pinctrl: add pinctrl_provide_dummies interface for platforms to use

Add a interface pinctrl_provide_dummies for platform to indicate
whether it needs use pinctrl dummy state.

ChangeLog v3->v4:
* remove dummy gpio support in pinctrl subsystem.
  Let gpio driver decide whether it wants to use pinctrl gpio mux
  function.
ChangeLog v2->v3:
* Also changed the missed pinctrl gpio APIs in v1.
ChangeLog v1->v2:
* Based on sascha's suggestion, drop using kconfig since it will hide
  pinctrl errors on all other boards.
  See: https://lkml.org/lkml/2012/4/18/282
  It seemed both Linus and Stephen agreed with this way, so i'm ok
  with it too.
* Add dummy gpio support.
  pinctrl gpio in the same situation as state.
* Patch name changed.
  Original is pinctrl: handle dummy state in core.
* Split removing old dt dummy interface into a separate patch

Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Stephen Warren <swarren@wwwdotorg.org>
Signed-off-by: Dong Aisheng <dong.aisheng@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/pinctrl/core.c

@@ -43,6 +43,8 @@ struct pinctrl_maps {
 	unsigned num_maps;
 };
 
+static bool pinctrl_dummy_state;
+
 /* Mutex taken by all entry points */
 DEFINE_MUTEX(pinctrl_mutex);
 
@@ -61,6 +63,19 @@ static LIST_HEAD(pinctrl_maps);
 			_i_ < _maps_node_->num_maps; \
 			i++, _map_ = &_maps_node_->maps[_i_])
 
+/**
+ * pinctrl_provide_dummies() - indicate if pinctrl provides dummy state support
+ *
+ * Usually this function is called by platforms without pinctrl driver support
+ * but run with some shared drivers using pinctrl APIs.
+ * After calling this function, the pinctrl core will return successfully
+ * with creating a dummy state for the driver to keep going smoothly.
+ */
+void pinctrl_provide_dummies(void)
+{
+	pinctrl_dummy_state = true;
+}
+
 const char *pinctrl_dev_get_name(struct pinctrl_dev *pctldev)
 {
 	/* We're not allowed to register devices without name */
@@ -719,8 +734,18 @@ static struct pinctrl_state *pinctrl_lookup_state_locked(struct pinctrl *p,
 	struct pinctrl_state *state;
 
 	state = find_state(p, name);
-	if (!state)
+	if (!state) {
+		if (pinctrl_dummy_state) {
+			/* create dummy state */
+			dev_dbg(p->dev, "using pinctrl dummy state (%s)\n",
+				name);
+			state = create_state(p, name);
+			if (IS_ERR(state))
+				return state;
+		} else {
 			return ERR_PTR(-ENODEV);
+		}
+	}
 
 	return state;
 }

include/linux/pinctrl/machine.h

@@ -154,7 +154,7 @@ struct pinctrl_map {
 
 extern int pinctrl_register_mappings(struct pinctrl_map const *map,
 				unsigned num_maps);
-
+extern void pinctrl_provide_dummies(void);
 #else
 
 static inline int pinctrl_register_mappings(struct pinctrl_map const *map,
@@ -163,5 +163,8 @@ static inline int pinctrl_register_mappings(struct pinctrl_map const *map,
 	return 0;
 }
 
+static inline void pinctrl_provide_dummies(void)
+{
+}
 #endif /* !CONFIG_PINCTRL */
 #endif