[PATCH v4 4/8] reset: Add reset_control_get_from_provider_exclusive()

[Geert Uytterhoeven]

When stacking two reset controllers, the upper one should go through the
proper channels: request exclusive reset controls and use them via the
reset_control_*() APIs.  However, unlike the clock subsystem, which has
of_clk_get_from_provider(), the reset subsystem does not offer a way to
lookup and obtain a reset from a reset provider.

Hence add a public helper reset_control_get_from_provider_exclusive()
to lookup and obtain an exclusive reference to a reset controller, based
on the recently introduced __reset_control_get_from_provider() helper.
This will be used by the R-Car X5H Module Controller driver.

Signed-off-by: Geert Uytterhoeven <geert+renesas at glider.be>
---
v4:
  - Check for overflow when converting (u64) fwnode args to (uint32_t)
    OF args,
  - Document that reset_control_get_from_provider_exclusive() must not
    be given a reference to a GPIO provider,
  - Let the dummy return ERR_PTR(-ENOTSUPP) instead of NULL,

v3:
  - Replace reset_controller_get_provider() by
    reset_control_get_from_provider_exclusive(),
  - Add kerneldoc,

v2:
  - No changes.
---
 drivers/reset/core.c  | 41 ++++++++++++++++++++++++++++++++++++-----
 include/linux/reset.h |  8 ++++++++
 2 files changed, 44 insertions(+), 5 deletions(-)

diff --git a/drivers/reset/core.c b/drivers/reset/core.c
index 0e11f4c81c10d601..421bcc4c89cc21ac 100644
--- a/drivers/reset/core.c
+++ b/drivers/reset/core.c
@@ -1141,6 +1141,7 @@ __reset_control_get_from_provider(const struct fwnode_reference_args *args,
 				  bool gpio_fallback,
 				  enum reset_control_flags flags)
 {
+	struct fwnode_handle *fwnode = consumer ?: args->fwnode;
 	struct reset_controller_dev *rcdev;
 	int rstc_id = -EINVAL;
 
@@ -1153,18 +1154,30 @@ __reset_control_get_from_provider(const struct fwnode_reference_args *args,
 	if (WARN_ON(args->nargs != rcdev->fwnode_reset_n_cells))
 		return ERR_PTR(-EINVAL);
 
-	if (rcdev->of_xlate && is_of_node(consumer)) {
-		struct device_node *np = to_of_node(consumer);
+	if (rcdev->of_xlate && is_of_node(fwnode)) {
+		struct device_node *np = to_of_node(fwnode);
 		struct of_phandle_args of_args;
 		int ret;
 
-		ret = of_parse_phandle_with_args(np,
+		if (consumer) {
+			ret = of_parse_phandle_with_args(np,
 					 gpio_fallback ? "reset-gpios" : "resets",
 					 gpio_fallback ? "#gpio-cells" : "#reset-cells",
 					 gpio_fallback ? 0 : index,
 					 &of_args);
-		if (ret)
-			return ERR_PTR(ret);
+			if (ret)
+				return ERR_PTR(ret);
+		} else {
+			of_args.np = of_node_get(np);
+			of_args.args_count = args->nargs;
+
+			for (unsigned int i = 0; i < args->nargs; i++) {
+				if (args->args[i] > U32_MAX)
+					return ERR_PTR(-EINVAL);
+
+				of_args.args[i] = args->args[i];
+			}
+		}
 
 		rstc_id = rcdev->of_xlate(rcdev, &of_args);
 		of_node_put(of_args.np);
@@ -1254,6 +1267,24 @@ struct reset_control *__reset_control_get(struct device *dev, const char *id,
 }
 EXPORT_SYMBOL_GPL(__reset_control_get);
 
+/**
+ * reset_control_get_from_provider_exclusive - Lookup and obtain an exclusive
+ *					       reference to a reset controller.
+ * @args: Reference to the reset controller provider with all the args like
+ *	  reset number.  This must not be a reference to a GPIO provider.
+ *
+ * Returns a struct reset_control or IS_ERR() condition containing errno.
+ * If this function is called more than once for the same reset control it will
+ * return -EBUSY.
+ */
+struct reset_control *
+reset_control_get_from_provider_exclusive(const struct fwnode_reference_args *args)
+{
+	return __reset_control_get_from_provider(args, NULL, 0, false,
+						 RESET_CONTROL_EXCLUSIVE);
+}
+EXPORT_SYMBOL_GPL(reset_control_get_from_provider_exclusive);
+
 int __reset_control_bulk_get(struct device *dev, int num_rstcs,
 			     struct reset_control_bulk_data *rstcs,
 			     enum reset_control_flags flags)
diff --git a/include/linux/reset.h b/include/linux/reset.h
index 9c391cf0c82298a0..384273ec0c7cbef7 100644
--- a/include/linux/reset.h
+++ b/include/linux/reset.h
@@ -90,6 +90,8 @@ struct reset_control *__fwnode_reset_control_get(struct fwnode_handle *fwnode,
 				     const char *id, int index, enum reset_control_flags flags);
 struct reset_control *__reset_control_get(struct device *dev, const char *id,
 					  int index, enum reset_control_flags flags);
+struct reset_control *reset_control_get_from_provider_exclusive(
+				const struct fwnode_reference_args *args);
 void reset_control_put(struct reset_control *rstc);
 int __reset_control_bulk_get(struct device *dev, int num_rstcs,
 			     struct reset_control_bulk_data *rstcs,
@@ -173,6 +175,12 @@ static inline struct reset_control *__reset_control_get(
 	return optional ? NULL : ERR_PTR(-ENOTSUPP);
 }
 
+static inline struct reset_control *reset_control_get_from_provider_exclusive(
+				const struct fwnode_reference_args *args)
+{
+	return ERR_PTR(-ENOTSUPP);
+}
+
 static inline int
 reset_control_bulk_reset(int num_rstcs, struct reset_control_bulk_data *rstcs)
 {
-- 
2.43.0