drm/connector: Add a function to lookup a TV mode by its name

As part of the command line parsing rework coming in the next patches,
we'll need to lookup drm_connector_tv_mode values by their name, already
defined in drm_tv_mode_enum_list.

In order to avoid any code duplication, let's do a function that will
perform a lookup of a TV mode name and return its value.

Reviewed-by: Noralf Trønnes <noralf@tronnes.org>
Tested-by: Mateusz Kwiatkowski <kfyatek+publicgit@gmail.com>
Acked-in-principle-or-something-like-that-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://lore.kernel.org/r/20220728-rpi-analog-tv-properties-v10-7-256dad125326@cerno.tech
Signed-off-by: Maxime Ripard <maxime@cerno.tech>

drivers/gpu/drm/drm_connector.c

@@ -995,6 +995,30 @@ static const struct drm_prop_enum_list drm_tv_mode_enum_list[] = {
 };
 DRM_ENUM_NAME_FN(drm_get_tv_mode_name, drm_tv_mode_enum_list)
 
+/**
+ * drm_get_tv_mode_from_name - Translates a TV mode name into its enum value
+ * @name: TV Mode name we want to convert
+ * @len: Length of @name
+ *
+ * Translates @name into an enum drm_connector_tv_mode.
+ *
+ * Returns: the enum value on success, a negative errno otherwise.
+ */
+int drm_get_tv_mode_from_name(const char *name, size_t len)
+{
+	unsigned int i;
+
+	for (i = 0; i < ARRAY_SIZE(drm_tv_mode_enum_list); i++) {
+		const struct drm_prop_enum_list *item = &drm_tv_mode_enum_list[i];
+
+		if (strlen(item->name) == len && !strncmp(item->name, name, len))
+			return item->type;
+	}
+
+	return -EINVAL;
+}
+EXPORT_SYMBOL(drm_get_tv_mode_from_name);
+
 static const struct drm_prop_enum_list drm_tv_select_enum_list[] = {
 	{ DRM_MODE_SUBCONNECTOR_Automatic, "Automatic" }, /* DVI-I and TV-out */
 	{ DRM_MODE_SUBCONNECTOR_Composite, "Composite" }, /* TV-out */