gpiolib: introduce gpio_chip setters that return values

Add new variants of the set() and set_multiple() callbacks that have
integer return values allowing to indicate failures to users of the GPIO
consumer API. Until we convert all GPIO providers treewide to using
them, they will live in parallel to the existing ones.

Make sure that providers cannot define both. Prefer the new ones and
only use the old ones as fallback.

Reviewed-by: Linus Walleij <[e-mail]>
Acked-by: Uwe Kleine-König <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Bartosz Golaszewski <[e-mail]>

drivers/gpio/gpiolib.c

···
 	int base = 0;
 	int ret = 0;
 
+	/* Only allow one set() and one set_multiple(). */
+	if ((gc->set && gc->set_rv) ||
+	    (gc->set_multiple && gc->set_multiple_rv))
+		return -EINVAL;
+
 	/*
 	 * First: allocate and populate the internal stat container, and
 	 * set up the struct device.
···
 
 static int gpiochip_set(struct gpio_chip *gc, unsigned int offset, int value)
 {
+	int ret;
+
 	lockdep_assert_held(&gc->gpiodev->srcu);
 
-	if (WARN_ON(unlikely(!gc->set)))
+	if (WARN_ON(unlikely(!gc->set && !gc->set_rv)))
 		return -EOPNOTSUPP;
+
+	if (gc->set_rv) {
+		ret = gc->set_rv(gc, offset, value);
+		if (ret > 0)
+			ret = -EBADE;
+
+		return ret;
+	}
 
 	gc->set(gc, offset, value);
 	return 0;
···
 
 	lockdep_assert_held(&gc->gpiodev->srcu);
 
-	if (WARN_ON(unlikely(!gc->set_multiple && !gc->set)))
+	if (WARN_ON(unlikely(!gc->set_multiple && !gc->set_multiple_rv)))
 		return -EOPNOTSUPP;
+
+	if (gc->set_multiple_rv) {
+		ret = gc->set_multiple_rv(gc, mask, bits);
+		if (ret > 0)
+			ret = -EBADE;
+
+		return ret;
+	}
 
 	if (gc->set_multiple) {
 		gc->set_multiple(gc, mask, bits);

include/linux/gpio/driver.h

···
  *	stores them in "bits", returns 0 on success or negative error
  * @set: assigns output value for signal "offset"
  * @set_multiple: assigns output values for multiple signals defined by "mask"
+ * @set_rv: assigns output value for signal "offset", returns 0 on success or
+ *          negative error value
+ * @set_multiple_rv: assigns output values for multiple signals defined by
+ *                   "mask", returns 0 on success or negative error value
  * @set_config: optional hook for all kinds of settings. Uses the same
  *	packed config format as generic pinconf. Must return 0 on success and
  *	a negative error number on failure.
···
 	void			(*set_multiple)(struct gpio_chip *gc,
 						unsigned long *mask,
 						unsigned long *bits);
+	int			(*set_rv)(struct gpio_chip *gc,
+					  unsigned int offset,
+					  int value);
+	int			(*set_multiple_rv)(struct gpio_chip *gc,
+						   unsigned long *mask,
+						   unsigned long *bits);
 	int			(*set_config)(struct gpio_chip *gc,
 					      unsigned int offset,
 					      unsigned long config);