dir_in(struct gpio_chip *gc, unsigned int gpio)
 {
 	return 0;
+}
+
+static int bgpio_dir_out_err(struct gpio_chip *gc, unsigned int gpio,
+				int val)
+{
+	return -EINVAL;
 }
 
 static int bgpio_simple_dir_out(struct gpio_chip *gc, unsigned int gpio,
···
 		bgc->reg_set = set;
 		bgc->gc.set = bgpio_set_set;
 		bgc->gc.set_multiple = bgpio_set_multiple_set;
+	} else if (flags & BGPIOF_NO_OUTPUT) {
+		bgc->gc.set = bgpio_set_none;
+		bgc->gc.set_multiple = NULL;
 	} else {
 		bgc->gc.set = bgpio_set;
 		bgc->gc.set_multiple = bgpio_set_multiple;
···
 
 static int bgpio_setup_direction(struct bgpio_chip *bgc,
 				 void __iomem *dirout,
-				 void __iomem *dirin)
+				 void __iomem *dirin,
+				 unsigned long flags)
 {
 	if (dirout && dirin) {
 		return -EINVAL;
···
 		bgc->gc.direction_input = bgpio_dir_in_inv;
 		bgc->gc.get_direction = bgpio_get_dir_inv;
 	} else {
-		bgc->gc.direction_output = bgpio_simple_dir_out;
+		if (flags & BGPIOF_NO_OUTPUT)
+			bgc->gc.direction_output = bgpio_dir_out_err;
+		else
+			bgc->gc.direction_output = bgpio_simple_dir_out;
 		bgc->gc.direction_input = bgpio_simple_dir_in;
 	}
 
···
 	if (ret)
 		return ret;
 
-	ret = bgpio_setup_direction(bgc, dirout, dirin);
+	ret = bgpio_setup_direction(bgc, dirout, dirin, flags);
 	if (ret)
 		return ret;
 

include/linux/basic_mmio_gpio.h

···
 #define BGPIOF_UNREADABLE_REG_DIR	BIT(2) /* reg_dir is unreadable */
 #define BGPIOF_BIG_ENDIAN_BYTE_ORDER	BIT(3)
 #define BGPIOF_READ_OUTPUT_REG_SET     BIT(4) /* reg_set stores output value */
+#define BGPIOF_NO_OUTPUT		BIT(5) /* only input */
 
 #endif /* __BASIC_MMIO_GPIO_H */