dm: gpio: add a default gpio xlate routine

Many drivers use a common form of offset + flags for device
tree nodes. e.g.:
	<&gpio1 2 GPIO_ACTIVE_LOW>

This patch adds a common implementation of this type of parsing
and calls it when a gpio driver doesn't supply its' own xlate
routine.

This will allow removal of the driver-specific versions in a
handful of drivers and simplify the addition of new drivers.

Signed-off-by: Eric Nelson <eric@nelint.com>
Reviewed-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Simon Glass <sjg@chromium.org>

drivers/gpio/gpio-uclass.c

@@ -6,6 +6,7 @@
 
 #include <common.h>
 #include <dm.h>
+#include <dt-bindings/gpio/gpio.h>
 #include <errno.h>
 #include <fdtdec.h>
 #include <malloc.h>
@@ -113,19 +114,33 @@ int gpio_lookup_name(const char *name, struct udevice **devp,
 	return 0;
 }
 
+int gpio_xlate_offs_flags(struct udevice *dev,
+					 struct gpio_desc *desc,
+					 struct fdtdec_phandle_args *args)
+{
+	if (args->args_count < 1)
+		return -EINVAL;
+
+	desc->offset = args->args[0];
+
+	if (args->args_count < 2)
+		return 0;
+
+	if (args->args[1] & GPIO_ACTIVE_LOW)
+		desc->flags = GPIOD_ACTIVE_LOW;
+
+	return 0;
+}
+
 static int gpio_find_and_xlate(struct gpio_desc *desc,
 			       struct fdtdec_phandle_args *args)
 {
 	struct dm_gpio_ops *ops = gpio_get_ops(desc->dev);
 
-	/* Use the first argument as the offset by default */
-	if (args->args_count > 0)
-		desc->offset = args->args[0];
+	if (ops->xlate)
+		return ops->xlate(desc->dev, desc, args);
 	else
-		desc->offset = -1;
-	desc->flags = 0;
-
-	return ops->xlate ? ops->xlate(desc->dev, desc, args) : 0;
+		return gpio_xlate_offs_flags(desc->dev, desc, args);
 }
 
 int dm_gpio_request(struct gpio_desc *desc, const char *label)
@@ -605,6 +620,7 @@ static int _gpio_request_by_name_nodev(const void *blob, int node,
 
 	desc->dev = NULL;
 	desc->offset = 0;
+	desc->flags = 0;
 	ret = fdtdec_parse_phandle_with_args(blob, node, list_name,
 					     "#gpio-cells", 0, index, &args);
 	if (ret) {

include/asm-generic/gpio.h

@@ -206,6 +206,16 @@ int gpio_requestf(unsigned gpio, const char *fmt, ...)
 
 struct fdtdec_phandle_args;
 
+/**
+ * gpio_xlate_offs_flags() - implementation for common use of dm_gpio_ops.xlate
+ *
+ * This routine sets the offset field to args[0] and the flags field to
+ * GPIOD_ACTIVE_LOW if the GPIO_ACTIVE_LOW flag is present in args[1].
+ *
+ */
+int gpio_xlate_offs_flags(struct udevice *dev, struct gpio_desc *desc,
+			  struct fdtdec_phandle_args *args);
+
 /**
  * struct struct dm_gpio_ops - Driver model GPIO operations
  *
@@ -258,12 +268,11 @@ struct dm_gpio_ops {
 	 *
 	 *   @desc->dev to @dev
 	 *   @desc->flags to 0
-	 *   @desc->offset to the value of the first argument in args, if any,
-	 *		otherwise -1 (which is invalid)
+	 *   @desc->offset to 0
 	 *
-	 * This method is optional so if the above defaults suit it can be
-	 * omitted. Typical behaviour is to set up the GPIOD_ACTIVE_LOW flag
-	 * in desc->flags.
+	 * This method is optional and defaults to gpio_xlate_offs_flags,
+	 * which will parse offset and the GPIO_ACTIVE_LOW flag in the first
+	 * two arguments.
 	 *
 	 * Note that @dev is passed in as a parameter to follow driver model
 	 * uclass conventions, even though it is already available as