[PATCH v5 05/10] gpiolib: Add gpio_property_name_length()

[Chen-Yu Tsai <wenst@chromium.org>]

The I2C device tree component prober needs to get and toggle GPIO lines
for the components it intends to probe. These components may not use the
same name for their GPIO lines, so the prober must go through the device
tree, check each property to see it is a GPIO property, and get the GPIO
line.

Instead of duplicating the GPIO suffixes, or exporting them to the
prober to do pattern matching, simply add and export a new function that
does the pattern matching and returns the length of the GPIO name. The
caller can then use that to copy out the name if it needs to.

Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>

---
Changes since v4:
- new patch

Depends on commit 4b91188dced8 ("gpiolib: Replace gpio_suffix_count
with NULL-terminated array").
---
 drivers/gpio/gpiolib.c        | 44 +++++++++++++++++++++++++++++++++++
 include/linux/gpio/consumer.h |  2 ++
 2 files changed, 46 insertions(+)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 3903d0a75304..e4228ef6f131 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -4295,6 +4295,50 @@ struct gpio_desc *fwnode_gpiod_get_index(struct fwnode_handle *fwnode,
 }
 EXPORT_SYMBOL_GPL(fwnode_gpiod_get_index);
 
+/**
+ * gpio_property_name_length - Returns the GPIO name length from a property name
+ * @str:	string to check
+ *
+ * This function checks if the given name matches the GPIO property patterns, and
+ * returns the length of the name of the GPIO. The pattern is "*-<GPIO suffix>"
+ * or just "<GPIO suffix>".
+ *
+ * Returns:
+ * The length of the string before '-' if it matches "*-<GPIO suffix>", or
+ * 0 if no name part, just the suffix, or
+ * -EINVAL if the string doesn't match the pattern.
+ */
+int gpio_property_name_length(const char *str)
+{
+	size_t len;
+
+	len = strlen(str);
+
+	/* string need to be at minimum len(gpio) */
+	if (len < 4)
+		return -EINVAL;
+
+	/* Check for no-name case: "gpio" / "gpios" */
+	for (const char *const *p = gpio_suffixes; *p; p++)
+		if (!strcmp(str, *p))
+			return 0;
+
+	for (size_t i = len - 4; i > 0; i--) {
+		/* find right-most '-' and check if remainder matches suffix */
+		if (str[i] != '-')
+			continue;
+
+		for (const char *const *p = gpio_suffixes; *p; p++)
+			if (!strcmp(str + i + 1, *p))
+				return i;
+
+		return -EINVAL;
+	}
+
+	return -EINVAL;
+}
+EXPORT_SYMBOL_GPL(gpio_property_name_length);
+
 /**
  * gpiod_count - return the number of GPIOs associated with a device / function
  *		or -ENOENT if no GPIO has been assigned to the requested function
diff --git a/include/linux/gpio/consumer.h b/include/linux/gpio/consumer.h
index db2dfbae8edb..ce3a5f86a037 100644
--- a/include/linux/gpio/consumer.h
+++ b/include/linux/gpio/consumer.h
@@ -56,6 +56,8 @@ enum gpiod_flags {
 
 #ifdef CONFIG_GPIOLIB
 
+int gpio_property_name_length(const char *name);
+
 /* Return the number of GPIOs associated with a device / function */
 int gpiod_count(struct device *dev, const char *con_id);
 
-- 
2.46.0.184.g6999bdac58-goog